(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.

The results of an analysis of data from the SERP-Е-184 experiment devoted to studying mechanisms of the production of charmed particles in proton–nucleus interactions at 70 GeV and their decays are presented. The data in question were obtained upon irradiating the SVD-2 active target consisting of carbon, silicon, and lead plates with a beam of 70-GeV protons. A detailed simulation on the basis of the FRITIOF7.02 and GEANT3.21 code packages made it possible to optimize event-selection criteria and to calculate the detection efficiency for Λ c + baryons. After selecting a signal from the threebody decay of a Λ c + baryon, the inclusive cross section for its production at near-threshold energies, its lifetime, and the parameter of the A dependence of the cross section were found. The Λ c + -baryon yields are tabulated along with data from other experiments and theoretical predictions.

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.

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.

Charmed-particle production in pp interactions at 70 GeV/c was studied with the SVD setup at the IHEP accelerator (Protvino). The experimental procedure used and the data-selection methods are described. Data obtained by using a quickly cycling bubble chamber and a magnetic spectrometer are analyzed. The number of inelastic-interaction events recorded in the chamber is 109000, with the charge multiplicity being nch/4. The corresponding statistics are 4.96 event/µb. Part of the events were recorded in the magnetic spectrometer. Three three-prong decays of charged particles near the primary vertex are found on the films, two of these being recorded with the spectrometer. All three are interpreted as D− decays. Two neutral decays observed simultaneously in the chamber and in the spectrometer are interpreted as \(\bar D^0 \) decays. The total cross section for \(c\bar c\) production in the Feynman variable region −1<xF<+1 is estimated at \(\sigma (c\bar c) = 1.6_{ - 0.7}^{ + 1.1} (stat.) \pm 0.3(syst.)\mu b\). The cross-section values and the mean values 〈|xF|〉 and 〈p⊥〉 for D mesons are compared with other experimental results in the energy range 58–800 GeV. The data of this experiment are compatible with the cross-section estimates obtained in the beam-dump experiment at 70 GeV and with those predicted by perturbative QCD.

A double-loop helium refrigeration system is developed to stabilize the operating conditions of a liquid-hydrogen rapid-cycling bubble chamber. The system makes it possible to reduce the amount of liquid hydrogen used to a minimum and thus to localize the dangerously explosive zone within the boundaries of the vacuum housing. Under operating conditions, the system maintains temperature and pressure to an accuracy of +/-0.005 K and +/-0.01 atm, respectively, Consumption of liquid helium is within 60 1/day.

A precision liquid hydrogen bubble chamber with rapid cycling capability and a photographed volume of 150 × 70 × 50 mm3 has been constructed to study short-living elementary particles. Its refrigeration system is operated with liquid helium. The chamber body, manufactured from the polycarbonate Lexan®, is almost free of vibrations due to the innovative expansion system with two pistons operating in opposite directions. The chamber operates with 5 ms cycle time and a rate up to 30 s−1. The chamber has already been cycled 6.7 million times and about 0.3 million pictures have been taken. At the hydrogen temperature of 29.8 K a track density of 150 bubbles/cm has been achieved with bubble diameters of 25 μm.

Photoemission spectra of the YBa2Cu3O7−x compound have been measured. It is shown that the shape of the spectra changes appreciably depending on the time elapsed after cleaning of the sample surface and on the photon energy. The spectra were measured immediately after cleaning and have a considerable density of states at the Fermi level and resemble the density of states obtained from single-electron band calculations. A resonance character of the photoemission is observed at 12 eV.