Skobeltsyn Institute of Nuclear Physics
Lomonosov Moscow State University

Laboratory of experimetal elementary particles physics

The Laboratory of experimental elementary particles physics (LEEPP) was extablished in 1978 as a part of the Deaprtment of measurement technology, which in 1987 was renamed into the Deaptment of experimental high-energy physics (DEHEP). Professor, DSc. Pavel Ermolov was the first leader of the Laboratory. Currently it's Head is PhD. Lev Dudko.

At the beginning of its activity the Laboratory carried out studies in the following scientific directions: development of new methods for elementary particles detection and experimental equipment, software development for analysis of experimental data, experimental data analysis using models and comparison with theoretical predictions.

In 1970-80s automated complexes for analysis of the data obtained by large bubble cameras and hybrid spectrometers were developed. Due to universal measuring and calculating complex developed in 1981-1983 SINP MSU was offered to take part in the research conducted on the base of the European hybrid spectrometer (EHS, CERN). EHS is a wide-aperture spectrometer with advanced calorimetry system and charged particles identification system. It was exposed in the beams of SPS CERN accelerator at the protons energies of 250, 260 and 400 GeV (experiments NA-22, NA-23 and NA-27). About 20 Universities and scientific centers of Europe, India and Japan took part in this research. In 1980-90s EHS was one of the largest plants in the field of studies of different points of multiparticle production at high energies and one of the last plants with bubble cameras, because “the era of bubble cameras” was finishing. In SINP MSU processing of the data of NA-23 eperiment began simultaneously with start of the operation of measuring equipment PUOS-4 operated in line with EC-1045 computers. Accuracy of measurements and determination of track parameters was analyzed in details and compared with data obtained in IHEP (Protvino) and Insbruck and Tokio Universities. As a result cross-sections and spectra of charmed particles at the energies ober 100 GeV were measured for the first time. A number of studies concerned separation of strange particles and resonances, correlation of particles during multiparticle production. Data obtained by EHS were used for the development of theoretical models and methods of simulation of multiparticle production, such as PYTHIA, FRITIOF, DTU, LUND, MKGS. Data of NA-22 experiment obtained using beam of K+-mesnons at the energy of 250 GeV stay unique till present, because beams of K+-mesons with energy over 250 Gev were not produced yet.

In 1984 collaboration of IHEP, JINR, SINP MSU and IHEP TSU offered and developed a project of a large experimental plant – spectrometer with vertex detector (SVD) for measurements of near-threshold production of charmed particles at the energy of about 70 GeV at U-70 accelerator (Protvino). Scientists of SINP MSU have developed design of proportional cameras with size up to 1,5 m for coordinate measurements of particles trajectories with accuracy up to 1 mm and complex of on-camera and recording equipment and fast trigger system. The system was successfully assemebled and is operated at the proton beams of U-70 accelerator. It consisted of fast-cycled bubble camera as a vertex detector, monitoring and tiggering system, magnetic spectrometer and photon detector. It has over 20 thousands recording channels operated in line with computers and specialized processor for event selection and data acquisition control. About 40 articles described the equipment, experimental methods and physical results were published by SVD collaboration. The first session of statistics acquisition took place in 1992, about 180 events were recorded. Only ~40% of them happened in the operation volume of the camera and about 30% of the events did not have spectrometry information. The second session took place in 1994. In 1996 the second stage of SVD experiment was started with changing of bubble camera with an active target, consisted of the carbon, silicon and lead plates and precised fast-response vertex detector (PVD) based on microstrip silicon detectors with 10 000 of recording channels. At that moment PVD of this type was developed in Russia for the first time. By 2011 about 52 millions of non-elastic pA interactions at the energy of proton beam of 70 Gev and about 50 millions of pA events at the energy of 50 GeV were recorded at SVD-2. The properties of charmed D-mesons and their A-dependence were studied, an exotic five-quark barion θ+(1530) with positive parity and strangeness equal to +1 was separated during production of strange mesons and barions. In 2003 a project “Thermalization” offered by scientists from Dubna was carried out at the plant SVD-2. In this experiment topological cross-sections up to 30 charged particles were measured during pp-interactions at the energy of protons 50-70 GeV by means of liquid-hydrogen target in order to study the properties of hadronic system with high pion density.

At the beginning of 1990s the scientists of the Department took part in the high-energy physics experiments of next generation. The experiments with large bubble cameras (MIRABEL at U-70 accelerator IHEP, EHS-RCBC at SPS accelerator of CERN) were changed with the experiemtns based on electronic detectors of elementary particles.

Participation of some LEEPP scientists in the experiment ZEUS at electron-proton collider HERA (Hamurg, Germany) was fairly predestinated. During his work in IHEP (Protvino) Pavel Ermolov got acquainted with a youn German physicist Robert Klanner during the secont joint experiment CERN-Serpukhov (1970-1973). Later (during 1973-75) they continued contacts in FNAL (USA) within the frames of the experiment on the searching for charm production. Pavel Ermolov was a Head of one of the first neutrino experiments E-180 (FNAL, USA). It explained his permanent interest in deep non-eleastic processes. At MSU Physics Faculty Professor Ermolov gave series of lectures about lepton interactions which produced a basis for his book “Lepton interactions at high energies” (MSU Publishing house, 1st edition 1984, 2nd edition 1987).
In May 1992 operation of the first electron-proton collider HERA was started. Scientific program of the experiment was very wide and included detailed studies of lepton-quark interactions, quark and gluon structure of protons and virtual photon, mechanisms of production of heavy quarks, search for new elementary particles, verification of the Standard Model (SM) of electrically weak interactions and quantum chromodynamics, search for departures from the Model. By the beginning of data collection at ZEUS detector R. Klanner was the second person in the collaboration administration and was an ideologist and Chief of the development of the central calorimeter ZEUS from depleted uranium. This fact simplified contacts with DESY and conversations about the participation of DEHEP SINP in ZEUS experiment. Scientists of DEHEP could suggest their participation in the material input to ZEUS, in particular, development of hadron-electron separator HES. Due to this reason a number of SINP scientists (G.L. Bashidzhagyan, P.F. Ermolov, Yu.A. Golubkov, V.A. Kuz'min, E.N. Kuznetsov, A.A. Savin, A.G. Voronin, N.P. Zotov) were included as co-authors of the first article by ZEUS collaboration about measrements of total cross-section of interaction of photon and proton published in 1992. In 1993 SINP MSU became an official participant of ZEUS collaboration. List of participants from DEHEP became significantly wider. So DEHEP scientists got a principally new possibility for direct participation in the experiments in other conditions and with other organization of the scientific process without hard hierarchy.
LEEPP scientists took part in technical support of the experiment and in the physical analysis of experimental data. Technical support included duties on ZEUS facility during data coolection periods, improvement of simulation programs by Monte-Carlo method (Amadeus project), improvement and development of autamated system for data collection and primary procession. LEEPP scientists are co-authors of over 220 articles of ZEUS collaboration with description of scientific results. The following results can be noted among the basic:
determination of the upper limit for the cross-section of deeply non-eleastic processes initiated by instantons;
the sea of strange quarks in the proton was observed directly and φ-mesons spectrum was measured;
strange barion with mass of 1520 MeV in the channel of (Ks + p) decay interpreted as five-quark state θ+ was reconstructed;
kinematic selection criteria which suppress combinator background during resonances reconstruction were offered;
the search of five-quark barion which includes charmed quark was completed;
strange particles spectra were studied;
mechanisms of hadrons and leptons were studied theoretically.

Collider Tevatron (FermiLab, USA) was the most powerful accelerator before LHC operation was started. Beginning from 1993 LEEPP scientists take part in the experiment D0 which take place on one of two collider's detectors. The studies began from the offer of SINP scientists to solve the problem of search for Higgs bozon in the channels of assocative production woth W and Z bozons. Importance of this problem became evident during the second start of collider's operation after detector's improvement and luminosity increasing. As a result of long-term analysis it was announced about the observation of Higgs bozon production on Tevatron collider simultaneously with discovery of Higgs bozon on LHC in 2012.

The main goal of SINP scientists in D0 collaboration was to study single production of top-quark during electroweak interactions. In 1995 a group on the studies of single top-quark production discovered that year in dual production of top and antitop-quarks during strong interactions was formed in collaboration with University of California Riverside. Cross-section of single production is approximately twice less than cross-section of dual production, but in contrast to dual production the background processes are significantly greater than the signal. Development of a number of signal optimisation methods were needed due to complication of this problem. In particular, new more accurate methods of signal processes simulation taking into account radiation corrections and integrating different orders of perturbation theory in a correct way were developed. Methods for artificial neural networks application were developed in order to separate signal events from background. Methods for simulation and analysis of demonstrations of possible departures from Standard Model predictions in the processes with single top-quark production were developed. Conducted studies provided an opportunity for the first experimental observations of electroweak production of top-quark in the data obtained by D0. In 2007 series of studies awarded First Class M.V. Lomonosov Prize by MSU.

Starting from 1998 the scientists of the Laboratory participate in CMS experiment at LHC collider in the European Center of Nuclear Research (CERN) in Geneva, Switzerland. Preliminary analysis of the opportunities of the experiment during the search for single production of top-quark was carried out, its results were presented in Technical Design Report of CMS experiment. Experience of the scientists of the Laboratory got during the studies at Tevatron collider provided a possibility to use developed analysis methods at new levels of energy and with the start of data collection in CMS experiment. Besides, the scientists of the Laboratory got in a number of problems attached to electroweak production of top-quark and to the search of possible departures from SM's predictions in this processes.