Topological cross sections in proton-proton interactions at 50 GeV

Project Thermalization (Experiment SERP-E-190 at IHEP) is aimed to study the pp interactions at 50 GeV with large number of secondary particles. In this report the experimentally measured topological cross sections have been presented taking into account the detector response and procession effciency. These data are in good agreement with gluon dominance model. The comparison with other models is also made and shows no essential discrepancies.     

Fluctuations of the number of neutral pions at high multiplicity in pp interactions at 50 GeV

Results obtained by measuring fluctuations of the number of neutral pions in the SERP-E-190 Experiment (Thermalization Project) upon irradiating a liquid-hydrogen target of the SVD-2 setup with a beam of 50-GeV protons are presented. A simulation of the detection of photons from the decay of neutral pions with the aid of an electromagnetic calorimeter revealed a linear relation between the number of detected photons and the mean number of neutral pions in an event. After the introduction of corrections for the loss of charged tracks because of a limited acceptance of the setup, trigger operation, and the efficiency of the data-treatment system, distributions of the number of neutral pions, N ₀, were obtained for each value of the total number of particles in an event, N _tot = N _ch + N ₀. The fluctuation parameter ?? = D/??N ₀?? was measured. In the region N _tot > 22, fluctuations of the number of neutral pions increase, which, within statistical models (GCE, CE, MCE), indicates that the system involving a large number of pions approaches the pion-condensate state. This effect was observed for the first time.     

Measurement of the $$\boldsymbol{\Sigma^{0}/\Lambda^{0}}$$ Yield Ratio in $${pA}$$ Interactions at 70 GeV

Physics of Atomic Nuclei - The active target with C, Si and Pb plates was irradiated in 70-GeV proton beam at U-70 accelerator. The signal (270 events) from $$\Sigma^{0}\to\Lambda^{0}+\gamma$$...     

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

High-energy interactions in the region of extreme multiplicities

Physics of Atomic Nuclei - Hadron and nuclear interactions at high energies in the region of extreme multiplicities (much higher than mean multiplicities) are reviewed. Collective phenomena such as...     

Neutral kaon production in K+p interactions at 32 GeV/c

The production of neutral kaons in the reaction K⁺p → Kⁿ + X is studied at the incident momentum of 32 GeV/c. Inclusive cross sections and single-particle distributions are presented and compared with the data at lower energies. The total inclusive cross section amounts to 7.9 ± 0.3 mb at 32 GeV/c and is significantly higher than at lower energies due to the rapid rise of multikaon production. The fraction of Kⁿ's coming from the decay of the K¹ resonances stays roughly constant with energy between 8.2 and 32 GeV/c. In the central and beam fragmentation regions the single-particle distributions reveal no energy dependence between the 16 and 32 GeV/c data in contrast with the behaviour at lower energies, while in the proton fragmentation region the data are compatible with the trend observed at lower energies and with theoretical expectations.     

Associated average charged particle multiplicities in K+p interactions at 32 GeV/c

The average charged particle multiplicities, 〈n_R(M_X²)〉, in the reactions K⁺p → π^?X and K⁺p → K⁰X at 32 GeV/c are studied as functions of the mass squared M_X² of the “associated” system X. A comparison with the corresponding results obtained at lower incident momenta is presented.     

Properties of neutral charmed mesons in <Emphasis Type="Italic">pA</Emphasis> interactions at 70 GeV

The results of data handling for the E-184 experiment involving the irradiation of the active target, consisting of carbon, silicon, and lead plates by a 70-GeV proton beam are presented. When the two-prong neutral charmed meson decay signal was selected and the cross section for charm production at a near-threshold energy was estimated (σ(c $ \bar c $ \bar c ) = 7.1 ± 2.4(stat.) ± 1.4(syst.) μb/nucleon), some properties of D ⁰ and $ \bar D^0 $ \bar D^0 were investigated. These include the atomic-weight dependence of the cross section on the target mass number (its A dependence); the differential cross sections dσ/dp _t ² and dσ/dx _F; and the dependence of the parameter α on x _F, p _t ², and p _lab. The experimental results are compared with the predictions of the FRITIOF7.02 program.     

Detection of charged charmed D ± mesons in proton-nucleus interactions at 70 GeV with the SVD-2 setup

The results of processing the data of the SERP-E-184 experiment that studied mechanisms of the production of charmed particles in proton-nucleus interactions at 70 GeV and their decays are presented. The data were obtained in irradiating the SVD-2 active target consisting of carbon, silicon, and lead plates with a 70-GeV proton beam. A detailed simulation based on the FRITIOF7.02 and GEANT3.21 packages made it possible to optimize event-selection criteria and to calculate the detection efficiencies for D ^± mesons. After the selection of a signal from the three-body decay of charged charmed D ^± mesons, the inclusive cross sections for their production at threshold energies were measured along with respective lifetimes and parameters of the A dependence of the cross sections. The yields of D mesons and their ratios are compiled in a table along with data fromother experiments and the respective theoretical predictions.