G. A. Bogdanova

Observation of a narrow baryon resonance decaying to pK S 0 in proton-nucleus interactions at 70 GeV/c with the SVD-2 setup

AbstractData from the SVD-2 experiment that were obtained at the IHEP accelerator in 70-GeV/c proton-nucleus interactions are analyzed with the aim of searches for an exotic Θ+ baryon that decays through the pKS0 channel. The reaction pN → pKS0 + X characterized by a bounded multiplicity of charged secondaries is used for this analysis. A resonance of mass M = 1526 ± 3(stat.) ± 3(syst.) MeV/c2 and width Γ < 24 MeV/c2 is observed in the invariant-mass spectrum of the pKS0 system at a statistical significance of 5.6σ. The mass and the width of this resonance correspond to the recently found positive-strangeness Θ+ baryon, which was predicted to be an exotic baryon consisting of five quarks (pentaquark),

A trigger of events with a high multiplicity of charged particles at the SVD-2 setup

uudd\bar s

Measurement of the production cross section for charmed baryons in proton–nucleus interactions at 70 GeV

. The total cross section for the production of a Θ+ baryon in pA interactions is estimated at a value within the range 30–120 μb for xF ≥ 0. An analysis of the A dependence of the cross section for Θ+-baryon production does not reveal a significant deviation from the A dependence for inelastic events (∼A0.7).

A Soft Photon Calorimeter for the SVD-2 Experiment

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.

A vertex microstrip detector of the SVD setup for experiments on the IHEP accelerator

The Thermalization project is currently under way on the extracted proton beam of the U-70 accelerator at the Institute for High Energy Physics. The main goal of this experiment is to study the collective behavior of secondary particles produced in a multiparticle pp interaction at beam energy E = 50–70 GeV. The region of high charged-particle multiplicities nch ≥ 10 is investigated. In this region, a significant portion of energy in the center-of-mass system is dissipated on production of secondary particles, which results in formation of a hadronic system. At the initial instant of evolution, the density of this system is high, which may be responsible for the collective behavior of the secondary particles. The investigations are performed at the SVD-2 wide-aperture magnetic spectrometer. A multichannel trigger scintillation hodoscope used to select rare events with a large number of charged particles exceeding the predetermined value is described. The main flow of low-multiplicity events is suppressed by the trigger system by a factor of ∼102.

Experimental estimation of the charm-production cross section in pp interactions at 70 GeV/c with the aid of the SVD setup

The design and the characteristics of a drift tracker for the SVD-2 setup at the U-70 accelerator of the Institute for High Energy Physics (Protvino, Russia) are described. The drift tracker has been developed to improve the quality of track reconstruction in high-multiplicity events. It is composed of 2304 drift tubes with a diameter of 6 mm and a sensitive region 500–900 mm long. The distance between a track and the anode wire is determined from the drift time. The coordinate resolution and the detection efficiency of the tubes have been determined from the data of the accelerator run in 2006.

Electronic equipment for readout and processing of data from the microstrip vertex detector of the SVD-2 setup

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 Λc+ baryons. After selecting a signal from the threebody decay of a Λc+ 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 Λc+ -baryon yields are tabulated along with data from other experiments and theoretical predictions.

Electronic Equipment for Reading and Recording Signals from the Microstrip Vertex Detector of the SVD-2 Setup

The design of the soft photon calorimeter for the SVD-2 experiment is described. The aperture of the calorimeter is 210 × 210 mm. The first results of its testing in the course of data acquisition in the E-190 experiment at the U-70 accelerator of the Institute for High Energy Physics are presented.