Skobeltsyn Institute of Nuclear Physics
Lomonosov Moscow State University

Laboratory of hadronic interactions

Laboratory of hadronic interactions (LAI) was organized in 1967 as a Group of High-Mountains Research. In 1978 due to changes and extension of fields of research it was reorganized to the Laboratory of hadronic interactions as part of the Department of Experimental Physics of High Energy. Since its formation (1967) till 2011 the Laboratory was headed by Professor, DSc. Lyudmila Sarycheva. Beginning from 2011 up to now it's Head is DSc. Andrey Dem'yanov.

The Laboratory was organized in order to solve problems important at that time: composition and properties of cosmic rays at heights of the mountains, possible existance of the particles with fractional charge, characteristics of multiple partciles generation during hadronic interactions at high energy, dynamics of electronic-nuclear cascade development in the matter. The first Laboratory's experiment "PION" raised new problems. In order to solve them it was supposed to use opportunities provided by experiments on the accelerators.

Characteristics of the multiple generation of the particles during antiproton-proton and proton-proton collisions were studied y the experiment with a large lieuid-hydrogen chamber "MIRABEL" at U-70 accelerator of the Institute of High-Energy Physics (IHEP). Mechanism of production of J/ψ mesons was analysed by the experiment E672 on Fermilab Meson West Spectrometer. Propagation of intranuclear cascade which was observed during several experiments but exceeded the limits of simple cascade model required to carry out a new experiment pointed at the studies of this phenomenon ("Leading particles at U-10 accelerator of the Joint Institute of Nuclear Research (JINR)"). Different models ot strong interactions theory (Quantum Chromodynamics, QCD) inclding lattice calculations predict existance of coupled states of two gluons - a gluball, and so called hybrids - coupled states of a quark, antiquark and gluball. An experiment E852 "Search for mesons with unusual qunatum numbers" at AGS(BNL) accelerator was dealed with the search for these states.

Recently the scientists of the Laboratory carry out experimental and phenomenological studies of different aspects of QCD in new poorly studied modes of extremely high energy densities and temeperatures obtained during collistions of hadrons and nuclei of high energy. Processes of multiple particles production in these conditions contain important information about the properties of a new state of matter - quark-gluon plasma. It's production at sufficiently high temperatures and/or barion charge densities is predicted by QCD. Beginning of operation of Large Hadron Collider (LHD) in the European Center of Nuclear Researh (CERN) made this direction of research even more important. Experiments with heavy ions beams at LHC provide unique possibility for production of quark-gluon matter which existed during the early stages of the Universe development in the laboratory conditions. Studies of its properties is interesting both from the point of understanding of the nature of fundamental interactions and elementary particles origin, and from the point of verification of present-day theories of generation and evolution of the Universe.

Results of the studies of interactions between hadrons and cosmic rays (PION experiment) have shown that further development of this direction needs essentially different quality and bigger volume of experimental information obtained by accelerator experiemnts technique. So the Laboratory joined the collaboratio of the scientists analyzing the data of the hydrogen bubble chamber ("MIRABEL" experiment at U-70 accelerator of IHEP). Afterward the scientists of the Laboratory carried out an experiment "Leading particles" at U-10 accelerator of LHE JINR. Since the beginning of 1990s the Laboratory participates in the analysis of the experiment E672 (Fermilab) and then in the development and carrying out of the experiemtns E852 at AGS (BNL) accelerator within the frames of international collaboration E852 and in the analysis of ZEUS (DESY) experiment data. At the moment the scientists of the Laboratory take part in carrying out and analysis of the data of CMS and ALICE experiments at LHC.

The following steps were taken in order to achieve the objectives:
● "PION" experiment: manufacturing of an experimenatal plant at the high-mountain station Aragatz, measurements, development of specific methods for the obtained data analysis.
● "MIRABEL" experiment: participation in the production of measuring and computing complex of SINP mSY for full cycle of film information processing; development and customizing of application software; measurements carrying out and obtained data analysis.
● "Leading particles" experiment: development of experiment conception, manufacturing of a complex of equipment "Scintillation magnetic spectrometer" (SMS-MSU) at U-10 accelerator of LHE JINR, measuring and data analysis. In 2000-2002 the experiment was developed within the frames of a joint (with JUNR) project "SMS MSU - Sphere".
● E672 experiment: participation in the carrying out of measurements and data analysis concerning J/ψ mesons during pBe and π^–Be interactions at energy from 515 up to 800 GeV at Tevatron accelerator (Fermilab).
● E852 experiment: development and production of basic elements of experimental plant (prototypes of multi-channel γ-spectrometer and full-scale spectrometer for 3000 channels), carrying out of measurements, development of the methods of the obtained data analysis.
● ZEUS experiment: development of the methods for separation of diffraction of the events in electron-proton interactions at HERA accelerator and analysis of the obtained data.
● Experiments at LHC - the basic direction of the Laboratory activity in the recent years. The scientists of the Laboratory made a substantial input into technical and methodical maintenance of CMS experiment:
- development of mathematical model of magnetic filed of the CMS experimental plant and complex of equipment for measuring of magnetic flux density in the area of detectors and inside solenoid, carrying out of measurements and development of a full map of the plant's magnetic field;
- development, production and testing of the experimental equipment elements (a system for monitoring of neutron fluxes near HF calorimeter of CMS experimental plant), carrying out of measurements of neutron fields and radiancy of accelerator during the experiment;
- development of calibration program for hadron calorimeter CMS and program of reconstruction of dimuons in a tracking detector which allows to reconstruct dimuon resonances of small mass (Υ, J/ψ) under conditions of high loading of detector;
- development of correction algorythm for energy of streams by means of tracking detectors (JetPlusTrack), and of algorythm of search for streams and correction of their energy during collisions of heavy ions. These algorythms are used for analysis of physical processes, in particular, for studies of streams structure, Higgs bozon production during vector bozons fusion;
- development of the methods of separation of "hard" diffraction events, analysis of "hard" and "soft" diffraction channels with streams' production;
- development of the methods of model analysis of nuclear matter properties in the modes of extremely high energy densities and temperatures during relativistic collisions of heavy ions;
- development of new computer models of nucleus-nucleus interactions at high energy (Monte-Carlo generator of PYQUEN, HYDJET, HYDJET++ events) and simulation of different channels of particles production during heavy ions collisions at LHC;
- development of phenomenological model of production of so-called Centauro events - bunchs of quark matter with high bariochemical potential during heavy ions collisions and evaluation of their production cross-section at LHC energy;
- development of a fast method for specific analysis (wavelet-analysis) for the studies of structures at two-dimensional angular distribution of the particles during PbPb collisions at LHC energy;
- the Laboratory took active part in the development of a Russian calculating center for processing of data obtained by LHC collider and participate in maintenance of Тier2 center for the group on studies on heavy ions interaction (CMS HEAVY ION group);
- development of a Remote Operational Center – ROC MSU, which provides on-line access to the intranet of CMS experiment by the users outside CERN. The Center is used by the scientists of SINP MSU for remote control of the operation of detector systems of CMS equipment and the quality of the obtained information.

Within the frames of cooperation with JINR and University of Oslo the scientists of the Laboratory take part in the program of ALICE experiment directed on the studies in the field of heavy ions physics as part of groups specialized in the studies of impulse correlations of particles (ALICE-FEMTO group) and in the studies of anisotropic flow effects (ALICE-FLOW group):
- the scientists of the Laboratory made an essential input into the development of Monte-Carlo models UrQMD and QGSM and studies of hadron-hadron and nucleus-nucleus collisions within the energy range from several GeV up to 10 TeV;
- software for simulation and analysis of correlation functions during protons and nuclear collisions is developed. Developed computer models of heavy ions collisions (UKM, FASTMC) and adjusted existed computer models (QGSM) allow to describe experimental data successfully and are used for future experiments modelling.

The basic results of the Laboratory scientific activity:
● "PION" experiment: composition of the space hadrons flow (fractions of pions and protons) within the range of energy over 100 Gev at the altitude of mountains was evaluated basing on the measurements of ionisations in the multi-layer proportional counter and energy deposit inside calorimeter. There were registered "abnormal" hadrons among those falling unaccompanied on the instrument. They produce ionisation 1.51,5÷1,7 times higher than expected single-charged particles. A method of analysis of electron-nuclear cascades dynamics inside calorimeter is developed, nature of electromagnetic cascades and effect of inhibition of nuclear cascade absorption with a rise in energy which contradict simple cascade model are studied.
● "MIRABEL" experiment: mechanisms of multiple particles production during K^–-proton, proton and antiproton interactions at 32 GeV/s are studied. Inclusive cross-sections of charged hadrons production are found. Production of strange particles and antiproton-proton annihilation is studied. A method of statistical reconstruction of charged particles spectra is proposed. Characteristics of exclusive channels of particles production during antiproton-proton interactions are studied. Multi-particle correlation effects are analyzed depending on velocity by means of factorial moments method. In 1990 this study won Lomonosov Prize of MSU.
● "Leading particles" experiment: it is shown that protons fragmentation on the nuclei is carried out through coupled barion state (of isobar or diffrection cluster type), which is absorbed in the nuclear matter as conventional barion and decays to final hadrons outside of the nucleus. An effect of nuclei channeling (for carbon and oxygen) is discovered experimentally in a crinkled monocrystal of silicon. Characteristics of the effect are measured and the effect is used for particle beam extraction to the instrument. An experiment on the beam of polarized protons is carried out at U-10 accelerator for the first time. Spin effects in enalastic and non-elastic proton-nucleus scattering are studied and analyzing possibility of pA scattering on carbon and copper nuclei are measured in different channels of interaction depending on leading particle impulse.
● E672 experiment: channels with charmonium χ_c1 and χ_c2 production are separated in the region of 0.1< x _F < 0.8. Fractions of J/ψ from χ_c1 and χ_c2 decays, ratio of cross-sections of
χ_c1 and χ_c2 production and input of direct production of J/ψ are evauated. Differential distributions J/ψ, ψ(2S) by x _F, p²_T and by Godfrey-Jackson are measured. These results are included into International collected volume on elementary particles «Review of Particle Properties» (Particle Data Group).
● E852 experiment: the results of the experimental data analysis testify that observed states π₁(1400) and π₁(1600) with quantum numbers J ^PC = 1 ^{− +} are candidates to "exotic" mesons, forbidden by the Standard Model. Their parameters and decay characteristics are included into International collected volume «Review of Particle Properties».
● ZEUS experiment: diffraction processes at HERA collider are studied. Cross-sections of exclusive production of vector mesons within wide range of energy and virtuality of photons and cross-sections of inclusive diffraction processes are measured. The data is used for the development of diffraction parton distribution within the frames of QCD.
● Experiment at LHC:
1. Experimental results:
Cross-section of electroweak production of Z bozon accompanied by two tagging streams during рр interactions was measured for the first time during CMS experiment at proton energy of 7 TeV at statistics of 5 fb⁻¹. Obtained values for muon and electron channels of Z-bozon decay correspond with predictions of the Standard Model for NLO approzimation. Hadronic activity in the events µ+µ+jеt+jet and e+e+jet+jet is analyzed, this study is of particular importance for Higgs bozon separation.

Effects testifying about the production of hit quark-gluon matter during PbPb collisions at energy of √s_NN=2.76 Tev are studied: sequential suppression of output of different states of Y-mesons (1S, 2S, 3S) and asymmetry of transverse energy in the processes with production of jets pairs and production of photon+jet.
First experimental data on studies of correlations of identical kaons during pp and PbPb collisions and first experimental data on correltation of pions and kaons during pp collisions are obtained in ALICE experiment. Besides, first data on v₁-directed flow are obtained and analyzed.
2. Theoretical results:
Spatial and impulse distributions of quarks and gluons in hadrons and correlations between them are analyzed and it is shown that behaviour of cross-sections of double parton scattering deviates from factorization approzimation as consistent with QCD equations of evolution revealed during the research; the results are verified by data of experiment at LHC.
A process of hadronization of quark-gluon plasma within the frames of the first-order phase transition is studied: relaxation of primary state to chemical and thermal balance; problem of frees-out of the produced particles; production and evolution of "direct" v₁ and "elliptic" v₂ flows of charged pions, kaons,protons and antiprotons.
A state equation for hot and dense hadronic matter is obtained. It is found out that particles are emitted continuously during the period of system's expansion, and hadrons with big p_T are emitted during first 1-2 femtoseconds. Separation of "direct" flow into «normal» and «antiflow» is proposed and growing of «antiflow» for light nuclei is predicted.

Within the frames of the described projects the scientists of the Laboratory cooperate with colleagues from the Institute of High Energy Physics (MIRABEL), Joint Institute of Nuclear Research (Leading Particles), Fermilab, Indiana U (E672), BNL, Indiana U and a number of other Universities of the USA (Е852), DESY (ZEUS). At present time they work in collaborations with scientists from CERN (CMS), Oslo University (ALICE), NICA JINR (MPD).

Among the outstanding projects where the scientists of the Laboratory take part it is necessary to mark CMS and ALICE expriments at LHC collider and development of an experiment at NICA, NUCLOTRON-M: BM@N, MPD.

Plans of the Laboratory for the future includes: modernization of the equipment and continuation of the studies of the properties of hot super-dense matter basing on the analysis of mulciple production of hadrons during CMS and ALICE experiments at LHC; further improvement of computer models and theoretical approachs to the description of relativistic collisions of heavy ions taking into account data of the experiments at LHC, NICA and FAIR; development of theory of multi-parton interactions and experimental verifying of its predictions.

The scientists of the Laboratory are also involved into educational activity: the students of MSU Department of Physics do practical training and prepare their students and graduation thesis at the Laboratory; the scientists give lectures and seminars at MSU Department of Physics: "Physics of ultra-relativistic nuclei collisions" (V.Korotkikh) and "Select problems of QCD" (A.Snegirev) at the Chair of Atomic nucleus physics, 5th year; "Physics of elementary particles", 4th year and "Fundamental interactions and physics at colliders", 5th year, Chair of Space physics (I.Lokhtin). Basing on the research carried out in the Laboratory the scietists and post-graduates defended over 20 PhD and 4 DSc thesis.