B. Hong

Measurement of pion enhancement at low transverse momentum and of the Δ resonance abundance in Si-nucleus collisions at AGS energy

Abstract We present measurements of pion transverse momentum ( p t ) spectra in central Si-nucleus collisions in the rapidity range 2.0 y p t down to and including p t = 0. The data exhibit an enhanced pion yield at low p t compared to what is expected for a purely thermal spectral shape. This enhancement is used to determine the Δ resonance abundance at freeze-out. The results are consistent with a direct measurement of the Δ resonance yield by reconstruction of proton-pion pairs and imply a temperature of the system at freeze-out close to 140 MeV.We present measurements of the pion transverse momentum (p_t) spectra in central Si-nucleus collisions in the rapidity range 2.0<y<5.0 for p_t down to and including p_t=0. The data exhibit an enhanced pion yield at low p_t compared to what is expected for a purely thermal spectral shape. This enhancement is used to determine the Delta-resonance abundance at freeze-out. The results are consistent with a direct measurement of the Delta-resonance yield by reconstruction of proton-pion pairs and imply a temperature of the system at freeze-out close to 140 MeV.

Two-particle correlations in Au+Au collisions at AGS energy

Two-particle correlation functions have been measured in Au+Au collisions at the AGS. The one-dimensional correlations are compared to the RQMD predictions. A multidimensional analysis of two-pion correlations allows to extract the average phase space density of pions at freeze-out and the pion source velocity.

Directed flow of antiprotons in Au+Au collisions at AGS

Abstract Directed flow of antiprotons is studied in Au+Au collisions at a beam momentum of 11.5A GeV/c. It is shown that antiproton directed flow is anti-correlated to proton flow. The measured transverse momentum dependence of the antiproton flow is compared with predictions of the RQMD event generator.

Directed flow and particle production in Au+Au collisions from experiment E877 at the AGS

In this article we summarize recent results on the study of Au+Au collisions at 10.8A GeV/c obtained at the AGS by the E877 Collaboration. New results on the directed sideward flow are presented. In particular, the dependence of proton and pion production on the direction of the reaction plane will be discussed. It is shown that the sideward flow is mainly due to nucleons and that pions show little flow effects. Two-pion correlation functions are studied to derive the density at freeze-out. Further, we inspect the correlations as a function of the pion direction relative to the reaction plane. A dependence of the deduced source sizes on the pair direction and momentum is observed. The measured source sizes are compared to results obtained in lighter systems. Measured m{sub t} spectra of pions and kaons are also presented. The pion spectra show an enhancement at low m{sub t} similar to that observed in Si+Pb and which was attributed to {triangle} resonance excitation. However, in contrast to Si+Pb now a clear difference between the {pi}{sup +} and {pi}{sup -} spectra is seen. The K{sup +} spectra, which showed a very steep component over a small p{sub t} range in the previously studiedmorexa0» Si+Pb reaction exhibit for Au+Au an unexpected structure at very low p{sub t}.«xa0less

Hadron yields and spectra in Au+Au collisions at the AGS

Abstract Inclusive double differential multiplicities and rapidity density distributions of hadrons are presented for 10.8·A GeV/c Au+Au collisions as measured at the AGS by the E877 collaboration. The results indicate that large amounts of stopping and collective transverse flow effects are present. The data are also compared to the results from the lighter Si+Al system.

Baryon distributions in ultrarelativistic nucleus-nucleus collisions

We have measured distributions in transverse momentum and rapidity of protons from interactions of 14.6 GeV/nucleon28Si projectiles with targets of Al and Pb. The transverse momentum spectra exhibit a thermal shape with a rapidity dependent temperature parameter. For very central or violent collisions the proton rapidity distributions exhibit the large rapidity shifts and (for Si+Al) a peak at midrapidity as required for full stopping.

Recent results from experiment 814 at Brookhaven

Abstract Recent results from the E814 collaboration are presented for reactions of 14.6 GeV/nucleon 28 Si projectiles with targets of Al, Cu, and Pb. This includes transverse energy distributions over the full solid angle and the distribution of charged particle multiplicity in the forward hemisphere. Furthermore we present recent results on transverse momentum spectra and rapidity distributions for protons and discuss them in terms of stopping and/or transparency. A fraction of nucleons emerges at beam rapidity, even for the most central collisions. These ‘punch-through’ distributions are shown to yield information on the in-medium nucleon-nucleon cross section. Finally, we discuss antiproton production at 0° as a function of event centrality to shed some light on possible reabsorption.

Recent results from E877 for Au+Au collisions at AGS energy

Abstract The E877 experiment was dedicated to the study of hadron distributions in Au+Au collisions at the AGS. Here, we will mainly present results from the analysis of the data obtained from the last data taking run, which took place in the fall of 1995 and recorded 46 millions Au+Au events at 11.5 AGeV/c. The improved experimental apparatus and large statistics allowed to extend our previous measurements of particle flow [1–4] to K + , K − , p and Λ. We will also report our latest results on two-particle correlations of like and unlike particles, as well as the measurements of double differential multiplicities of Λ-hyperons.

Flow studies at 10.8 GeV/nucleon

Abstract We present the present status of the E877 studies of anisotropic transverse flow at the AGS energy. Flow is quantified by Fourier analysis of the azimuthal distributions of transverse energy and charged particle multiplicity. Additionally, the mean transverse momentum of identified particle spectra with respect to the reaction plane are measured near the beam rapidity. Analysis shows the presence of nucleon flow at AGS energies and a small pion flow in the direction opposite to that of the nucleon.

Antiproton production in 28Si-Nucleus interactions

Abstract We have used the E814 apparatus to make a systematic study of antiproton production in collisions of 28 Si ions at 14.6 GeV/ c per nucleon with targets of Pb, Cu, and Al. We have measured the antiproton yield per interaction as a function of transverse energy and have found the yield to increase by a factor of ≈ 2 in going from the least to the most central collisions on the Pb target. A simple first-collision picture of antiproton production predicts the yield to increase by a factor of ≈ 11. We suggest that the discrepancy may result from the annihilation of antiprotons within the nuclear medium.