The Main Results
of Fundamental & Applied Researches for 2000.
A new possibility that a presence of additional dimensions is
playing role not only in the short range and high energy physics
but also at large distances, at large time intervals and at low
energies was revealed in theories with more than four time-space
dimensions. In this case processes non-conserving energy and electric
charge from the four-dimension point of view are possible.
One of such processes is the electron decay into invisible mode
(experimentally indistinguishable from the electron decay into three
neutrinos), which has a small but non-zero probability in
multidimensional theories. This result makes possible a search for
signals of additional dimensions in rare processes of particle
physics and in cosmology.
A detailed analysis has been done of the Tevatron experimental data for structure functions of deep inelastic neutrino-nucleon scattering. Values of the QCD constant were derived and effects of the highest twists were analyzed.
An analysis of the anti-t, t-quark production near the threshold was performed. By means of sum rules the b-quark mass was determined with a high accuracy. An effective electromagnetic constant was calculated and its effect on determination of the Higgs boson mass was studied.
Combined results on nu_mu - nu_tau oscillations and nu_e scattering from the SUPER-KAMIOKANDE and LAMPF experiments, respectively, limit the Dirac nu_tau diagonal magnetic moment to <1.9*10^{-9} mu_B. For the scheme with 3 Majorana neutrinos the LAMPF results allow the limitation of effective nu_tau magnetic moment to <7.6*10^{-10} mu_B.
There was proposed a new mechanism of matter production due to vacuum fluctuations in the early Universe.
New experimental data on anomalous charmonium suppression in lead-lead collisions at ultra high energy were obtained in agreement with the previous data obtained by NA50 collaboration with INR RAS participation.
For the most central events at the highest energy density sharp suppression of the charmonium production was observed
These results along with the discontinuous behavior obtained at lower centrality support the conclusion about the sequential suppression of psi', hi_c and J/psi charmonium states in Debay screening mechanism if quark-gluon plasma is formed in the collision.
Transverse momentum distributions of the J/psi, psi', Drell-Yan and the intermediate mass continuum were investigated. Mean values of the transverse momentum and the square of the transverse momentum were obtained and for the J/psi also the inverse slope parameter T as a function of the centrality of collision was obtained. The data are in agreement with the initial parton interactions model. ( INR RAS, NA50 ).
In 2000 the first physical results of the measurement of the K+ -> pi0 e+ nu (K_e3) decay form-factors were obtained. The value of the lambda+ parameter from the dependence of the vector form-factor on the four-momentum transfer squared is determined. The value obtained lambda+ = 0.0278 +- 0.0026(stat) +- 0.0030(syst) is in a good agreement with the results of the previous experiments (see PDG: Eur.Phys.J C15(2000) p.506).
It should be noted, however, that the search for the exotic (scalar and tensor) interactions could not confirm the previous result obtained in the work by S.A.Akimenko et al. (Phys.Lett 259B(1991)225), where non-zero scalar and tensor form factors deviating from zero by 3.6 and 3.4 standard deviations, respectively, were found. In our experiment the comparison of the experimental Dalitz-distribution and the Monte-Carlo simulation data leads to the zero values of the scalar and tensor couplings which is consistent with the predictions of the Standard Model:
f_s/f_+0 = -0.002+-0.026(stat)+-0.0014(syst)
f_t/f_+0 = -0.01+-0.14(stat)+-0.09(syst)
At the present time an analysis of the large data sample of the K_e3 decays by means of several methods is in progress.
To search for supernarrow dibaryons (SNDs) an analysis of experimental data on the reaction pd->pX, obtained at the INR Proton Linear Accelerator in the end of 1999 , has been carried out. In missing mass spectra of this reaction picks at M=1904 +- 2, 1926 +- 2, and 1942 +- 2 have been observed with numbers of standard deviations 6.0, 7.0, and 6.3, respectively. The first two of these picks confirm the values of the dibaryon masses we obtained earlier and the resonance at 1942 MeV is a new one. The analysis of the angular distribution of the protons from decay of dibaryons shows that the found dibaryons are likely to be SNDs, the decay of which into two nucleons is forbidden by the Pauly exclusion principle. In missing mass spectra of the reaction pd->ppX_1, three resonance-like states have been found, the mass values of which correspond to the decay of the observed dibaryons into gammaNN. This is an additional confirmation that the found dibaryons are SNDs. As these dibaryons decay mainly in the gammaNN channel, it is reasonable to suggest that all of them are isovector SNDs (INR RAS, LPI RAS)
A pre-shower detector of the LHCb set-up has been elaborated. Detector pilot modules have been manufactured and tested in CERN.
A module of the front electromagnetic calorimeter of the CMS set-up (LHC, CERN) on the basis of PWO crystals has also been successfully developed, manufactured and tested.
In the frame of the HADES collaboration ( wide aperture magnetic spectrometer, GSI, Germany) INR RAS developed and constructed the time-of-flight system of detectors which covers the polar angle forward region from 13 to 45 degrees. The aim of this detector is to provide the first level reaction trigger for multiplicities and increase the efficiency of electron identification by the shower detector. The system of detectors was tested and installed in the HADES apparatus. Measurements were made on carbon beam at GSI. The obtained experimental data are being analyzed now.
A project of the new central trigger detector for ALICE ( LHC, CERN ) with quarts emitters was prepared. The best time resolution of about 45 picoseconds was obtained for test beam measurements. Optimization of the multiplicity detector on the base of the silicone detectors was made (INR RAS, MEPhI, ALICE ).
An inclusive production of meson resonances in the neutrino interactions has been studied at the NOMAD detector at CERN. We were the first to observe the production of the f_0(980) meson state at the 6 sigma confidence level. Presence of another state f_2(1270) is reliably established.
For the first time existence of the axion in the mass range of 1-100 eV is constraned with the NOMAD detector based on the photon regeneration method also used for the first time at high energies.
The limit for the probability of muon neutrino to tau neutrino oscillations is pushed down to the level of ~2*10^{-4} (90% C.L) at large delta m^2 by the new improved analysis of the NOMAD data. This limit is more than a factor 3 better than the previously published ones.
For the first time systematic investigations of the light charged particles (LCPs) emission from the fragments of uranium nucleus fission by the particles of different nature (muons, pions and protons) in the wide interval of energies (10 - 1700 MeV) have been carried out. The probability of LCPs emission increases strongly with energy (from 10^{-5} to 1). New peculiarities of this process have been found. In the fission with particles of low energy LCP are emitted from the light accelerated fragments (non-isotropic in l.s.), but in the fission with 150 MeV particles LCPs are emitted from the heavy accelerated fragments (non-isotropic in l.s.). At the energy of particles not less than 1000 MeV there are substantial changes of the LCP emission mechanism: they are emitted from the non-accelerated fragments or probably at the earlier stage. In that case the LCPs can provide new data about the last stage of the fission process. The neutrons are always emitted from the accelerated fragments thus not giving such information (INR RAS).
Total and differential cross sections for photoproduction of eta mesons from the threshold to 1100 MeV have been measured (GRAAL collaboration). For the first time, the region of S11(1535) resonance is fully covered, allowing a precise measurement of its width. It is shown that above 900 MeV, S-wave dominance disappears while P - and D - waves take over.
Compton scattering by the proton has been measured in the first and second resonance regions. The experiment was carried out using the tagged-photon facility at MAMI (Mainz) and the large-acceptance arrangement LARA by the A2 collaboration where INR RAS participates.
An experiment on examining the production of high-spin isomeric states in the reactions of protons with tantalum nuclei has been completed.
New conformities have been discovered ( the dependence of the isomeric relation production cross-section on the spin value and proton energy ) which entailed the review of the existing theoretical models.
In 2000 during the winter expedition at lake Baikal lifting of the NT-200 array from the depth to the surface was performed, analysis of the apparatus state was done and partial renewal of the deep underwater equipment was carried out at neutrino telescope NT-200 which was assembled and put into operation in compliance with the technical design conditions in March - April 1998. Starting from 11 April 2000 and hitherto the detector has already been operating for 185 days in the mode of data acquisition and storage.
62 million events induced by the cosmic ray muons were already detected and proved to be spatially reconstructed. The count rate for the muons produced by atmospheric neutrinos is approximately 1 event per 2 days so in this regard the Baikal Neutrino Telescope is one of the world's largest working telescopes.
On the base of the data obtained with the help of the NT-200 detetor during its operational cycle from April 1998 till February 1999 new stringent limits on the natural flux of fast magnetic monopoles, the muon flux from massive dark matter particles annihilation in the Earth core and on the diffuse flux of high energy (E>10 TeV) neutrinos were established.
The analysis of the measurements of solar neutrino flux taken on the underground Gallium-Germanium Neutrino Telescope of the INR RAS for the period of 10 years gives the value of the flux a little bit greater than the half the value predicted by the Standard Solar Model which testifies the fact that the flux of solar neutrinos with the energy less than 2 MeV reaching the Earth is essentially suppressed.
The result obtained indicates the existence of new properties of neutrino-neutrino oscillations which change the flavor of solar neutrinos on their way to the Earth and make it possible to detect a large fraction of them by the Gallium-Germanium Neutrino Telescope.
The evidence of the existence of neutrino oscillations and, therefore, the existence of neutrino mass will require the crucial change in the notion of the elementary particles properties as well as up-to-date understanding of the origin and evolution of the Universe.
The analysis of many-year observations at the Baksan Underground Scintillation Telescope gave the spectrum of multiplicity of muons in groups for the depth of 5000 g/cm^2 and threshold energy of 3/2 TeV.
On its basis one of the best world estimation of the nuclear composition of the primary cosmic emission within the energy region 10^15 - 10^16 eV has been obtained.
Calculations have been carried out for the spectrum of the primary cosmic emission with a constant index as well as for the spectrum with a bend at 3*10^15 eV.
The data is consistent with the bend at the fixed energy per nucleon and is inconsistent with the bend at the fixed energy per nucleus.
The effective atomic number within this region is 5.4 which is a bit greater than the expected figure (4.9).
The largest scintillation detector LVD ( Large Volume Detector ) started running in the Gran Sasso Underground Laboratory ( Italy ) in 2000. It contains more than 10000 tons of liquid scintillator interleaved with limited streamer tubes in a compact geometry. The detector has a modular structure which consists of 3 towers. The scintillator and modules-detectors were elaborated and manufactured in INR RAN.
LVD experiment is an underground observatory mainly designed for scientific research in neutrino astronomy, cosmic-ray physics, search for point sources of high-energy neutrinos and gammas, neutrino oscillations and study of rare processes predicted by the theory.
In 2000 the Moscow Meson Factory Linac (MMFL) provided eight accelerator shifts, totally 1800 beam hours for physical experiments and isotope production for medicine. The maximum beam energy was limited to 305 MeV for economical reasons.
The upgrade of the injection line including installation of a new booster RFQ enabled one to essentially improve the reliability of the accelerator as well as to increase the beam intensity. The maximum average beam current equals 150 microA. A long term operation is provided with the current of 120 microA and total beam losses less than 0.1%. The integral intensity for 12 hours is about 1000 microA.
Modernization of the MMFL automatic control system started in 2000. The upgraded control system is based on personal computers networked with the control systems of the experimental and medical facilities. The first stage of the new control system has been put into operation.
The modernized control system of the accelerator is based on personal computers.
The interface with the equipment is provided via industrial input/output interface boards produced by National Instruments Company.
The study of the method of production of polarized negative hydrogen ions due to resonant charge-exchange between polarized hydrogen atoms and unpolarized negative deuterium ions in deuterium plasma continued in 2000. The density of the negative deuterium ions in plasma was increased four times thus resulting in increasing the pulse current of negative hydrogen ions from the source up to 2.5 mA with the pulse length of 150 microsec and repetition rate of 10 Hz.
The method of production of polarized negative hydrogen ions due to resonant charge-exchange between polarized hydrogen atoms with thermal energy and unpolarized negative deuterium ions in deuterium plasma was developed in INR earlier. The efficiency of the method was improved in 2000 due to increasing of the density of the unpolarized negative deuterium ions. A two-stage deuterium plasma converter has been developed: initially the deuterium ions are converted into neutral "hot atoms" and then into negative ions on the surface with low work function. The intensity of the negative hydrogen polarized ion beam from the source exceeds a world level achieved so far.
In December 2000 a unique 100-ton supersensitive lead neutron slowing down spectrometer was launched in INR RAS. It belongs to the spectrometers of the third generation where neutrons are produced through spallation process (caused by the proton beam of the linear accelerator of INR RAS). The very first experiments showed that its resolution is close to the theoretical one (~ 26%) and is about 30%. The research energy region is now as wide as 1 eV - 30 KeV.
The spectrometer is intended to be used in the field of fundamental and applied physics as well as radiation medicine.
Owing to the performed experiments neutron spectra have been obtained, a spectrometer resolution has been estimated and an energy region and neutron fluxes have been determined. Studies of (n, gamma) reactions on Cu, Mn, Co, S, Bi,V, Sb and fission reactions on U^235, Pu^240 have been fulfilled.
According to the agreement on scientific collaboration between INR and TRIUMF, Canada, four triple-gap "split-ring" bunchers for the accelerator of radioactive ions ISAC have been developed and fabricated. The bunchers operate in a continuous mode at a power level of 3.5-8.8 kW at a frequency of 106.08 MHz. The bunchers have been tuned and tested on site with nominal power.
DESY was the first in the world to create a free-electrons laser possessing unique parameters.
Elaboration of the technical proposal of the magnetic optical system of the positron beam injection channel of the linear collider TESLA has been completed.
In collaboration with INR a record level of the accelerating field in the superconducting resonators at a frequency of 1.300 MHz - 45 MV/m was obtained in DESY.
A method to produce medical radionuclide palladium-103 and to clean it from radionuclide impurities was developed at MMF, RAN. It is being tried out in the production process at the Institute of Chemical Physics named after Karpov ( the town of Obninsk ).
A project of the Proton Therapy Complex has been elaborated on the basis of the MMF proton accelerator. Equipment for diagnostics of the low-intensity proton beam system has been developed and manufactured.
A method has been developed for determining depth profiles of elements in nanostructures and film-substrate interfaces in the nanometer range (5-100 nm). To reconstruct concentration profiles of elements from heavy ion energy spectra, the BEAM EXPERT package was updated. The method potentials were demonstrated by the examples of analysis of Au/Si Schottky contacts and Pb-Si ion-implanted layers at normal incidence of the ^14N ion beam of energy 0.8 MeV and using a Si-semiconductor detector of heavy ions with 28-keV resolution. Record-breaking (for semiconductor spectrometry) absolute and relative depth resolutions were attained: 1-2 nm and 0.01, respectively. In the case of sliding geometry the resolution is improved to 0.2-0.4 nm (INR RAS).
In collaboration with JINR ( Dubna ) INR has developed, manufactured and tested the samples of new avalanche silicon MRS (metal-resistivity layer-semiconductor) photodiodes with an area of 1 mm and 8 mm and operational voltage of 60-90 V which are able to detect very weak light pulses to the point of isolated photons.
Taking into account such parameters as a gain coefficient (>2*10^3) and a width of the spectral sensitivity area ( 250-900 nm ) the MRS-photodiodes are considered to be much better than the analogous avalanche photodiodes of the famous foreign firms: Hamamatsu (Japan), Advanced Photonics (USA) and others.
The MRS- photodiodes can be used in construction of multi-element high sensitivity photoreceivers for fundamental and applied studies, in particular, positron-emission tomographs of a new generation.
A project has been prepared of the electron linac based complex for sterilization of medical instrumentation and radiation processing of industrial articles and materials.
A computer-aided system for transportation of the exposed pieces has been created.