(SVD-2 Collaboration) A. G. Afonin, E. N. Ardashev, V. F. Golovkin, S. N. Golovnya, S. A. Gorokhov, A. A. Kiryakov, A. G. Kholodenko, V. V. Konstantinov, L. L. Kurchaninov, I. S. Lobanov, E. V. Lobanova, G. A. Mitrofanov, V. S. Petrov, A. V. Pleskach, M. K. Polkovnikov, V. N. Riadovikov*, V. N. Ronzhin, V. A. Senko,N. A. Shalanda, M. M. Soldatov, Yu. P. Tsyupa, A. P. Vorobiev, V. I. Yakimchuk, and V. N. Zapolskii∗ IHEP, Protvino, Moscow region, Russia.

(EHS/NA22 Collaboration) 1 Institute of Physics, AM-375036 Yerevan, Armenia 2 Institute of Particle Physics, Hua-Zhong Normal University, Wuhan 430070, China 3 Department of Physics, University of Antwerp, B-2610 Wilrijk, Belgium 4 Centro Brasileiro de Pesquisas Fisicas, BR-22290 Rio de Janeiro, Brazil 5 Radboud University Nijmegen/NIKHEF, NL-6525 ED Nijmegen, The Netherlands 6 Institute for High Energy Physics of Tbilisi State University, GE-380086 Tbilisi, Georgia; now at Northwestern Univ., Evanston, U.S.A. 7 Scobeltsyn Institute of Nuclear Physics, Lomonosow Moscow State University, RU-119899 Moscow, Russia Now at DESY, Hamburg, Germany Boost invariance and multiplicity dependence of the charge balance function are studied in πp and Kp collisions at 250 GeV/c incident beam momentum. Charge balance, as well as charge fluctuations, are found to be boost invariant over the whole rapidity region, but both depend on the size of the rapidity window. It is also found that the balance function becomes narrower with increasing multiplicity, consistent with the narrowing of the balance function when centrality and/or system size increase, as observed in current relativistic heavy ion experiments.

Results on the multiplicity structure of diffractively excited meson and proton systems in n + / K +p in­ teractions at 250GeV/c are presented for diffractive masses up to about 9 GeV. The energy dependence of the average charge multiplicity and the shape of the multi­ plicity distribution in terms of KNO-scaling and negative binomial distribution are investigated. The diffractive systems are compared to e + e ~ , Ih and non-diffractive hh final states as suggested by modern approaches of the Pomeron-hadron collision. Systematic differences are found between diffractive meson and proton systems but also between diffraction and the reactions compared to.

The NA22 data on 7r" 7r” correlations are ana­ lyzed in terms of a number of twoand three-dimensional parametrizations (Gaussian space-time, Goldhaber, Bowler string-like, Bertsch hydrodynamical, Kopylov-Podgoretskii, etc.). Contrary to the results obtained for e+e” and pp col­ lisions, the Goldhaber parametrization, as well as string-like models, fail in describing the hadron-hadron data. Better fits are obtained in the framework of surface-emitting fireball­ like models, both when including and excluding hydrody­ namical expansion of nuclear matter. Our results indicate that pion radiation occurs at earlier stages of matter evolu­ tion than in nuclear collisions.

. The results of the SERP-E-184 experiment at the U-70 accelerator (IHEP, Protvino) are presented. Interactions of the 70GeV proton beam with carbon, silicon and lead targets were studied to detect decays of charmed D^0 , D̅^0 , D^+ , D^- mesons and Λ_c^+ baryon near their production threshold. Measurements of lifetimes and masses have shown a good agreement with PDG data. The inclusive cross-sections of charm production and their A -dependences have been obtained. The yields of these particles are compared with the theoretical predictions and the data of other experiments. The measured cross-section of the total open charm production ( σ_ tot(cc̅) = 7.1 ± 2.3( stat) ± 1.4( syst) μb/nucleon) at the collision c.m. energy √ s = 11.8 GeV is well above the QCD model predictions. The contributions of different kinds of charmed particles to the total cross-section of the open charm production in proton-nucleus interactions vary with energy.

The correlation of negative particles at small momentum difference and its dependence on multiplicity and on kinematical cuts is studied in n +/?-interactions at 250 GeV/c. In terms of the Kopylov-Podgoretskir parametrization, an average radius of the pion emitting region of rK — 1.59 ± 0.14 fm and a life-time (or emission depth) t = 0.83 ± 0.25 fm are found. The Lorentz invariant parametrization of Goldhaber gives rG= 0.85 ± 0.04 fm. As­ suming two different sources of pions, their radii are es­ timated as /■, = 1.75 ± 0.25 fm and r 2 = 0.60 ± 0.08 fm. An angular and multiplicity dependence of the space-time size of the source is observed. The source is elongated along the collision axis and has larger size rK at higher multiplicities. The radius rK decreases with increasing pion pair momentum. The size of the emitting region appears to be larger for low rapidity pions than for pions from the fragmentation region. No evidence is found for a unique reference frame, where the pion source is mo­ tionless for each n +p collision, i.e. where the space-time size of the source is definitely smaller than in any other frame.

Cross-sections are obtained for coherent interac­ tions of 7r+ and K +-mesons with A1 and Au nuclei at 250 GeV/c, leading to three, five and seven charged mesons. The total coherent cross-section is (4.3 ± 0.5)% of the inelastic cross-section for each of the four meson-nucleus interac­ tions. In 85% of the coherent events, the charged meson pro­ duction is accompanied by neutral mesons. Effective mass distributions are presented for coherently produced particles, including charged mesons and photons, carrying total mea­ sured energy of more than 85% of the initial energy. Charged particle and 7 spectra are analysed. No charge asymmetry is observed within the coherently produced cluster.

Cross-sections are obtained for coherent interac­ tions of 7r+ and K +-mesons with A1 and Au nuclei at 250 GeV/c, leading to three, five and seven charged mesons. The total coherent cross-section is (4.3 ± 0.5)% of the inelastic cross-section for each of the four meson-nucleus interac­ tions. In 85% of the coherent events, the charged meson pro­ duction is accompanied by neutral mesons. Effective mass distributions are presented for coherently produced particles, including charged mesons and photons, carrying total mea­ sured energy of more than 85% of the initial energy. Charged particle and 7 spectra are analysed. No charge asymmetry is observed within the coherently produced cluster.

The results of the SERP-E-184 experiment at the U-70 accelerator (IHEP, Protvino) are presented. Interactions of the 70GeV proton beam with carbon, silicon and lead targets were studied to detect decays of charmed \(D^{0}\), \(\bar{D}^{0}\), \(D^{+}\), \(D^{-}\) mesons and \(\Lambda_{c}^{+}\) baryon near their production threshold. Measurements of lifetimes and masses have shown a good agreement with PDG data. The inclusive cross-sections of charm production and their A-dependences have been obtained. The yields of these particles are compared with the theoretical predictions and the data of other experiments. The measured cross-section of the total open charm production ( \(\sigma_{\rm tot}(c\bar{c}) = 7.1 \pm 2.3({\rm stat}) \pm 1.4({\rm syst})\) μb/nucleon) at the collision c.m. energy \(\surd s = 11.8\) GeV is well above the QCD model predictions. The contributions of different kinds of charmed particles to the total cross-section of the open charm production in proton-nucleus interactions vary with energy.

The stages of development and the current status of the versatile “Spectrometer with a Vertex Detector” setup designed for physics experiments at the U-70 accelerator of the Institute for High Energy Physics (Protvino) is described. The main detectors of the setup are the vertex detector based on silicon microstrip detectors, the wide-aperture magnetic spectrometer based on multiwire proportional chambers, and the lead-glass hodoscope γ detector. In the setup, there is a fast two-level trigger system for selecting required particle interactions. The key characteristics of the setup systems are presented, and the physical results obtained on it are briefly listed.

The results of analysis SERP-E-184 experiment data, obtained with 70 GeV proton beam irradiation of active target with carbon, silicon and lead plates are presented. For 3-prongs charged charmed mesons decays, event selection criteria were developed and detection efficiency was calculated with detailed simulation using FRITIOF7.02 and GEANT3.21 programs. Signals of decays were found and charm production inclusive cross sections estimated at near threshold energy. The lifetimes and A-dependence of cross section were measured. Yields of D mesons and their ratios in comparison with data of other experiments and theoretical predictions are presented.

Описаны этапы развития и современное состояние многоцелевой установки “Спектрометр с вершинным детектором”, созданной для проведения физических экспериментов на ускорителе У-70 Института физики высоких энергий (Протвино). Основными детекторами установки являются: вершинный детектор на основе кремниевых микростриповых детекторов, широкоапертурный магнитный спектрометр на основе пропорциональных камер, годоскопический детектор -квантов, собранный из свинцовых стекол. Для отбора нужных взаимодействий частиц в установке имеется быстродействующая двухуровневая система запуска. Приведены основные характеристики созданных систем установки, кратко перечислены полученные физические результаты.

The results of data handling for E-184 experiment obtained with 70 GeV proton beam irradiation of active target with carbon, silicon and lead plates are presented. Two-prongs neutral charmed D0 and \v{D}0 -mesons decays were selected. Signal / background ratio was (51+/-17) / (38+/-13). Registration efficiency for mesons was defined and evaluation for charm production cross section at threshold energy is presented: sigma(c\^c) = 7.1 +/- 2.4(stat.) +/- 1.4(syst.) (\mu/nucleon).

A multi-dimensional analysis of two-particle correlations in + p-interactions at 250 GeV/c shows interesting structure. Particularly strong positive short-range ra-pidity and azimuthal correlations are observed for low-p T like-sign pairs. This observation is not reproduced by models used for comparison (FRITIOF, DPM, quark gluon (multi) string model). A possible explanation is Bose-Einstein interference not included in these models.

Описывается прецизионный вершинный микростриповый детектор, созданный для установки “Спектрометр с вершинным детектором”, на которой исследуются свойства адронов и короткоживущих нестабильных частиц на ускорителе ГНЦ “Институт физики высоких энергий”. Приведены структура, конструкция и технология изготовления основных компонентов детектора – микростриповых сенсоров и активной мишени; описываются также электроника съема и регистрации сигналов, система сбора данных и ее программное обеспечение. Точность определения положения вершин составляет 70–250 мкм вдоль оси пучка и 8–15 мкм – поперек оси при быстродействии 500–1000 событий/с.