Higher baryon resonances in carbon-carbon collisions at 4.2 GeV/c per nucleon

The production of the N(1440), the so-called Roper, and N(1520) resonances in high-energy collisions of carbon nuclei with the carbon nucleus, using a 2 m propane bubble chamber, was investigated. Attention was paid to the two-pion decay mode of the higher baryon resonances. From the invariant masses of three-particle states the mass and width of the resonances were obtained. The ratio of the resonances decay to and states was estimated.Received: 1 July 2003, Revised: 29 September 2003, Published online: 20 April 2004PACS: 25.70.Ef Resonances - 14.20.Gk Baryon resonances with S = 0     

Interactions of12C ions with emulsion nuclei at momentum 4.2 GeV/c per nucleon and the cascading-evaporation model

Transport equations (master and Fokker-Planck equations) are derived in the Markov approximation. The main features of weak and strong coupling are presented. In the weak-coupling limit conservative and dissipative effects from the coupling are separated according to virtual and real transitions. For the strong-coupling limit the Markov approximation is justified only after the ad hoc restriction to on-shell transitions. The main reason for the occurrence of the strong-coupling limit is attributed to the specification of global many-particle quantities for the intrinsic degrees of freedom. It is concluded that the alternative treatment of single-particle quantities is advantageous.     

Formation of six-nucleon systems and nuclei in 16Op collisions at a momentum of 3.25 GeV/c per nucleon

The results obtained by studying the production of six-nucleon systems and nuclei that is accompanied by the yield of charged pions in ¹⁶Op collisions at a momentum of 3.25 GeV/c per nucleon are presented. It is shown that the correlation of the yield of mirror ³H (³He) nuclei with the production of π ⁺ (π ^?) mesons is due to the charge-exchange process involving an oxygen-nucleus proton (neutron) knocked out predominantly from an alpha-particle cluster.     

Projectile stopping in nucleus-nucleus and hadron-nucleus collisions at 4.2 and 10 GeV/c per nucleon

The collisions ofp,²H,⁴He and C with carbon and tantalum nuclei at 4.2 GeV/c per nucleon as well as the collisionsp-C andp-Ta at 10 GeV/c from 2-m propane bubble chamber have been studied. New results on nuclear stopping have been obtained from the examination of proton rapidity distributions and average rapidity of leading protons for collisions of various degree of centrality: our study points out that a proton projectile is fully stopped in the centralp-Ta collisions at 4.2 GeV/c but only partly stopped at 10 Gev/c. The proton multiplicity in the centralp-Ta collisions at 10 GeV/c can be described by the binomial distribution,P(n), which expresses the probability that the projectile meetsn protons among the nucleons being along the diameter of a target nucleus.     

Strange baryon signals of deconfinement in Pb−Pb collisions at 158 GeV/c per nucleon

The main results of the CERN WA97 heavy ion experiment are summarized. The evidence for the formation of a deconfined state of matter in Pb?Pb collisions at CERN SPS energies, provided by these results, is discussed. The ongoing experimental efforts, by the CERN NA57 experiment, to investigate the onset of deconfinement are briefly reviewed.     

Features of CC interactions at a momentum of 4.2 GeV/c per nucleon for various degrees of nuclear-collision centrality

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.     

Production of $ \Delta$(1232) -resonances on oxygen nuclei in 16O + p collisions at a momentum of 3.25 GeV/c per nucleon

The production of D⁺⁺ \Delta^{{++}}_{} and D⁰ \Delta^{0}_{} resonances on oxygen nuclei in ¹⁶O + p interactions at 3.25A GeV/c was investigated with 4p \pi acceptance. The masses and widths of the resonances were obtained from an analysis of the experimental and background invariant-mass distributions of pp^± \pi^{{\pm}}_{} pairs. The fractions of charged pions coming from D⁺⁺ \Delta^{{++}}_{} and D⁰ \Delta^{0}_{} decay were estimated. The momentum, kinetic energy, and emission angle distributions of D⁺⁺ \Delta^{{++}}_{} and D⁰ \Delta^{0}_{} resonances were reconstructed in the oxygen nucleus rest frame. The slope parameters, T₀ , of the reconstructed spectra of invariant cross-sections of D⁺⁺ \Delta^{{++}}_{} and D⁰ \Delta^{0}_{} resonances, produced on oxygen nuclei in ¹⁶O + p interactions at 3.25A GeV/c , were determined.     

Contribution of excited nuclei 12C* to the channel of three-alpha-particle production in 16Op collisions at a momentum of 3.25 GeV/c per nucleon

Physics of Atomic Nuclei - A phenomenological analysis of the channel involving the production of three alpha particles in collisions of relativistic oxygen nuclei with protons is performed for the...     

Contributions of excited 6Li and 7Li nuclei to the production of 4He+2H and 4He+3H systems in 16O p collisions at a momentum of 3.25 GeV/c per nucleon

New experimental data on the cross sections for the yield of excited ⁶Li* and ⁷Li* nuclei and on their contributions to the production of ⁴He + ²H and ⁴He+³H light dinuclear systems in ¹⁶O _p collisions at a momentumof 3.25 A GeV/c per nucleon are presented.     

Possible mechanisms of fragmentation of 16O nuclei with a momentum of 4.5 GeV/c per nucleon in track emulsions

The angular distributions of doubly charged fragments of ¹⁶O nuclei having a momentum of 4.5 GeV/c per nucleon and interacting with track-emulsion nuclei were studied. The experimental angular distributions of doubly charged fragments of a ¹⁶O nucleus are not described by the statistical model of the fragmentation of nuclei. The possible channels of fragmentation of ¹⁶O nuclei may include ¹⁶O → 2⁸Be → 4α, ¹⁶O → ⁸Be +⁸ Be* → 4α, ¹⁶O → 2⁸Be* → 4α, ¹⁶O → α+¹²C, ¹⁶O → α +¹²C* → α + 3α, ¹⁶O → α +¹²C* → α + pα ⁷Li, ¹⁶O → α +¹²C* → α + 2⁶Li, ¹⁶O → α +¹²C* → α + pt2α, ¹⁶O → Li + B, and ¹⁶O → Li* + B*.     

Production of delta isobars on tantalum nuclei in CTa collisions at a projectile momentum of 4.2 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

A procedure that relies on analyzing the angle between the momenta of the proton and the pion originating from CTa interaction at a projectile momentum of 4.2 GeV/c per nucleon was used to investigate for the first time the production of Δ⁰ and Δ⁺⁺ resonances in such interactions and to determine their parameters. The criterion of stability in the parameter a characterizing the background contribution was presented for the first time and was used to reconstruct the mass distributions of Δ⁰ and Δ⁺⁺ resonances. The contributions of Δ⁰- and Δ⁺⁺-resonance decays to the production of charged pions were estimated. The results of this study are compared with similar data obtained by using the analogous procedure for Δ⁰ and Δ⁺⁺ resonances produced on carbon nuclei in CC and ⁴HeC collisions at a projectile momentum of 4.2 GeV/c per nucleon and in π ⁻¹²C interactions at a projectile momentum of 40 GeV/c.     

Suppression of charmonium production in PbPb collisions at 158 GeV/c per nucleon and quark-gluon deconfinement

An anomalous suppression of the charmonium yield in central collisions was observed in studying charmonium production in collisions of Pb nuclei accelerated to a momentum of 158 GeV/c per nucleon with Pb target nuclei. It is shown that, in peripheral collisions, the ratio of the cross section for J/ψ production to the cross section for the Drell-Yan process decreases exponentially (as in the case of collisions of lighter nuclei) owing to the ordinary absorption of J/gy in nuclear matter. The observed threshold effect of the anomalous suppression of charmonium production agrees well with the predictions based on the assumption of Debye color screening in the formation of quark-gluon plasma.     

Fission and fragmentation of 208Pb nuclei in collisions with gold nuclei at an energy of 158 GeV per nucleon

The fission and fragmentation of ultrarelativistic ²⁰⁸Pb nuclei in collisionswith gold nuclei were studied by using a beam from the SPS accelerator at CERN at an energy of 158 GeV per nucleon. The detectors of the target area of the NA45/CERES spectrometer were used in respective measurements. The value obtained for the fission cross section is 301 ± 44 mb, where about 77% of events stem from the electromagnetic interaction of colliding nuclei, while the remaining part is the contribution of peripheral nuclear interactions. The spallation of lead nuclei that involves the formation of heavy fragments occurs only in collisions where the impact parameter satisfies the condition b > 10 fm. A complete disintegration of lead nuclei to intermediate-mass fragments and light particles is observed in some peripheral collisions.     

Small-angle correlations of identical particles in carbon-carbon interactions atP=4.2 GeV/c per nucleon

Two-particle small-angle correlations between negative pions and between protons in carbon-carbon collisions atP=4.2 GeV/c per nucleon have been studied, both for an unbiased sample and for “central” events. A comparison of experimental π^? π^? andpp correlation functions with theoretical predictions has been made. A possible evidence for the existence of two fireballs in C+C interactions atP=4.2 GeV/c per nucleon is presented.     

Event-by-event fluctuations of average transverse momentum in central Pb+Pb collisions at 158 GeV per nucleon

We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb+Pb collisions at the CERN SPS. This measurement provides previously unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement.     

Strange particle production in nuclear collisions at 200 GeV per nucleon

Multiplicities and spectra of strange particles ( andK ^– produced in central³²S+S,³²S+Ag and³²S+Au collisions at 200 GeV per nucleon are presented and compared with data on strange particle production in protonnucleus and nucleon-nucleon interactions. It is shown that strangeness production in³²S+Ag collisions is enhanced by a factor of two, similar to that found previously in central³²S+S collisions.