Y. Akiba

Recent results from E802 and E859

Abstract Recent single-particle inclusive measurements and two-particle correlation data from E802 and its succesor, E859, are presented. The K + / π + ratio observed for collisions of 14.6 A·GeV 28 Si ions on various targets is presented as a function of both forward and transverse energy. Source sizes are determined via interferometry using π + , π − , K + and proton pairs.

Antiproton production in 14.6 AGeVc Si+A collisions

Abstract Antiproton production cross sections have been measured for minimum bias and central Si+Al and Si+Au collisions at 14.6 A GeV c . The data presented cover the range of transverse momentum from 0.3 to 1.2 GeV c and lab rapidities from 1.1 to 1.7 units. The relative p π − and p K − yields are found to be the smallest for the heaviest system measured, central Si+Au collisions. For these collisions, the p π − ratio, determined from integrated yields for 1.1⩽y⩽1.7, is (0.84±0.07)×10−3. In the same rapidity interval, the average antiproton inverse m⊥ slope is 141±14 MeV for central Si+Al and central Si+Au collisions.

Centrality dependence of K+ and π+ multiplicities from Si + A collisions at 14.6 A GeV/c☆

Abstract K + and π + multiplicities have been measured in magnetic spectrometer for Si++ Al, Si+ Cu and Si + Au collisions at 14.6 A GeV/ c incident momentum. The multiplicities were obtained for five different windows of forward kinetic energy as detected in a zero degree calorimeter. The K + / π + multiplicity ratio ranges from ≈9% in peripheral interactions to 19% in central Si+Au. The largest K + / π + ratios are observed for those events for each target that leave the least energy in the zero degree calorimeter and the ratio increases with target mass. The observations suggest that multiple interactions are important in the particle production mechanism.

Global transverse energy distributions in Si+Al, Au at 14.6A GeV/c and Au+Au at 11.6A GeV/c

Abstract Measurements of the global transverse energy distributions dσ / dE T and dE T / dη using the new AGS beam of 197 Au at 11.6 A GeV/ c on a Au target, as well as a beam of 28 Si at 14.6 A GeV/ c on Al and Au targets, are presented for a leadglass detector with acceptance 1.3 ≤ η ≤ 2.4 and 0 ≤ φ π . The dσ / dE T spectra are observed to have different shapes for the different systems and simple energy rescaling does not account for the projectile dependence. The Au+Au dσ / dE T spectrum is satisfactorily constructed from the upper edge of Si+Au by the geometric Wounded Projectile Nucleon Model after applying a correction for the beam energy.

Recent results from experiment 859 at the BNL AGS

Abstract This paper presents recent results from Experiment 859 at the BNL AGS, focussing on strangeness ( K ± , Λ, Λ ), rare probes ( p , φ) and two-particle correlations. Highlights of the paper include an analysis of the centrality dependence of K ± yields in terms of the number of participants, a brief review of the current status of the E859 Λ and Λ data, an analysis of the target dependence of p yields in terms of p K − ratios, results of a re-analysis of Λ feed-down contamination of p s, a comparison of the cenal Siue5f8Au and pue5f8p φ yields through the φ K − ratio, an extremely preliminary study of the centrality dependence of the φ line-shape, a summary of the centrality dependence of two-π correlation source sizes, and a comparison of results from two-dimensional analyses of the two-π and two-K + correlation functions.

Target rapidity proton distributions for SI+A collisions at the AGS

Preliminary results are presented for the production of protons in 14.6 A{center dot}GeV/c Si+Al and Si+Au collisions measured by the E859 Phoswich Array at the BNL AGS. The proton data presented cover the laboratory angles of 50--130 degrees and kinetic energies of 40--180 MeV. Slopes and integrated distributions are extracted and comparisons with other experimental data are discussed.

Search for right-handed currents in the decay K+--> micro+ nu.

The longitudinal polarization of the muon emitted in the decay K-italic/sup +/..--> mu../sup +/..nu.. was measured to search for right-handed weak currents in a strangeness-changing process. The 236-MeV/c-italic muons from the decay of stopped K-italic/sup +/ were identified and were collected by a magnetic spectrometer. The muons were then slowed down in a carbon degrader and were brought to rest in an aluminum target. The muon spins were precessed by a 220-G transverse field, and a muon-spin-rotation technique was employed to measure the muon-spin polarization. The polarization was determined to be -0.970 +- 0.047, which is consistent with the V-italic-A-italic hypothesis.

Study of the radiative decay K + → μ + νγ

The radiative decay K/sup +/..--> mu../sup +/..nu gamma.. has been studied by a high-resolution magnetic spectrometer combined with a NaI(Tl) photon detector system. The momentum spectrum of muon from this decay mode was measured in the region 214.5

Formation of sigma hypernuclei from K̄ absorption at rest (observation of a candidate for the LS doublet)

Pions detected from K− reactions in (CH)n (plastic scintillator) tar reveals a sharp peak at a pion momentum ‐185 MeV/c which is indicative of the Σ+→nπ+ decay. This peak is a candidate for a P3/2‐ P1/2 doublet Σ− hypernucleus. (AIP)

The centrality dependence of the source size for AuAu collisions at the AGS

Abstract Recent π − π − correlation measurements and deuteron to proton yield ratio measurements for Auue5f8Au collisions from Brookhaven E866 are presented. These measurements allow us, with some interpretation, to deduce the size of the participant region in a heavy ion collision. An unpredicted rise of the apparent source size is seen in the π − π − data at midrapidity. No corresponding drop in the deuteron to proton yield ratio is seen. Further experimental study is needed to improve the statistical significance of the correlation result and to determine whether it can be explained by conventional hadronic means.