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.     

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...     

Production of baryon resonances in collisions of 4He nuclei with carbon nuclei at a momentum of 4.2 GeV/c per nucleon

Under conditions of 4π geometry, Δ⁰-and Δ⁺⁺-resonance production in collisions of ⁴He nuclei with carbon nuclei at a momentum of 4.2 GeV/c per nucleon was investigated for the first time. The resonance masses and widths are estimated by analyzing the experimental and background invariant-mass distributions of (pπ ^±) pairs. Contributions to pion production from Δ-resonance decays, as well as from direct pion production, are determined. The results are compared with corresponding data obtained for CC collisions at the same primary momentum of 4.2 GeV/c per nucleon. By and large, the results obtained here comply with the existence of a collective mechanism of delta-isobar excitation in nuclei.     

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*.     

Inclusive production of charged pions in p+p collisions at 158 GeV/c beam momentum

New results on the production of charged pions in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. Pions are identified by energy loss measurement in a large TPC tracking system which covers a major fraction of the production phase space. Inclusive invariant cross sections are given on a grid of nearly 300 bins per charge over intervals from 0 to 2 GeV/c in transverse momentum and from 0 to 0.85 in Feynman x. The results are compared to existing data in overlapping energy ranges. Arrival of the final proofs: 8 December 2005     

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.     

Charged pion production in p+C collisions at 158 GeV/c beam momentum: Discussion

The new data on pion production in p+C interactions from the NA49 experiment at the CERN SPS are used for a detailed study of hadronization in the collision of protons with light nuclei. The comparison to the extensive set of data from p+p collisions obtained with the same detector allows for the separation and extraction of the projectile and target contributions to the pion yield both in longitudinal and in transverse momentum.     

Investigation of fragment production for fragment charge numbers between one and eight versus the degree of excitation of the fragmenting nucleus in 16Op collisions at a momentum of 3.25 GeV/c per nucleon

New experimental data on the mean-multiplicity distribution of fragments whose charge number ranges between one and eight and on the distribution of the mean kinetic energy of few-nucleon fragments (A = 1–3) are presented versus the 4-momentum transfer from the target proton to the oxygen nucleus in ¹⁶Op collisions at a momentum of 3.25 GeV/c per nucleon. These data are systematically compared with the predictions of the cascade-fragmentation-evaporation model.     

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.     

On the transverse energy distributions in the central rapidity region of 16O+Pb collisions at 200 GeV per nucleon

We point out that the recent data obtained by the NA35 collaboration at the CERN SPS on E_T distributions in ¹⁶O + Pb collisions can be understood within the wounded nucleon model with a simple geometrical calculation of the number of interacting nucleons in ¹⁶O. Although the large E_T trigger increases the average E_T per final state hadron, we are unable to explain in this way the observed rather large value of this quantity.     

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.     

Neutron emission in interactions of 1H, 2H, 4He, and 12C nuclei with lead nuclei at 1–2 GeV per nucleon

The double differential cross sections for neutron production that were measured by the time-of-flight method for interactions of 2-GeV p and d, 4-GeV ⁴He, and 24-GeV ¹²C with Pb nuclei are discussed. In the phenomenological model of four moving sources, the neutron energy distribution shape at emission angles above 30° is well reproduced with the temperature parameters for all sources that are almost independent of the type and the energy of incident nuclei. Using the developed model, we estimate the mean neutron multiplicity and the energy removed by neutron emission.     

A measurement of cross sections for 16O Al and 16O Pb interactions at 60 and 200 GeV/c per nucleon

Cross sections are measured for ¹⁶O collisions with A1 and Pb. Dependences on beam momentum and atomic number are compared with data obtained at much lower beam momenta.     

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.     

Yields and transverse momenta of the 6Li fragments in the emulsion at 4.5 GeV/c per nucleon

We present the results of the study of interaction of the relativistic ⁶Li nucleus with the momentum 4.5 GeV/c per nucleon with the photoemulsion. Yields of the ¹H (³He) and ²H (⁴He) isotopes due to the fragmentation of ⁶Li are found to be almost equal. Cross sections for the charge exchange and pickup reactions are found to be σ_exch=9±2 mb. The distributions of the fragment transverse momenta projected onto the emulsion plane are used to obtain the nucleon Fermi momentum of ⁶Li, P_F, this value being equal to 129±8 MeV/c. The high momentum component in the transverse momentum distributions of ³He and ⁴He isotopes is observed. Received: 4 August 1997