Search

Multiparticle azimuthal correlations of π − mesons have been studied in dC, HeC, CC, CNe, MgMg, (d, He)Ta, CCu, CTa, and OPb collisions at momentum of 4.2, 4.5 GeV/c per nucleon within the standard transverse momentum analysis method of P. Danielewicz and G. Odyniec. The data were obtained by SKM-200-GIBS and Propane Bubble Chamber Collaborations of JINR. The axis has been selected in the phase space and with respect to this axis π − meson correlations were observed. The values of the coefficient of the correlations linearly depend on the mass numbers of projectile (A P ) and target (A T ) nuclei. The Quark-Gluon String Model satisfactorily describes the experimental results.

Features of anisotropic collective flow and spectral temperatures have been determined for Λ hyperons emitted from C + C collisions, at incident momentum of 4.2 A GeV / c , measured using the Propane Bubble Chamber of JINR at Dubna. Moreover, characteristics of protons and of negative pions, emitted from those collisions, have been determined and provided for comparison. The directed and elliptic flows of Λ s both agree in sign with the corresponding flows of protons. Parameters of the directed and elliptic flows for Λ s agree further, within errors, with the corresponding parameters for the co-produced protons. This contrasts an earlier finding by the E895 Collaboration of the directed flow being significantly weaker for Λ s than protons, in the much heavier Au + Au system, at comparable incident momentum. Particle spectral temperatures in the C + C collisions have been determined focusing independently on either center-of-mass energy, transverse energy or transverse momentum distributions. For either protons or negative pions, the temperatures were found to be approximately the same, no matter whether the emission of those particles was associated with Λ production or not. Results of the measurements have been compared to the results of simulations within the Quark–Gluon String Model.

Collective flow of protons and negative pions has been studied within the momentum region of $4.2 \div 4.5$ AGeV/c ($E =3.4 \div 3.7$ AGeV) for different projectile-target combinations involving carbon and, specifically, He-C, C-C, C-Ne, C-Cu and C-Ta. The data stem from the SKM-200-GIBS streamer chamber and from Propane Bubble Chamber systems utilized at JINR. The directed flow of protons grows dramatically in the carbon region when the counterpart nucleus grows in mass between He and Ta. The elliptic proton flow points out of the reaction plane and also strengthens as system mass increases. Within the reaction plane, the negative pions flow in the same direction as protons for the lighter of the investigated systems, He-C, C-C and C-Ne, and in the opposite direction for the heavier, C-Cu and C-Ta. The Quark-Gluon String Model reproduces observed changes in the flow with system mass.

Experiemntal data obtained by using the 2-m propane bubble chamber of the Joint Institute for Nuclear Research (JINR, Dubna) are used to study the effect collision centrality on the spectra of Λ hyperons and KS0 mesons produced in carbon-carbon interactions at 4.2 A GeV/c. The multiplicity of participant protons having momenta in excess of 300 MeV/c is taken to be a measure of collision centrality. The features of pions and protons accompanying strange-particle production are also presented. The experimental data in question are compared with the prediction of a modified version of the FRITIOF model. It is shown that strange particles are predominantly produced in central and semicentral collisions. The average kinematical features of KS0 mesons are found to be indepedent of collision centrality. At the same time, the average transverse momentum of Λ hyperons and the average value of their emission angle increase slowly with increasing degree of collision centrality. The anisotropy of the angular distributions of both Λ hypersons and KS/0 mesons in the c.m. frame of nucleon-nucleon collisions decreases with increasing collision centrality. The average transverse momentum of KS0 mesons is approximately 1.6 times higher than the average transverse momentum of π− mesons.

The inclusive spectra of pions produced in CC and CTa collisions at a momentum of 4.2 GeV/c per nucleon are analyzed in terms of light-front variables ξ and ζ. The phase space of the secondary pions is divided into two parts with very different angular and momentum distributions. In one of these parts, the thermal equilibrium assumption seems to be in good agreement with the data. Corresponding temperatures T are extracted, and their dependence on (A PAT)1/2 is studied: T decreases linearly with increasing (A PAT)1/2. The results are compared with the predictions of the quark-gluon string model (QGSM). The QGSM satisfactorily reproduces the experimental data.

Directed (in-plane) flows of protons, pions, and projectile light fragments (d, t, 3He, 4He) have been observed by investigating the dependence of the mean transverse momentum in the reaction plane 〈px〉 on the rapidity y in the c.m. system for CC collisions at a momentum of 4.2 GeV/c per nucleon. The comparison of our in-plane-flow results of protons with flow data for various projectile/target configurations was made using the scaled flow Fs = F/(AP1/3 + AT1/3). Fs demonstrates a common scaling behavior for flow values from different systems. From azimuthal distributions of protons and π− mesons, out-of-plane (squeeze-out) flow effects have been observed and the parameter a2 (the measure of the anisotropic emission strength) has been extracted. The quark-gluon string model reproduces the experimental results quite well.

The mean values of the momenta and emission angles of charged pions and protons in the laboratory frame are presented both for the total ensemble of interactions between 4.2-GeV/c protons and a carbon nucleus and for six groups of events characterized by different degrees of collision centrality. The distributions with respect to the total and the transverse momentum are presented for the particles being studied, along with the longitudinal-rapidity distributions. Our experimental data are compared with the predictions of the cascade-evaporation model and of two versions of the refined FRITIOF model. It is shown that, as the degree of collision centrality becomes higher, the mean momenta and rapidities of secondaries decrease, the transverse momenta remain virtually unchanged, and the mean angles of particle emission increase. This is consistent with the pattern of particle cascading in nuclei. However, the mean transverse momentum 〈p t 〉 of participant protons that was obtained on the basis of the cascade-evaporation model decreases with increasing degree of collision centrality, in contrast to what is observed in our experiment. A satisfactory description of experimental data is on the basis of the refined FRITIOF model taking into account Δ+ and Δ0 isobars. The stopping power of carbon nuclei for 4.2-GeV/c protons is also determined.

New experimental data obtained for the multiplicities of charged pions and protons from the interaction of 4.2-GeV/c protons with a carbon nucleus by using the 2-m propane bubble chamber installed at the High Energy Laboratory (Joint Institute for Nuclear Research, Dubna) are presented versus the degree of collision centrality. The parameter Q defined for each individual event as the difference of the total multiplicities of positively and negatively charged particles without allowing for the multiplicity of evaporated protons whose momentum is less than 0.3 GeV/c is taken for a criterion of the degree of collision centrality. It is shown that, with increasing Q, the multiplicity of positively charged pions and the multiplicity of participant protons from the target nucleus grow considerably; concurrently, the multiplicity of negatively charged pions remains at nearly the same level, while the mean multiplicity of evaporated protons decreases sharply. Our experimental data are compared with the results of calculations based on the cascade-evaporation model and the modified FRITIOF model. Within the FRITIOF model, nonnucleon degrees of freedom in nuclei (Δ+, Δ0 isobars) are taken into account for the first time, and the resulting description of the features of secondary particles appears to be by and large satisfactory.

The multiplicity, rapidity, and transverse-momentum distributions of secondaries (negative pions and protons) from CC interactions characterized by various numbers of participant protons are presented. It is shown that, in contrast to the mean transverse momenta of protons, the mean transverse momenta of pions depend only slightly on the degree of collision centrality. The shape of the rapidity distributions of negative pions is also weakly dependent on the degree of collision centrality. With decreasing impact parameter, the product protons are found to concentrate in the central rapidity region. The data in question are analyzed within the modified version of the FRITIOF model. It is shown that, as soon as elastic nucleon rescatterings are taken into account, the model describes satisfactorily the experimental features of negative pions and fast protons. The spectra of slow protons are described only qualitatively because of limitations of the evaporation model used here to treat the deexcitation of residual nuclei.

The mean multiplicities of π− mesons and protons originating from pC, dC, αC, and CC interactions at a momentum of p=4.2 GeV/c per projectile nucleon and the distributions of these particles in kinematical variables are presented. These experimental distributions are compared with the corresponding predictions obtained on the basis of the FRITIOF model. It is shown that the FRITIOF version used in the present analysis describes satisfactorily our experimental data.

Target and centrality dependence of pion and proton distributions is studied in C+C and C+Ta collisions at 4.2 GeV/c per nucleon using the 2-m propane bubble chamber. The experimental data are compared with the predictions of the Monte Carlo quark-gluon string model (QGSM). The pion and proton transverse momentum spectra at midrapidity are well described by the two-component thermal model. The shape of the proton rapidity distribution strongly depends on the collision centrality and reflects the stopping power of colliding nuclei. The pion rapidity distribution is Gaussian in shape regardless of the target mass number and collision centrality. The QGSM completely reproduces main features of pion and proton rapidity spectra as well as pion transverse momentum spectra. The model does not fully reproduce the features of the proton transverse momentum spectra.

Collective flows of protons and negative pions have been studied in ${}^{2}$H $+$ C, Ta and He $+$ C, Ta collisions at an energy of 3.4 GeV/nucleon. The data have been obtained by the 2-m Propane Bubble Chamber (PBC-500) at JINR. It is found that the directed flow of protons and \ensuremath{\pi}${}^{\ensuremath{-}}$ mesons characterized by $d\ensuremath{\langle}{P}_{x}\ensuremath{\rangle}/d(y)$ increases with increase of the mass numbers of colliding nucleus pairs; the elliptic proton flow points out of the reaction plane and also strengthens as the system mass increases; the negative pion directed flow is in the same reaction plane as the proton flow for the lighter (${}^{2}$H $+$ C, He $+$ C) systems and in the opposite direction for the heavier (${}^{2}$H $+$ Ta, He $+$ Ta) systems. In ${}^{2}$H $+$ C, He $+$ C, C $+$ C, C $+$ Ne, ${}^{2}$H $+$ Ta, He $+$ Ta, C $+$ Cu, and C $+$ Ta collisions, the linear dependence of directed and elliptic flow parameters from mass numbers of projectile and target nuclei, (${A}_{P}$\ifmmode\cdot\else\textperiodcentered\fi{}${A}_{T}$)${}^{1/2}$, is similar for protons while for \ensuremath{\pi}${}^{\ensuremath{-}}$mesons the dependence of directed flow parameters is stronger. The ultrarelativistic quantum molecular dynamical model (URQMD) enlarged by the statistical multifragmentation model (SMM) satisfactorily describes the obtained experimental results for all pairs of nuclei. The data for such asymmetric nuclear collisions are obtained, to the best of our knowledge, for the first time.

The slopes of the noninvariant center-of-mass energy spectrum of negative pions in inelastic collisions of {ital d}, {alpha}, C nuclei with C and Ta targets at 4.2{ital A} GeV/{ital c} are studied. The temperatures of the negative pion are obtained using the Boltzmann distribution. The two-temperature shape of c.m. energy spectra is observed. The values of temperature do not depend significantly both on collision centrality'' and on atomic weight of the projectile nuclei. The experimental results are compared with the quark-gluon string model. The influence of resonances and directly produced pions on temperature values is studied.

Two-particle azimuthal correlations are studied in 4.2 GeV/{ital c} per nucleon {ital d}C, {alpha}C, and CC collisions with a propane bubble chamber at JINR Dubna Synchrophasotron. It is found that the azimuthal correlations are different for different pairs of secondary particles, and that they also depend on the mass of the projectiles and the collision centrality. The majority of the observed characteristics can be accounted for by the kinematic correlations calculated from the model of independent nucleon-nucleon collisions. The only exception is the effect of close pairing of like particles considered to be due to the identical particle effect for pion pairs and to short-range strong interactions for proton pairs.

Average multiplicity of protons fromp, d, α andC interactions with carbon at 4.2 GeV/c/ N is shown to increase with the mass number of incident nucleus. ThisA dependence is stronger for fast protons than for the slow ones. Angular and momentum distributions are described by the Dubna Cascade Model. Some discrepancy is observed in the high momentum part of the distributions.

Correlations between secondary protons with small relative momenta have been studied in interactions of various light nuclei with the carbon target at 4.2 GeV/c per incident nucleon with the aim to determine the radius of the proton emission region. This radius is found to decrease with increasing momentum and transverse momentum of the proton pair, but it does not show any dependence on the mass of the projectile nucleus.

Two-particle rapidity correlations are studied in {ital d}C, {alpha}C and CC interactions at 4.2 GeV/{ital c} per nucleon using 2 m propane bubble chamber. The influence of collision centrality on the short-range correlation strength is also analyzed. Comparison with the Dubna intranuclear cascade model indicates that the independent nucleon-nucleon collisions may account for the observed correlations.

The influence of collision centrality upon mean kinematic characteristics and spectra of participant protons d+C, ..cap alpha..+C, and C+C interactions at 4.2 GeV/c per nucleon is analyzed. The net charge Q of secondary particles is used as a measure of collision centrality. An increase in of participant protons with increasing Q is observed for all types of interactions analyzed. The net charge is also seen to affect the form of the rapidity spectra of participant protons in C-C interactions. The intranuclear cascade model cannot explain the dependence of these proton characteristics upon Q.