Annual report for 1998A new mechanism of leptogenesis is proposed in which the asymmetries in lepton numbers are produced through the CP-violating oscillations of "sterile" (electroweak singlet) neutrinos. The asymmetry is communicated from singlet neutrinos to ordinary leptons through their Yukawa couplings. The lepton asymmetry is then reprocessed into baryon asymmetry by electroweak sphalerons. The observed value of baryon asymmetry can be generated in this way, and the masses of ordinary neutrinos induced by the seesaw mechanism are in the astrophysically and cosmologically interesting range.
It is shown that "top-down" mechanisms of Ultra-High Energy Cosmic Rays which involve heavy relic particle-like objects predict Galactic anisotropy of highest energy cosmic rays at the level of minimum ~20%. This anisotropy is large enough to be either observed or ruled out in the next generation of experiments.
The consequences of messenger-matter mixing are studied in the context of the Minimal Gauge Mediated Model (MGMM). It is shown that existing experimental limits on mu -> e gamma decay, mu -> e conversion, K^0 - anti K^0, D^0 - anti D^0 and B^0 - anti B^0 mixings place significant constraints on relevant coupling constants and mixing parameters. On the other hand, the contributions of the messenger-matter mixing to the rates of tau -> e gamma, tau -> mu gamma and b -> s gamma are well below the present experimental limits. Radiative electroweak breaking in the MGMM with mixing is studied. It is found that in these models, unlike MGMM without mixing, a wide range of tan{beta} is allowed.
Sufficient conditions are established for the existence of stable non-topological solitons, Q-balls in electroweak models with low-energy supersymmetry breaking. These objects may have been created in the early Universe. It is found that the relic Q-balls can accumulate inside a neutron star and gradually absorb the baryons into the scalar condensate. This causes a slow reduction in the mass of the star. When the mass reaches a critical value, the neutron star becomes unstable and explodes. The cataclysmic destruction of the distant neutron stars may be the origin of the gamma-ray bursts.
We study deep-inelastic scattering of neutrino from nuclear targets in a wide kinematical range of x and Q^2. We develop a systematic expansion of nuclear structure functions in terms of Q^{-2} series caused by nuclear effects ("nuclear twist" series). Basing on this expansion we calculate nuclear corrections to a number of sum rules for the structure functions. In particular, we show that corrections to the Gross-Llewellyn-Smith sum rule due to nuclear effects cancel out in the Bjorken limit and calculate the corresponding Q^{-2} correction. Special attention is payed to the discussion of the off-shell effects in the structure functions. A sizable impact of these effects both on Q^2- and x-dependence of nuclear structure functions is found.
We discuss nuclear shadowing effect for the structure functions F_2 and F_3 in the small x region. It is shown that F_3 is shadowed about as twice as stronger as F_2 in nuclei. Phenomenological aspects of this effect are discussed.
The first three-loop QCD analysis of the data for xF_3 structure function of deep-inelastic neutrino-nucleon scattering, obtained by CCFR collaboration at Fermilab Tevatron, is performed. The values of alpha_s(M_Z) and twist-four power corrections are extracted. The theoretical ambiguities of this analysis are estimated using [0/2] Pade approximants.
The total cross section of the top quark-antiquark pair production near threshold in gamma gamma collision is computed analytically up to the next-to-leading order in perturbative and nonrelativistic expansion for general photon helicity. The approximation includes the first order corrections in the strong coupling constant and the heavy quark velocity to the nonrelativistic Coulomb approximation. A correlator of the vector current of a heavy quark is computed analytically near threshold in the next-to-next-to-leading order in perturbative and relativistic expansion that includes al_s^2, al_sv and v^2 corrections in the coupling constant and velocity of the heavy quark to the nonrelativistic Coulomb approximation. Based on this result, the numerical values of the b-quark pole mass and the strong coupling constant are determined from the analysis of sum rules for the Upsilon system. The next-to-next-to-leading corrections are found to be of order of next-to-leading ones.
New local symmetries for the Regge limit of gluodynamics are found. The Regge limit allows one to study high-energy collisions of elementary particles. The emergence of the extra symmetries is a consequence of simplifications of the theory justified in the Regge limit.
Manifestations of the BFKL-pomeron are found in the data on inclusive production of hadronic jets in proton-antiproton collisions. In particular, the dependence of the R-ratio of inclusive single-jet cross sections measured at different values of the collision energy on the fraction of the collision energy deposited in the tagged jet is in accord with the BFKL calculations and contradicts finite order perturbative calculations.
A consistent analysis of Upsilon sum rules and B-meson semileptonic width in the next-to-next-to-leading order in the strong coupling constant was performed. The analysis is based on the analytical result for the heavy quark vector current correlator near threshold in the second order in perturbative and relativistic expansion around the nonrelativistic Coulomb approximation. The total cross section of the top quark-antiquark pair production near threshold in gammagamma collision is computed analytically up to the next-to-leading order in perturbative and nonrelativistic expansion for general photon helicity. The approximation includes the first order corrections in the strong coupling constant and the heavy quark velocity to the nonrelativistic Coulomb approximation.
An efficient configuration space technique which allows one to compute a class of Feynman diagrams which generalize the scalar sunset topology to any number of massive internal lines is introduced. General tensor vertex structures and modifications of the propagators due to particle emission with vanishing momenta can be included with only a little change of the basic technique described for the scalar case. Applications to the computation of n-body phase space in D-dimensional space-time are discussed. Substantial simplifications occur for odd space-time dimensions where the final results can be expressed in closed form through rational functions. Explicit analytical formulas for three-dimensional space-time are presented.
It is proposed to use the techniques of separation of contributions of the states with different spin-parity to the semileptonic tau decay rate, that then allows four independent quark mass determinations. Eventually even different moments of their respective spectral functions have been considered, leading to additional tests of the method. The rate for 0^+ might be the most promising candidate. This configuration is strictly forbidden in the limit of massless quarks - the corresponding rate is thus a direct measure for the strange quark mass in Cabbibo suppressed tau lepton decays. Quadratic quark mass corrections to the decay rate ratio R_{tau} to the order O(alpha_s^3 m^2) and find that they contribute appreciably to the Cabbibo suppressed decay modes of the tau-lepton are calculated. Theoretical analysis of the PT series is presented.
A toy model has been constructed where supersymmetry breaking and compositeness of the Standard model matter arise from one and the same dynamical mechanism. A new method was suggested to constrain the parameters of multi-messenger gauge mediated supersymmetry breaking models.
The highest energy cosmic rays, above the Greisen-Zatsepin-Kuzmin cut-off of cosmic ray spectrum, may be produced in decays of superheavy long-living X-particles. We conjecture that these particles may be produced naturally in the early Universe from vacuum fluctuations during inflation and may constitute a considerable fraction of Cold Dark Matter. We predict a new cut-off in the UHE cosmic ray spectrum E_{cut-off} < m_inflaton ~= 10^13 GeV, the exact position of the cut-off and the shape of the cosmic ray spectrum beyond the GZK cut-off being determined by the QCD quark/gluon fragmentation. The Pierre Auger Project installation might discover this phenomenon.
Cosmic rays of the highest energy, above the Greisen-Zatsepin-Kuzmin cut-off of the spectrum, may originate in decays of superheavy long-living X-particles. These particles may be produced in the early Universe from vacuum fluctuations during or after inflation and may constitute a considerable fraction of Cold Dark Matter. We calculate numerically their abundance for a wide range of models. X-particles are considered to be either bosons or fermions. Particles that are several times heavier than inflaton, m_inflaton ~= 10^13 GeV, and were produced by this mechanism, can account for the critical mass in the Universe naturally. In some cases induced isocurvature density fluctuations can leave an imprint in anisotropy of cosmic microwave background radiation.
The impact of unstable Majorana tau neutrinos on primordial nucleosynthesis is considered. The mass and lifetime of nu_tau are taken in the intervals 0.1 - 20 MeV and 0.001 - 400 sec respectively. The studied decay modes are nu_tau -> nu_mu + phi and nu_tau -> nu_e + phi, where phi is a massless (or light) scalar. Integro-differential kinetic equations are solved numerically without any simplifying assumptions. Our results deviate rather strongly from the earlier calculations. Depending on mass, lifetime, and decay channels of the nu_tau, the number of effective neutrino species (found from He4), in addition to the 3 standard ones, varies from -2 to +2.5. The abundances of H2 and Li7 are also calculated.
We repeated our previous calculation of the spectrum distortion of massless neutrinos in the early universe with a considerably better accuracy and corrected for a missing numerical factor in one of the two ways of calculations presented in hep-ph/9703315. Now both ways of calculations are in perfect agreement and we essentially reproduce our old results presented in the abstract of the paper and used in the calculations of light element abundances. We disagree with the criticism of our calculations presented in astro-ph/9712199.
The influence of a massive Majorana tau-neutrino on primordial nucleosynthesis is rigorously calculated. The system of three integro-differential kinetic equations is solved numerically for the tau-neutrino mass in the interval from 0 to 20 MeV. It is found that the usual assumption of kinetic equilibrium is strongly violated and non-equilibrium corrections considerably amplify the effect. Even a very weak restriction from nucleosynthesis, allowing for one extra massless neutrino species, permits to conclude that m_nu_tau < 1 MeV. For a stricter bound, e.g. for dN < 0.3, the limit is m_nu_tau < 0.35 MeV.
Theories with low-energy supersymmetry predict the existence of stable non-topological solitons, Q-balls, that can contribute to dark matter. We discuss the experimental signatures, methods of detection, and the present limits on such dark matter candidates.
Sphaleron transitions in the course of thermalization of highly non-equilibrium initial field configurations were numerically investigated in (1+1)-dimensional Abelian two-Higgs model. It was shown that the transition rate is sensitive to deviations from thermal equilibrium and the process of thermalization can be very slow.
The rate of nonequilibrium transitions is changing according to variations of effective temperature, calculated over low-momentum spectral modes of the Higgs field. Nonequilibrium sphaleron transitions were also studied in the framework of reheating processes in early Universe. Their applications to the problem of baryogenesis are currently being investigated.
It is shown that new light gauge boson which might be produced in the decays of pseudoscalar mesons could be effectively searched for in neutrino experiments via the Primakoff effect. An estimate of the branching ratio of new gauge boson in pi^0 decay for the NOMAD neutrino detector at CERN is given.
New iterpretation of the KARMEN anomaly is proposed. A new experiment for the verification of the KARMEN anomaly is suggested.
A new method for an estimation of the probability of new physics discovery in future experiments is proposed. A method for taking into account the systematical erroes related to nonexact knowledge of background and signal cross sections is proposed.
Gaugino pair production at LHC(CMS) with subsequent decays into leptons for the case of nonuniversal gaugino masses is investigated. Visibility of signal by an excess over SM background depends rather strongly on the relation between LSP mass and chargino mass.
Phenomenology of electroweak supersymmetric model with Dirac neutrino has been considered. It is found that for significant part of parameter space tau slepton is a longlived particle.
INR Accelerator Department Activity In 1998 is as follows:
1. Moscow Meson Factory Lulac provided 2000 beam hours in 1998. Maximum beam energy was limited by 210 MeV for economical reason. Most of the beam time has been devoted to isotope production for medical purpose.
2. Local automatic system based on IBM PC and MOON Lab computer software for beam diagnostics has been put into operation. The system provides the data acquisition from beam transformers, wire scanners, harps and beam loss monitors.
3. A great bulk of works intended to injection system upgrade has been worked out. RFQ booster and RFQ - DTL matching section have been manufactured, tested and put into operation. The aim of that upgrade is to increase twice the beam average current in production shifts.
4. Automatic control system of the beam size and position on isotope production target has been developed and implemented. The system increases the hardware radiation protection.
5. Study of polarized hydrogen atoms storage in the resonant charge-exchange ionizer of the INR. polarized ion source allowed us to increase the peak current up to 11 mA, polarization of 0.8 within normalized emittance of 1.0 pi*mm*mrad, pulse length of 200 mcs at the repetition rate of 5 Hz. Record peak current and figure of merit I*P^2 ~ 7 mA has been obtained.
6. In a course of international collaboration a number of special hardware has been developed and manufactured, including:
7. A great deal of new equipment (delay line chopper, BLVD monitor etc.) and important improvements in MMF Linac systems have been implemented.
1. A neutron source has been put into operation. By means of the source neutron spectra have been registered and measured.
2. In the run of December , 1998 a beam was transported to the neutron source target. We tried hard to find a way to make it as narrow as possible. And as a result we managed to get a beam with sigma equal to 1.7 mm.
3. A computr-aided system for diagnostics of the beam of the channel for transporting the protons to the neutron source has been made. A remote input/output system for profile monitors came to life.
4. In collaboration with the kaon physics department we developed, manufactured and mounted the automated system for beam current measurement with a sensitivity better than 0.1 mA in a pulse.
5. A vacuum system of the channel up to the neutron source has been modernized in a such way as to make it possible to transport the beam to the source. We completed the system for vacuum remote control which is also used for controlling vacuum seals on sections 1-7 of the vacuum system.
6. Equipment of the neutron source which includes a gas tank, a remotely jointed seal, a set of plugs of biological protection, an ampoule and its protection has been mounted.
7. Neutron source equipment has been technologically prepared.
8. A system for receiving and keeping drainage water of the first cooling loop of the neutron source is also ready to operate.
9. Auxiliary facilities and a sampling line of the automated system have been mounted.
10. Transparent profile monitors have been manufactured to be placed in front of the neutron source.
The further development of the universal code SHIELD, as a tool for hadron cascade transport modeling in targets with complex composition and shape, was done. In comparison with other codes (HETC, FLUKA, GEANT), SHIELD has an advantage in modeling of hadron transport in matter with energies up to 1 TeV. The code includes now a description of heavy ions (atoms with arbitrary weights) passing through materials. The code SHIELD will appear in the Radiation Safety Information Computational Center' s library (ORNL, U.S.A.).
Experimental data on radionuclide production cross-section in nuclear reactions at intermediate energies were collected and compiled for the Landolt-Boernstein handbook series that is published by the Springer-Verlag Publishing House (Germany).
On a base of the homogeneous nucleation theory, an analytical consideration of copper atoms clustering kinetics in supersaturated substituting solid solutions of alloys Fe-xCu (x = 0.1 - 1.5 at. %) was carried out for the first time. Results on the number density and average dimensions of clusters and the time-scale of the process are in a good agreement with experimental data on annealing, as well as describe microstructure evolution under electron irradiation. The realised consideration shows a necessity of taking into account the influence of cascades in atom-atomic collisions to the clustering kinetics under neutron irradiation. Such an improvement of the theory becomes a key-issue for any comprehensive analysis of property degradation in nuclear reactor pressure vessels.
Numerical calculations for transient kinetics of interstitial loop nucleation and growth at conditions of enhanced di-interstitial formation (temperatures below one third part of the melting point and/or high defect production rate) were realized. The results confirm the previous analytical consideration. Calculations are based on a new model of dimer formation reaction for high intensity of monomer generation. The enhanced formation of migrating di-interstitials may reduce the number of freely migrating interstitials and changes density and dimensions of interstitial dislocation loops.
Cross-sections for (n, gamma) reactions in Cu and Mn with natural compositions were measured at the Superluminous Lead Slowing-Down Neutron Spectrometer (LNS). Data on spectrometer resolution and gamma background show that the LNS, which is operating at the proton beam, has no additional sources of background gamma irradiation being compared with similar installations. A proposal of big 100-tons LNS with expected intensity of neutrons 10^15-10^16 n/s is prepared.
At the beam stop of protons (the irradiation facility RADEX-15), some current work on beam diagnostics and further preparations for irradiation experiments was done.
Problem of search for electronic antineutrino mass
V.M.Lobashev, O.V.Kazachenko
The end point region of the tritium beta-spectrum has been further studied on the "Troitsk nu-mass" set-up during 1998. Fits to the data give a corroboration for the existence of a step-like structure placed 5-15 eV below the end point with a relative intensity about 10^{-10}. The most interesting feature of this step is a periodical shift of its position with respect to the end point. The measurements which were carried out at the end of 1997 and in 1998 together with the previous data give a period of the shift variation 0.504 +- 0.003 year. The coincidence of this value with a half of the period of Earth rotation around the Sun allows one to discuss on a new basis the possibility of the explanation of the observed effect by the capture of low energy degenerate relic neutrinos which are concentrated around the Sun in a cloud with a density of about 0.5*10^15 nu/cm^3. In spite of the very speculative nature of this hypothesis it stimulates new measurements and development of new spectrometers with higher sensitivity.
An upper limit for the neutrino mass including data of 1994-1998 runs is: m_nu < 2.5 eV/c^2 at 95% C.L.
Measurement of the Flavor-Conserving Hadronic Week Interaction.
(TRIUMF Experiment E497)
V.M.Lobashev, N.A.Titov
Experiment E497 aims to measure the parity violating longitudinal analyzing power Az in proton - proton scattering at 221 MeV.
Two 5-week data taking runs were realized during December 1997 - January 1998 and July - August 1998. Preliminary analysis result for the first one is dominated by systematic uncertainties:
Az=(0.8 +/- 1.8(sys.))*10^{-7}
Data taking during the second run was performed in the mode that supposed to produce much less systematic errors.
A data analysis of February 1997 data run was completed. With improved understanding of systematic corrections it gives:
Az=(.33 +/- .57(stat.) +/- .31(sys.))*10^{-7}
Analysis and reduction of two dominant false effects connected with residual transversal polarization distribution of extracted beam and beam energy modulation at polarized ion source were done.
Search for T-odd muon polarization in decay of positive kaon to muon
Yu.G.Kudenko
The main goal of the E246 experiment (collaboration INR RAS-KEK) is a search for T-odd muon polarization in decay of positive kaon to muon, neutral pion and neutrino (Kmu3 - decay). Standard Model predicts no effect.
Thus, a discovery of non-zero T-odd polarization would be an indication of new physics beyond the SM. This experiment is a pure test of non-standard models and would help in the understanding of the observed CP-violation. The experiment is carrying out at 12 GeV proton synchrotron at KEK, Japan. The final sesitivity to the T-violating muon polarization is expected at a level of 0.0009. At the present moment first stage of the experiment is completed. Available experimental data provide the sesitivity to the T-violating muon polarization of 0.003. First results of the measurement are obtained and published.
Search for rare decay K_L --> pi0 nu anti nu Experiment E926
Yu.G.Kudenko
E926 is a proposed experiment to search for the rare decay K_L to pi0 nu anti nu. It received scientific approval from AGS PAC in October 1996 and is now in an R&D phase. K_L to pi0 nu anti nu is generally considered the most worthwhile quarry in the K system, and one of the most desirable in all of particle physics, because of its potential for elucidating CP-violation. The measurement is a very difficult one, since the expected branching ratio is ~2*10^{-11}, and the signature is poor. It requires a large high-performance detector. In particular it is necessary to completely reconstruct the kinematics of kaon decay to suppress backgrounds and obtain K_L to pi0 nu anti nu event. The goal of the experiment is to measure the CP-vioalting complex phase parameter eta with the precision of about 15%. The standard Model origin of CP-violation will be confirmed or the absence of this decay can be established at a level no consistent with the Standard Model.
Baryonic systems and problems of fermions
V.B.Kopeliovich, S.V.Zenkin
During 1998 the chiral soliton models were applied for studies of the possibilities of the existence of baryonic states with charm and bottom stable relative to the strong interactions. It was shown that baryonic systems with charm and bottom have more chances to be bound in comparison with those with strangeness.
In 1999 it is supposed to continue the search for classical chiral fields configurations of minimal energy in the models with SU(N) symmetry, and applications of these models for calculations of the spectra of observable states.
Experiment to search mu --> e conversion process (MECO, MELC)
V.M.Lobashev, R.M.Djilkibaev
Next simulations:
1) a proton target of the muon source
2) a shield of the superconducting solenoid
3) a magnetic field optimization of the muon source
have been done:
Results:
1) Two high melting temperature materials - carbon and tungsten for the proton target have been considered. They allow us to use the simple technique of radiative cooling as indicated the target radiation heating simulation the target durability is 10^7 sec for average proton current 200 mcA. By this means the target durability compares favourably with the run time of the experiment.
2) For calculation of solenoid coil radiation heating three different hadron codes GHEISHA, FLUKA and SHIELD have been used. The radiation heating simulations evidence that the total coil heating through neutron and gamma interactions will not exceed 25 Watt behind the coil Cu shield with 50 cm thickness. A such level of the radiation heating is 10% of the total coil heating at the cost of warm conductivity.
3) The muon source magnetic system consists of meson production part and S - form transport solenoid. The transport solenoid is required to produce positive or negative muon beam, to suppress neutral beam particles and to increase the beam monochromaticity.
A code for magnetic field calculation taking into account real geometry of the transport solenoid coils has been developed using the Biot and Savart law. The muon beam simulations were performed for two proton target with a diameter of 2 cm from carbon with length 16 cm and from tungsten with length 1.4 cm. Using the carbon target tend to increase muon beam intensity in a few times. The beam intensity for positive and for negative muons increased by a factor of 6.8 and 1.9 for the carbon target respectively.
Investigation of the subthreshold pion production in atomic nuclei on the proton beam channel at the Moscow Meson Facility
A.Reshetin
By using the PLASMAS set-up - the telescopic scintillation and semiconductor counter spectrometer, a new experimental evidence for the pion production on nuclei in the subthreshold energy range of protons has been obtained. The data processing and theoretical interpretation of the experiments, performed in 1996-1997 provide the physical information about collective effects in high-excitation nuclear states. In the framework of this project in 1996-1997 the five experimental runs with a total duration of 636 hr (53 shifts) with the linear proton accelerator at the Moscow Meson Facility (MMF) have been carried out. The real data acquisition time during the experimental runs was about 180 hours.
During the experimental test run with the PLASMAS set-up in 1998 a fast time-of-flight scintillation counter system was examined. Besides the test measurements showed that the accidental coincidence background for the spectrometer of pair-correlated particles (pi-d), (pi-t), (pi-He(3)), (pi-He(4)) for the mean proton beam current of about 1 mcA and for the macrostructure frequency of about 50 Hz is 0.1-0.2 accidental events for 1 s and is not essential for extraction of pair events in the further experiments.
During four experimental physical runs proton energy dependencies of the pion production cross section and of the pion yield ratio N(pi+)/N(pi-) for reactions Cu(p,pi+)X, Cu(p,pi-)X, 12C(p,pi+)X and 12C(p,pi-)X for 10 incident proton energies: 159, 175, 180, 185, 192, 193,5 209, 211, 250, 305 MeV, for 105 degree production angle and for a beam current of 1-2 nA were measured for the first time in the world practice. The overall experimental energy range of pions was found to be 14-48 MeV. The good agreement of the obtained results at incident proton energies of 175, 192 and 193,5 MeV for the cooper nucleus during the two 1996 and 1997 experimental runs at MMF proves a high experimental reproducibility and low systematic inaccuracy of the data for the PLASMAS set-up. New data at incident proton energy of 180 MeV on the cooper nucleus show some irregularity (about 4-5 sigma) in the smooth proton energy dependence of the pion yield ratio N(pi+)/N(pi-) (pion yield was integrated in the energy range of pions 14-48 MeV), measured with a proton energy step of about 5 MeV. No such irregularity was observed in the analogous proton energy dependence for the pion energy range of 14-22 MeV (the lowest range for experimental pion energies), however, this irregularity has a sharp form for the pion energy range of 22-30 MeV at poor data statistics.
At the same time experimental data show that there are not any significant irregularities in the smooth proton energy dependences of the pion yield ratio N(pi+)/N(pi-) for the carbon nucleus. It can be supposed that the anomaly in the proton energy dependence of the ratio N(pi+)/N(pi-) for the cooper nucleus observed in the PLASMAS set-up experiments (1996-1997) at an incident proton energy of 180 MeV is interpreted by the formation of the delta-resonance high-excitation cooper nuclear state followed by the single-pion emission. However, this 180 MeV high-excitation state is absent for the carbon nucleus. To describe the subthreshold and near threshold meson production in pA-interactions a new model was developed in the framework of the project in 1998. It is based on direct and two-step mechanisms and takes into account the nuclear spectral function obtained from the electron quasi-elastic scattering experiments on nuclei and from the many-body calculations with realistic NN-interaction models. The model was applied to the description of the subthreshold and near threshold kaon and near threshold charged pion production on nuclei in proton-induced reactions. Its applicability to the analysis of the subthreshold and near threshold pion and kaon production phenomenon has been demonstrated.
Study of rare pion-nuclear reactions with AMPIR installation
A.B.Kurepin
The work wasn't performed in 1998 because of the absence of the financial support.
Study of pion-nucleus and nucleus-nucleus reactions with KASPIY installation
A.B.Kurepin
Data treatment of the measurements is continued and physical analysis of the results of the experiment on study of pion, kaon and antiproton production by protons, deuterons and carbon nuclei collisions with nuclei is done. Most part of the data was received using the KASPIY installation at LHE JINR. Experimental results of some other laboratories were also used in physical analysis.
The developed methods of the analysis allow one to plan the analogous measurements on the same subject at higher energies. The estimations of the cross sections of super heavy particles yield on colliders as well as strangelets and cosmic objects of CENTAURO type have been done. The analysis of the precursor phenomena in heavy ion collisions is also done.
a). "Study of pion production on proton channel of the MMF accelerator" (mutual Russian-Italian experiment).
b). "Study of the collective effects and non nucleon degrees of freedom in nuclei in pion production from proton-nucleus and heavy ions collisions".
A.B.Kurepin
An analysis of the data from the experiment on pion production by protons on copper nuclei has been done. A narrow resonance structure existence in the Copper nuclei excitation function at proton energies 348-350 MeV was cofirmed. It was shown that anomalous behavior of the pion energy spectra at these energies could be explained by enhanced yield of low energy pions.
"Study of nucleus-nucleus collisions at ALICE installation on LHC accelerator collider beams (CERN)"
A.B.Kurepin
The main goal of the experiment is the search for collective effects and signals of ordinary hadronic matter phase transition to Quark-Gluon Plasma formation in nucleus-nucleus collisions under extremely high energies.
The INR group takes part in production of the particle identification detector at high momentum using ring Cherenkov counters. First prototypes of the quartz windows of large square with high transparency to ultraviolet radiation have been developed and produced. The installation for covering and testing of CsI sensitive slides for the RICH detector was created.
The calculations and optimization of dimuon spectrometer absorber were done.
The work on new subprojects: CASTOR - search for events of CENTAURO type and START - for trigger system is in progress now.
Study of muon pairs and vector mesons production in relativistic nucleus-nucleus collisions (NA50 experiment, CERN).
A.B.Kurepin
Only one Institute from Russia - INR RAS participates in the experiment.
The purpose of the experiment is the search for the effects to be observed if Quark-Gluon Plasma is formed during collision: suppression of the charmonia production, changes in omega, ro and phi mesons production.
Data taking: three lead ion beam runs and some proton beam runs.
The most important result is the observation of the anomalous suppression of the J/psi production in Pb-Pb collisions which could be explained as an evidence of QGP formation.
The contribution of the INR group is the construction and production of the unique BeO preabsorber, two systems of anticoincidence antihalo detectors to eliminate dimuon background from lead fragmentation events. INR group performs data analysis of the J/psi transverse momentum distribution as a function of centrality. Upgrade of the installation based on the pixel vertex detectors and additional magnet near target station for better momentum and mass resolution is planned.
"Dilepton spectrometer HADES" - in collaboration with Institute for High Ion Physics, Darmstadt, Germany
F.F.Guber, A.B.Kurepin
The agreement about scientific cooperation inside the International collaboration HADES between Institute for Nuclear Research RAS (INR, RAS) and GSI (Darmstadt, Germany) was signed in 1998. The properties of ro, omega and phi mesons inside the nuclei a planned to be studied in hadron and heavy ion collisions at energies up to 2 GeV/nucleon by measurement of two electrons from meson's decay in nuclear medium with wideapperture dielectron spectrometer HADES.
Contribution of INR is:
the mechanical constructions for installation and alignment of scintillation hodoscopes, drift chambers and shower detectors for HADES were produced in the mechanical department of INR;
two prototypes of lead convertor of electrons for shower detector were produced and tested;
the prototype of Cherenkov hodoscope for time-of-flight system of HADES installation intended for working in intensive relativistic nuclei beams was developed and produced. It was tested at GSI 1 GeV/nucleon uranium beam. The time resolution less than 100 psec was obtained;
the prototype of wide square scintillation detector for time-of-flight start hodoscope of HADES installation was produced at INR and tested at GSI.
PHENIX installation (in collaboration with Brookhaven National Laboratory, USA).
A.B.Kurepin
It was suggested by INR to upgrade the muon spectrometer preabsorber construction in order to improve the effective mass resolution of two muons from phi, J/psi and Y vector mesons decay
In the base of muon spectrometer installation the copper preabsorber is used. In this case the effective mass resolution is 110 MeV for phi mesons, 135 MeV for J/psi mesons and 200 MeV for Y mesons. The main contribution to the resolution is determined by muon multiple scattering in preabsorber material. To decrease this contribution the BeO as preabsorber was proposed with reasonable improvement of dimuon effective mass resolution: 76 MeV for phi mesons, 98 MeV for J/psi mesons and 177 MeV for Y mesons. Besides phi meson acceptance increases more than twice but the occupancy of the first three trek detectors grows on 20-30% in this case. The calculations are in progress now to optimize the dimuon effective mass resolution, occupancy of the trek detectors and the cost of new oxide aluminium or carbide bore preabsorbers.
Study of the pion double charge exchange reaction on liquid 3He target with CHAOS spectrometer (Experiment E-735 in collaboration with TRIUMF, Canada).
A.B.Kurepin
The purpose of the experiment is the search for narrow dibaryon state d' with the mass 2.065 GeV in pion double charge exchanged reaction on few nucleon system. INR group took part in data taking and data analysis. The article on measurement of the high level of three neutron production in pion charge exchange reaction on 3He was prepared for publication in 1998.
Experiment to detect double-lambda hypernuclei by observing characteristic pi mesonic decays (in collaboration with Brookhaven National Laboratory, USA).
A.B.Kurepin
The experiment was proposed by the collaboration of 11 Institutes from Japan, USA and Canada with participation of INR, Moscow. It was planned to use a new method for production and observation of double Lambda-hypernuclei by a measurement of consequent pion decay of hypernuclei with a resolution of about 1.7 MeV in the reaction (K-, K+) on nuclei with intensities by two order of magnitude higher than in the previous experiments The experiment was approved by PAC of BNL in November 1994. For the physical measurements in 1998 about 1200 hours of K- -beam time on AGS are to be attributed.
According to the scientific program and the Memorandum of Understanding the INR group, Moscow, is responsible for construction, tuning and running during the preparation and working on the beam of the Cylindrical Detector System (CDS), which is formed by cylindrical wire drift chamber with a diameter of 0.8 m and a length of 1 m for detection of polar coordinates of secondary particles and by two sector wire proportional chambers, placed outside of the cylindrical drift chamber to detect the z-coordinates of charged particles. The participants from INR took part in construction and tuning of the installation in KEK, Tsukuba, Japan, and in the recent test of the installation in BNL, USA, during 1996-1997.
The successful test of the detector system will be followed by the first physical run in Autumn 1998, and two scientists from INR will participate. The second physical run and the analysis of the obtained results are planned in 1999.
The development of transfer neutron theory in the different systems and application to solution of nuclear physics and astrophysics problem
M.V.Kazarnovsky
The setup for generation of intensive neutron fluxes with close to Maxwellian energy distribution at temperatures of T=10-20 KeV (quasistellar neutrons, or QSN) was created in LNF JINR. Tuning and setup properties measurements are currently under way.
An original setup for intensive QSN fluxes generation on the surface of small blocks of light moderator irradiated by neutrons from the Li-7(p,n) reaction near threshold was proposed and designed.
This kind of setup has important advantages over the setup for T=20-40 KeV QSN generation based on the lead moderator and previously planned to be constructed. So it was decided to create a new version of the setup in INR RAS.
Such a setup was constructed on the base of electrostatic generator EG-2.5 of Atomic Nuclei Laboratory, and its properties are now under investigation.
The experiment for WIMP search
B.M.Ovchinnikov
The neutrino research group of experimental physics department INR in collaboration with Baksan Neutrino Observatory are preparing the experiment for Weak Interactions Massive Particles search with two-phase Xe ionization chamber. The expected background in the experiment is equal to ten in power minus five of events/(kg*day).
The method for low energy neutrino detection
The neutrino research group of experimental physics department INR is developing the method for sun proton cycle neutrino (E_nu <= 0.42 MeV) detection by nu-scattering in das TPC. The useful effect can be extracted from the background by determining of angle direction for neutrino flow. The method was experimentally tested with 40-67 keV electrons (63 Ni).
Development of the Cascade-Evaporation-Fission model of intermediate energy particles interaction with nuclei.
A.S.Ilyinov, Yu.V.Ryabov
1.Production of strange particles and hypernuclei in proton-nucleus and pion-nucleus interactions.
The production of Lambda-hyperons in pi+A-interaction is investigated in the framework of the INC model. The properties of produced ensemble of hypernuclei were studied (distribution on excitation energy, momentum, angular momentum, charge and mass of residuals). It was shown that initial momentum of pi+ around 1 GeV/c is optimal for production of heavy hypernuclei. The fission cross section for heavy hypernuclei was calculated. It was proposed to measure the fission barriers and level density of hypernuclei in the reaction (pi+,K+f).
2. Studies of the channel of nuclear fission by protons accompanied by pion emission
Properties of the channel of nuclear fission by protons accompanied by pion emission have been predicted in the framework of cascade-evaporation-fission model. These properties are the energy dependence of total cross section of the channel in the primary energy interval from 150 MeV to 600 MeV, the angular and energy spectra of pions, the properties of excited residual nuclei, and mass-energy distribution of fission fragments. The results are applied for construction of experimental set-up to observe this channel at Moscow meson facility.
3. Studies of hot nuclei formation in nuclear reactions induced by intermediate-energy particles.
New data on formation of hot nuclei in nuclear reactions induced by intermediate-energy particles(p,p-,3He,4He) obtained in 4pi-experiments with registration of all secondaries (neutrons, charged particles, fission fragments) have been analyzed. It was shown that residual nuclei, which excitation energy is close to the limiting value about 1 GeV, are formed with some probability in the reactions. The shape of hot nuclei was determined, and its dependence on impact parameter, primary energy and projectile type was studied.
4. Studies of mechanisms of formation and decay of hot nuclei in electromagnetic excitation of ultrarelativistic heavy ions.
The nuclear spallation by strong electromagnetic fields induced by ultrarelativistic heavy ions has been investigated. The multistage model of this process has been developed. It takes into account: (1) the absorption of virtual photon by nucleus, (2) the intranuclear cascade of hadrons produced, (3) the statistical decay of excited residual nucleus. It was predicted that electromagnetic multifragmentation is an important mechanism at RHIC and LHC energies. The results were published in paper: I.A.Pshenichnov et al. Phys. Rev. 57C(1998)1920.
The laboratory continued research activities in three areas:
1. Studying the fluxes of neutrino, gamma-rays, and nuclei of the primary cosmic radiation;
2. Studying the core structure of Extensive Air Showers;
3. Investigations of principles of design and technical feasibility of creating a muon detector for the SHAL-1000 array project.
1.1. Accumulation and processing of the experimental data under the program of detecting the flux of neutrino-induced muons from the lower hemisphere. Total live time of observations is about 13 years. The ratio of the number of experimentally detected events to the expected number allows one to derive the constraints on the parameters of muon neutrino oscillations into electron and tau neutrinos. The peculiarity of current situation is in the fact that systematic errors and an error of calculation introduce the largest uncertainty to this ratio. The work is now in progress in order to refine the detection efficiency values and to reduce the calculation errors. As a result of this work, more definite conclusions will be made about possible contradiction with the data of Superkamiokande.
1.2 Nuclear composition of primary cosmic rays. The experimental data on multiplicity spectra of the muon bundles with threshold energies of 0.25, 0.85, 1.3, 2.0, and 3.2 TeV were continued to be processed in order to derive information on the nuclear composition of primary cosmic rays in the energy range 10^13 - 10^15 eV. The previous data did not allow us to make a definite conclusion on the nuclear composition above the knee in the primary spectrum. At the moment we succeeded in advancing to the region of large bundle multiplicities (which corresponds to higher primary energies). The experimental results can be interpreted as heavier nuclear composition after the knee of the primary spectrum. The data of simultaneous detection of extensive air showers (EAS) by the "Andyrchi" surface array (electron component) and by the Underground Scintillation Telescope (muons with an energy of > 0.25 TeV) the mean number of such muons is measured in EAS with the size range 3.10^5 - 3 10^7. These results show a fairly good correlation with the nuclear composition determined by the BUST at lower energies.
1.3 With the "Andyrchi" array, a search was made of gamma-ray bursts with primary energy > 10^13 eV. Fluctuations of the array counting rate are well explained as statistical fluctuations of the cosmic ray background. No candidates for the events of gamma-ray bursts with such an energy have been found after the analysis of correlations of the counting rate with the BATSE events.
1.4 Experimental data on anisotropy of cosmic rays with an energy threshold of 0.25 TeV have been processed for more than 15 years of observation. A good reproducibility of the amplitude and phase of the first harmonic of the sidereal diurnal wave is demonstrated for the entire period of observations.
2.1 At the "Carpet-2" air shower array the events of recording a "delayed component" in the EAS core were discovered with a scintillation detector of 6 m^2 area, placed above the neutron supermonitor. After the passage of an EAS front, the neutron supermonitor detects slow neutrons, the number of which depends on the shower size and distance from the core.
At the same time the scintillation counters detect either fast neutrons or charged particles with a characteristic time of 250 - 300 mcs. This experimental fact can have two explanations:
- the particles propagating with the shower core induce radioactivity in the neutron monitor matter; as a result of prompt decays, the fast neutrons originate that are detected by scintillators;
- the delayed particles are present in the EAS cores. This explanation is much more improbable because of too large values of the delays.
At the moment, a number of test experiments are carried out in order to choose between these two possible explanations.
2.2 At the neutrino channel of the IHEP accelerator (Protvino), around the liquid argon spectrometer BARS, the first stage of the air shower array EAS-BARS with 8 scintillation detectors is constructed and put into operation. First data for 250 hours of exposure are recorded. Processing these data, one can determine the angle of arrival, core position, and the size of an EAS. Currently, the processing of data from the BARS spectrometer (an area of 50 m^2) is under way.
3 In accordance with a cooperation agreement with the Skobeltsyn Nuclear Physics Institute of Moscow University, the research and development works are carried out at the "Carpet-2" muon detector on designing a muon detector for the SHAL-1000 array project.
1. The second tower of joint Russian-Italian detector LVD with 340 tons of scintillator situated in the Gran Sasso Laboratory has been put into operation. The data are collected now from towers 1 and 2 . The third tower is under construction. 2 towers of LVD with about 700 tons of scintillator are the largest detector in the world which combines scintillator and tracking parts. It is constructed for research in neutrino physics, neutrino astrophysics and cosmic ray physics.
2. 40 tons of scintillator have been prepared for scintillation counters of LVD. 690 light shield boxes and 920 dinode chains for photomultiplier tubes have been produced for the LVD third tower.
3. The data collected by LVD, LSD and "Collapse" are used for continuous search for neutrino flux from gravitational collapse of massive stars. Live time of detector operation in 1998 was 95%, 96% and 92% for LVD, LSD and "Collapse", respectively. Analysis of all data sets has shown no candidates to the neutrino burst from gravitational collapse.
3. We performed the analysis of time correlation between satellite-detected gamma-ray bursts and neutrino-like events recorded during 1992 - 1994 with "Collapse" detector. No time correlation has been found.
4. We are doing permanent monitoring of counting rate of LVD detector at 1 MeV energy threshold. We obtained that the counting rate is increased by a factor of two one-two days before an earthquake. The comparison of the data with those from radometer shows that the increase of the rate is due to counting of gammas from the products of radon decays. LVD is sensitive to earthquakes in the circle of radius of 500 km and even more.
5. We have analysed muon events with all muon multiplicities detected by the first LVD tower during more than 900 days of data taking. The depth-intensity relation in the depth range 3000 -12000 hg/cm^2 is obtained. The power index of the primary spectrum is found to be 2.78+-0.05. The upper limit on the ratio of prompt muon flux to that of pions is equal to 2*10{-3} (at 95% c.l.). This limit to the fraction of prompt muons favours the models of charm production based on QGSM and dual parton model.
6. The study of hadron background has shown that LVD is able to detect atmospheric electron antineutrinos and select them from the background at energies up to 250 MeV if space-time distribution of low energy pulses in the time gate of 1 ms after essential energy release in the inner part of LVD is analysed.
7. Arrival directions of single muons collected during 20480 hours by the first LVD tower have been analysed. The Moon shadowing effect has been observed at 2.65 standard deviation level. The detection of the Moon has revealed that the pointing accuracy of LVD is better than 0.5 degrees and the angular resolution is better than 1 degree. To search for point sources of very high energy photons we have analysed muons coming from the directions with different rock overburden (more than 3, 5 and 7 km w. e. which correspond to the mean muon energies at the sea level 1.7, 4.1 and 8.9 TeV, respectively). The upper limits on the muon fluxes from the astrophysical sources CygX-3, Crab Nebula, SS433, 3C273, Geminga, Mrk421, Mrk 501, Hercules X-1 foor different depth regions have been obtained.
8. The analysis of time-correlated events detected by LVD underground and EAS-TOP array at surface has shown that the mean energy of high-energy muons increases with the energy (or size) of extensive air showers (EAS) and the dependence is sensitive to the mass composition of primary cosmic rays. The dependence of the mean energy of muons produced in EAS cores on the EAS size has been measured for the first time. The measured relation favours the mixed composition of primary cosmic rays. The new method of the study of primary cosmic-ray composition has been developed and tested experimentally.
9. It was shown that the gravitational collapse of a star with hydrogen or carbon envelope is accompanied by gamma-ray burst with luminosity of about 5*10^{36} erg. Search for time correlations between gamma-ray bursts and neutrino burst candidates allows the detection of soundless collapse.
In 1998 the group fulfilled the following work on the federal science research and development programme "Research and development on the prior directions of science and engineering advancement of civil purpose on subprogramme "High energy physics":
elaboration of a lithium detector of solar neutrinos, 1996-2005;
development of electronic methods for solar neutrinos detection, 1996-2005.
An Internet site: www.inr.troitsk.ru/~beril has been created.
A manufacture of the lithium detector prototype has been completed and installed at the working area of PEI for testing.
A new method to produce an absorber on the basis of monocrystal LiF for counting Be-7 atoms by means of a cryogenic detector has been put forward.
First samples of absorbers tagged by radioactive atoms Be-7 have been obtained.
1. Collection of data using the Gallium-Germamum Neutrino Telescope continued in 1998. An effort was made to reduce the systematic uncertainties and work started to increase the mass of Ga in the telescope target: the cosmic-ray produced isotope 68Ge was removed from 3.5 tons of Ga and this gallium was added to the target used in recent measurements. Results obtained in the experiment from 1990-1998 show a significant deficit of the overall solar neutrino flux. The average flux measured in the experiment is 68 +/-7 SNU (SNU-Solar Neutrino Unit, I SNU = I neutrino capture per second in a target that contains 10*36 atoms) while the Standard Solar Model (SSM) predicts 129 +/-9 SNU.
Combined with the results of other solar neutrino experiments (chlorine in the USA, water Cherenkov in Japan, and gallium in Italy), the results of theBaksan gallium experiment SAGE present an evidence that neutrinos have mass and oscillate in vacuum or in the matter of the sun, and consequently, present possible evidence of observation of phenomena beyond the so-called Standard Model of Particle Physics. We now appear to be on the verge of one of the most important discoveries in modern physics, which will require revision of our understanding of particle properties.
2. With the goal of additional measurement of the activity of the 51-Cr source that we used to measure the efficiency of the Ga experiment, the mass of V formed in chromium as a result of 51Cr decay was measured. One of the 46 chromium cores in the source was dissolved and the concentration of chromium was determined using emission spectrometry of inductively connected plasma. The V concentration was measured to be 5.6%, from which the source strength was inferred to be 516 kCi at the beginning of the source experiment. This value agreed well with earlier determinations using other procedures.
3. To investigate the possibility of creating a semi- conductor detector based on GaAs, extra pure Ga and As single crystals of semi-insulating GaAs were grown. The Chokhralsky procedure was used to grow the crystals with liquid hermetization of the alloy. The single crystals that were prepared have a hole mobility of electrons at the level of 8000 cm2/V sec and high chemical purity (the impurity content is 10^-7 %). Test detector structures were prepared using the liquid epitaxy procedure. Measurements give values for the specific depth of penetration of the electric field of I mkm/V, and for the life time of free electrons of 6 nsec, which corresponds to the best results achieved anywhere in the world at the present time. In 1999, the development of new technologies is planned to obtain GaAs samples with improved properties, to prepare from this material obtained detector structures, and to measure their characteristics.
4. To investigate the possibility of preparation of an artificial neutrino source of high intensity based on the isotope 37Ar, a pilot installation was created for extraction, purification, and precise measurement of 37Ar activity. This installation allows the extraction of 37Ar from Ca metal and from a number of Ca-containing compounds. The foundation of the technology for extraction of 37Ar from Ca targets irradiated in fast flux nuclear reactors has been developed using this installation.
5. The flux and energy spectrum of fast neutrons in the most deep low background laboratory at the Baksan Neutrino Observatory have been measured. In the region of neutron energies 0.7-12.0 MeV, the flux is (9.5 +/- 2.6) 10^-7 neutrons/cm^2 sec. Measurements of the activity of different types of selected mountain rocks for reduction of the fast neutron flux have also been carried out. These measurements show that serpantinit gives the most effective protection. The spectrometer sensitivity for low fluxes of fast neutrons is several times higher than the best detectors of this type presented in the literature.
Most important achievement:
The Gallium-Germanium Neutrino Experiment SAGE continues its measurements of the neutrino radiation from the Sun that were started in 1990. The observed flux of solar neutrinos is about 53% of the value predicted by the Standard Solar Model. Combined with the results of other solar neutrino experiments (chlorine in the 'USA, water Cherenkov in Japan, and gallium in Italy), the results of the Baksan gallium experiment SAGE present serious indication that neutrinos have mass and oscillate in vacuum or in the matter of the sun, and consequently, that we possibly observe now a phenomena not predicted by the most modern complete theory of particles a so-called Standard Model of Particle Physics. We now appear to be on the verge of one of the most important discoveries in modern physics, which will require revision of our understanding of particle properties.
"Neutrino telescopes in the World Ocean (optical and acoustical ones) and in the deep ice of the Antarctica (radio wave one)"
1. Development and construction of the deep underwater optical neutrino telescope NESTOR in the Mediterranean Sea for registration of cosmic neutrinos with energies greater than 10 GeV. Produced together with the Experimental Design Bureau of Oceanological Techniques of the Russian Academy of Sciences a mechanical construction of the second floor of the neutrino telescope NESTOR consisting of 18 5-meter titanium sections, is sent to Greece for deep underwater tests in the Mediterranean Sea. A program for the fast simulation of the Cherenkov light from electromagnetic cascades is performed. The CPU time has been reduced in 10^6 times for the showers with energy 10^5 GeV.
2. Development and construction of the deep underwater acoustic neutrino telescope SADCO for registration of cosmic neutrinos with energies greater than 5*10^15 eV. The acoustic emission of hadron and electron-photon cascades produced by cosmic neutrinos with energies 10^20 - 10^21 eV in water has been calculated. Essential peculiarity of the acoustic signals from electron-photon cascades produced by electron neutrinos is connected with the Landau-Pomeranchuk-Migdal effect which increases much the longitudinal sizes of these cascades. INR together with the Andreev Acoustic Institute (Moscow) and "Morfizpribor" (St. Petersburg) have studied possibilities of detection of the acoustic signals from electron-hadron cascades produced by superhigh energy neutrino (10^20-10^21 eV) in water mass of the ocean with help of a stationary hydroacoustical antenna lattice placed in the northwest of the Pacific Ocean. Numerical modeling of the acoustic fields generated by neutrinos (cascades) at large distances from interaction points under different season conditions is carried out. It is shown that (even in nonoptimal for registration of the cascades frequency band of the existing antenna system) an acoustic detector of superhigh energy neutrinos with the detection volume up to 0.75-5 km^3 in dependence on hydrologoacoustic conditions and observation period can be realized.
3. Elaboration of the project of a radio wave neutrino telescope in the Antarctica. Research works on construction of a radiowave neutrino telescope in the Antarctica (at South Pole) together with the Cansas University, USA (project RICE) are continued. Seven antenna channels for the pilot system RICE are manufactured. Tests are planned to be made in this winter season.
4. Development and construction of novel scintillators and luminescence substances. A sample of the liquid scintillator containing 12 weight per cent of Gadolinium is made. The scintillator has a high scintillator efficiency, transparency and stability and can be recommended for solar neutrino detector. A sample of the liquid scintillator containing the complex compound of circonium (8 per cent of metal) is made.A Russian patent on the scintillator has been issued. The scintillator can be used for investigation of double beta-decay. A business-plan for creation and production of the luminescence substances in Russia which are high transparent to their own radiation is ellaborated together with Institute of physical and organic chemistry of Rostov-on-Don University. Such luminescence substances can be used both in liquid and plastic scintillators.
5. Avalanche MRS-detector for scintillator counters. In 1995-1998 INR RAS together with JINR, Dubna developed a new approach to the construction of the solidstate analogs of PMT - single photon counters. The new method is based on using an avalanche process into the multilayer MRS-structures (metal-resistivity layer-semiconductor). Tests of a sample of the avalanche MRS-photodiode with a sensitive area (0.5*0.5) mm^2 and with a gain coefficient greater than 10^4 showed that single photons can be registered at a room temperature with a probability 23 per cent (within 100 nsec).
INTENSITY OF PROTONS WITH ENERGY ABOVE 500 GEV DURING GLES
An analysis is carried out of three significant bursts of muon intensity recorded at the Baksan Underground Scintillation Telescope on September 29, 1989, June 15, 1991 and October 12, 1981. The muon intensity and corresponding intensity of primary protons which produced those bursts are calculated. We estimated an integral energy spectrum of relativistic protons for event of September 29, 1989. The results make the very peculiar and strict requirements to possible particle source(s), acceleration and propagation mechanisms. It is suggested that the observed effect is closely linked with the powerful solar processes, implying possible impact of extended coronal structures (larg loops, streamers, coronal shocks etc.), coronal mass ejection, heliospheric current sheet.
Lift of the deep underwater detector NT-144, repair and replacement of its failed equipment were performed during the 1998 winter expedition to the Baikal Lake. Additional 48 optical and 16 electronic modules were deployed.
Since April 1998, the upgraded neutrino telescope NT-200 which contains 192 optical modules has been under operation. A deployment of an additional cable which connects the detector site with the shore station has been performed. The new more reliable power sources are installed in the most part of the optical modules.
At present about 1.7*10^8 atmospheric muons were detected by NT-200 for 190 days of data taking. The rate of neutrino induced events appeared to be equal to about one per day. Calibration of time and amplitude measuring channels of neutrino telescope NT-200 has been performed. The electronic time shifts of the channels have been obtained using the data of optical and fiber lasers and after the analysis of the events induced by vertically moving atmospheric muons.
After analysis of 4.5*10^7 experimental events which were taken from April till July, 1998 a pure sample of events for the following reconstruction has been established. A combined upper limit on the flux of fast monopoles 6*10^{-16} cm^{-2}sec^{-1}str^{-1} has been obtained from the data taken with neutrino detectors NT-36 and NT-96, which is now one of the best experimental limits. The specialized two channel PMT for using in the QUASAR-370 photodetector has been developed and created. It has a time resolution of 0.3 nsec and a level of cross talks between channels of about 2%. On the base of this PMT the two channel optical module is being prepared to be testedunder natural conditions at the Baikal Lake.
A prototype of the QUASAR-370 photodetector with semiconducter diod as an multiplier has been created.
The BAIKAL collaboration includes the following Russian and foreign departments: Institute for Nuclear Research (Moscow), Irkutsk State University, Moscow State University, Nizhni Novgorod State Technical University, St.Petersburg State Marine Technical University, Joint Institute for Nuclear Research (Dubna), Kurchatov Institute, DESY Institute for High Energy Physics (Zeuthen, Germany), Acoustical Institute (Moscow).
1. "Experimental physics" (Experiments at MMF)
As a result of study of reactions p+d->p+d+(gamma) and p+d->p+p+(gamma+n) at 305 MeV two narrow structures in missing mass spectra at 1905 and 1924 MeV with widths equal to the experimental resolution 3 MeV were observed. The comparison of the experimental yields with the Monte Carlo simulations showed that the found peaks can be explained as the supernarrow dibaryons the decay of which into two nucleons is suppressed by Pauli principle. The shape of an angular dependence of the charged particles emitted from the decay of the dibaryon with mass 1905 MeV agrees well with the calculated curve for dibaryon D(T=1, JP=1+, S=1) or D(1, 1-, 0).
2. "Experimental physics" (Experiments at ITEP)
For the first time emission of light charged particles (LCP) from fragments of uranium fission by 1700 MeV pions was observed. The isotropic angular distribution of LCP makes it possible to suppose that they are emitted from non-accelerated fragments. (Earlier at lower energies of incident particles the emission of LCP from accelerated fragments only was observed only.) Such a process is possible when the fission of a strongly excited proton-rich nucleus (formed at the cascade-evaporation stage) proceeds rapidly enough.
3. "Theoretical physics"
Theoretical description of the s-, p- and d-wave neutron strength function and potential scattering lengths of s- and p-neutrons is obtained for even-even spherical nuclei with 56<=A<=206 in the framework of the unified approach proposed earlier for the description of low-energy neutron interactions with such nuclei. The d-wave strength functions and the potential scattering lengths of p-neutrons are reproduced for the first time. It is shown that this approach allows one to describe the totality of low-energy neutron data and to calculate neutron cross sections and strength functions of the nuclei for which direct measurements are extremely difficult.
4. "Applied physics"
A hypothesis for the impact of natural alpha-radiation of uranium and thorium decay on the enhanced diffusion of gas-forming elements into mantle-originated crystals of age exceeding 400 millions years is proposed and confirmed experimentally. A numerical simulation on olivine crystals using the nuclear reaction 12C(d,p)13C has shown (at deuteron doses equivalent in defect formation to alpha-particles) enhancing the carbon diffusion into the crystal depth even at T=370K. A confirmation of the found data for other gas-forming elements can lead to correction of the conventional concepts gas conditions of the Earth and its degasation mechanisms.
Theory
Results have been obtained indicating the absence of Coulomb energy anomalies, known as Nolen-Shiffer effect, in the isotopic multiplets of 6-nucleon system (6He-6Li) in terms of the multicluster dynamic model with antysymmetrization.
Polarization properties of 6Li nucleus in electron scattering are analysed within framework of the multicluster dynamic model with antysymmetrization. More precise results obtained than those predicted by standard shell model due to the fact that multicluster model takes into account the nucleon correlations in more detail.
Theoretical calculations performed within the framework of the non-relativistic two-step model lead us to conclusion that the experimental observation of the eta' and phi-meson production in reactions pd -> d eta' p(sp) and pd -> d phi p(sp) cannot be performed by means of missing mass analysis of final deuteron and spectator proton. It's necessary to detect the products of the eta' and phi mesons decay.
Experimental Physics
An activity has been continued on the project "Study of spin depending phenomena in the spontaneous fission of polarised actinide nuclei". A nuclear orientation thermometer for the NORD-2 facility was prepared. Semiconductor detectors of charged fragments were calibrated at the liquid helium temperature. Elements were constructed of a Helmholtz superconducting magnet which makes possible the multichannel measurements of fragments angular distributions.
To determine the contribution of the isovector electric quadrupole giant resonance the study of the forward-backward asymmetry of photoneutrons is suggested. To perform the appropriate investigations some parts of neutron spectrometer has been made, the design of time-of-flight part of this spectrometer is completed. The gaging equipment for the background studying is prepared. To calcu- late the above mentioned asymmetry on a base of finite Fermi-system theory the set of certain programs is created and debugged.
The mechanism of the photoabsorption by nucleons and light nuclei in the 200-800 MeV energy region and a contribution of meson effects to photonuclear sum rules(SR) were studied using recent data. It is shown, that the mechanism is analogical in a region from the nucleon upto heavy nuclei and corresponds to the volume non-coherent photoabsorption, like if a nucleus interacts as a sum of free nucleons with small correction effects of nuclei interaction. In spite of the generally accepted point of view of a small redistribution of the photoabsorption strength (order of 4%) occures between delta- and 2nd baryon resonances. New theoretical approaches are demanded. The photonuclear SR were fruitfully used during the long time for a study of nuclear properties. It was experimentally found,that the classical SR should be increased up to the meson threshold for a factor of (0.3 - 0.7) from deutron to heavy nuclei. The Bete-Levinger and Gell-Mann et al. theories have explained such an increasing by meson effects, numerically by an contribution of a pion photoproduction from the delta-resonance region (150-450 MeV). According to the recent data, this interval does not contribute to the SR significantly.
The experiments on foreign Institutions accelerators
MAMI accelerator.
Experimental data analysis for measurement of elastic scattering of photons on the proton for the wide angle range by means of LARA detector was continued. There were received preliminary results for cross-sections at the energies 260-760 MeV for scattering angles 60-150 degrees. These results point out disagreement with existing calculations at large scattering angles. Now detailed analysis of possible systematic errors of experiment is carried out.
Experimental data analysis for measurement of photon scattering on the proton at low energies for wide angle range using the photon spectrometer TAPS for was continued for receiving of more accurate values of fundamental constants of electric and magnetic polarizabilities of the proton and for receiving pion photoproduction cross-sections near threshold. There were also received cross-sections for double photoproduction of neutral pions and eta-mesons.
Main efforts were directed on carrying out of the first stage of the experiment for investigation of the nucleon spin structure at the MAMI accelerator with using of circularly polarized tagged photons and longitudinally polarized nucleons in a frozen-spin target. In the beginning of this year there was finished modernization of the set of experimental systems and the construction of polarized target was improved. Circularly polarized photons are produced by bremsstrahlung of longitudinally polarized electrons with a degree of polarization of about 75 %. Nucleon polarization up to 87 % was achieved in the butanol frozen-spin target. Dynamical nuclear polarization takes place in a horizontal dilution cryostat at T=300 mK and magnetic field B=2.5 T. The polarization is maintained during measurements in the frozen-spin mode at T=50 mK by internal superconducting coil (B~0.35 T). Typical relaxation time is about 200 hours. During 1998 May-August measurements of the helicity dependence of total and partial photon-nucleon cross-sections at initial electron energies 525 and 855 MeV using 1500 beam-time hours were carried out. Preliminary analysis of these data shows that valuable information on the nucleon spin structure is obtained what allows us to test the Gerasimov-Drell-Hearn sum rule and to find firstly measured value of forward spin polarizability.
GRAAL collaboration
First results on the beam asymmetry for eta-meson photoproduction on the proton have been produced from the threshold to 1100 MeV in a wide angles range of 30-170 deg. At the energies below 900 MeV the new experimental data confirm the theoretical predictions, while above this region the measured asymmetries are significantly larger at forward angles. It indicates an important contribution of higher spin resonances, like F15(1680), F35(1905) and F37(1950) which are not accounted in the previous calculations. It might be also a manifestation of ``missing'' resonances, predicted by QCD, but not yet observed.
High precision experimental data on the beam asymmetry for positive pion photoproduction on the proton have been obtained in a wide angles range 40-160 deg from 550 to 1100 MeV. New experimental points cover the almost unmeasured region of backward angles. The results exhibit the smaller contribution of the F15(1680) nucleon resonance, than it was treated by the group of Virginia Polytechnic Institute (USA), whose partial wave analysis solution for single-pion photoproduction amplitudes is now used in a wide number of applications.
The upper limit of probability for production of low mass nucleon resonances (between free nucleon and Delta) have been measured in the reaction of photoproduction of positive mesons on a free nucleon. This work was stimulated by recent results from Orsay where such resonances were evidenced for proton induced reactions. The paper on this subject is performed by russiun side and it is in discussion of collaboration now. The result shows that probability of excitation of low mass nucleon resonances does not exceed 0.2% as compared with the positive meson production partial cross section. The analysis demostrates the low backgrounds of the GRAAL facility and favorable possibility to study the rare processes in photonuclear reactions at intermediate energies.
To develope future experiments the rusiian part performed simulations of photoproduction of heavy mesons on nuclei (bound nucleons). The intranuclear cascade code was applied to various photoproduction channels including pions and eta-meson production. The unexpected result leads to the new approuch ("tagged mesons") which is based on the correlation measurement of the primary recoil nucleon and secondary interaction products. The primary recoil nucleon as a tagger for respective mesons is identified by special kinematics analysis. Concrete calculatios have been performed for interaction of eta-mesons with a nucleus 14-N. It is shown that the necessary experimental conditions (large solid angle, identification of secondary products, low backgrounds) can be realised at axisting facilities as GRAAL basing on the low background back scattered laser beams. This approuh opens a promissible way to study interaction of unstable mesons with nuclear media.
In the framework of DELTA-SIGMA experiment (JINR - INR RAS - Gatchina - Kharkov -CEA/Saclay collaboration) a construction and tests were finished of a superconducting magnetic system which provides a transverse spin polarisation of the Movable Polarised Target (MPT). A testing run at the polarised neutron beam of JINR synchrophasotron was performed for tests and calibration of the detecting system. A processing was finished of the measurement results of energy dependences of the total cross section differences for a transmission of polarised neutrons through the polarised proton target at longitudinal beam and target polarisations in 1.2 - 3.7 GeV neutron energy range.
In the framework of JINR - INR RAS - Kharkov - Prague collaboration works were done on the project "Experimental study of np and nd elastic scattering amplitudes at 16 MeV". A testing run with the deuteron polarised target and an upgraded neutron detecting system was performed at the accelerator of the Charles University (Prague).
The development of scienific complex of Institute.
RM-175 Race-track Microtron.
The first version of the experimental research program for 175 MeV CW racetrack microtron, which is now under construction at INR, is completed. On the base of analysis of nuclear theory needs and present status of experimental investigations the study of C0, C1 and C2 giant resonances excitation and decay in (e,e'X ) coincidence experiments is suggested as the main subject of research.
The program is delivered as INR internal report and is now prepared to be published as INR preprint.
Possibilities of designing of klystron output parameters stabilization system were studed using klystron focusing electrode voltage automatic control.
Increasing of RF stand output power up to 12 kW was achieved. Investigations of klystron dynamic parameters dependence on various destabilizing factors at maximal output power was studied.
Applied Physics
Possibilities of short-lived radioisotopes production for medical aplications with new generation electron accelerators on the base of non-expensive compact high current pulsed microtrons were analyzed in comparison with the case of heavy-particle accelerators. It is understood that electron accelerators are good tools for the production of short-lived radioisotopes for Positron Emission Tomography (PET).
Together with Moscow State University the activity was continued on the project "A study of materials with new properties using nuclear methods based on alpha- and gamma-radiation detection". Mossbauer studies of FeNiMn alloys having different magnetic structures have been performed.