A. N. Aleev

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), n

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

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Searches for the pentaquark states Ξ(1860)0 and Ξ(1860)−− in neutron-carbon interactions via the EXCHARM experiment

n. 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).

Associated production of ϕ mesons and neutral kaons in the EXCHARM 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.

Correlation femtoscopy in neutron-carbon interactions at average neutron energy of 51-GeV

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.

Associated φΛ0 production in the EXCHARM experiment

The 5N neutral particle beamline at the U-70 accelerator (Institute for High Energy Physics), which has been designed to produce a high-intensity neutron beam with the highest possible energy, is described. The average neutron energy is ∼51 GeV, and the beam intensity is up to 107 neutrons per spill. For several years, this beam has been used to investigate charmed particles and narrow baryon resonances in neutron-nucleus interactions and search for exotic multiquark states with the aid of the EXCHARM spectrometer.

Neutral pion number fluctuations at high multiplicity in pp-interactions at 50 GeV

Results of searches for the pentaquark states Ξ(1860)0 and Ξ(1860)−− in neutron-carbon interactions at an average neutron energy of about 51 GeV via the EXCHARM experiment are presented. No such states are found in the Ξ−π+ and Ξ−π− effective-mass spectra examined in this study. Upper limits on the cross sections for Ξ(1860)0 and Ξ(1860)−− production are estimated.

New analysis on narrow baryon resonance decaying into pK0(s) in pA-interactions at 70-GeV/c with SVD-2 setup

The features of the associated production of ϕ mesons and neutral kaons are studied on the basis of data obtained at the EXCHARM spectrometer (Serpukhov accelerator) in neutron—carbon interactions at neutron-beam energies in the range 20–70 GeV. The cross section for the inclusive associated production of ϕ and K0/-K0 is obtained. The fraction of processes allowed by the Okubo-Zweig-Iizuka rule is estimated in the reactions of ϕ-meson inclusive production.