Search

A strangelet search in Si+Pt and Au+Pt collisions at alternating-gradient synchrotron (AGS) energies, using a focusing spectrometer, sensitive to mass per charge of 3-14 GeV/${\mathit{c}}^{2}$ was conducted during the 1992 and 1993 heavy ion runs at the AGS. The null results thereof are presented as upper limits on the invariant production cross section, in the range of ${10}^{\ensuremath{-}5}$-${10}^{\ensuremath{-}4}$ mb ${\mathit{c}}^{3}$/${\mathrm{GeV}}^{2}$, and model dependent sensitivity limits in the range of ${10}^{\ensuremath{-}7}$-${10}^{\ensuremath{-}5}$ per collision. Measurements of the production cross sections of several nonstrange nuclear systems, from $p$ to $^{7}\mathrm{Be}$ and $^{8}\mathrm{Li}$, the background of the strangelet search, are also presented.

Recent estimates suggest that the production of strange exotic objects, such as the hypothetical {ital H} dibaryon ({ital H}), is surprisingly large in Au collisions at AGS energies. Two possible bound states of the {ital H}, namely {ital H}-{sup 3}He and {ital H}-{ital d}, would be well separated in mass from known nuclear isotopes and therefore could be uniquely identified by experiment. We report the null result of a first search for these objects in Au+Pt collisions at the AGS, and limit their production cross sections for stable systems to {similar_to}10{sup {minus}5} mb/(GeV){sup 2}, near {ital y}=0.6 and {ital p}{sub {ital t}}/{ital Z}=0.18 GeV/{ital c}.

During the 1993 AGS heavy ion run, experiment E886 conducted a strangelet search in Au + Pt reactions, with beam momentum of 10.8 GeV/c per nucleon. Presented here are the upper limit for strangelet production, invariant cross sections for p, t, d 3 He, 4 He, 6 He, 8 He, 6 Li, 7 Li, 8 Li and 7 Be, along with a demonstration of their agreement with a coalescence model fit to data collected by E886 during the 1992 engineering run, and upper limits for production cross sections for other rare objects, such as (H dibaryon)-nucleus systems. All results reported here are preliminary.

A review is made of those past, present, and planned experiments at the AGS whose primary purpose is to determine whether the H‐dibaryon exists. Preliminary results are given for experiment E813, based on partially‐completed analysis.

At the Brookhaven AGS several experiments are searching for the unique strangeness S = −2 H-dibaryon with the quark composition (uuddss). The E813/E836 collaboration, in particular, is using a high-intensity, separated 1.8 GeV/c K − beam and two different target configurations. In E836 the reaction K − + 3He→K + + H + n is used to search for a relatively deeply-bound H. Complementary to E836 the reactions K − + p → Ξ − + K +, followed by (Ξ −, d)atom → H + n are used to search near twice the A mass. The status of these two experiments is summarized, and other H-dibaryon searches are briefly reviewed.

Recently, highly relativistic Au beams have become available at the Brookhaven National Laboratory, Alternating Gradient Synchrotron. Inclusive production cross sections for composite particles, d, t, He3, and He4, in 11.5A GeV/c Au+Pt collisions have been measured using a beam line spectrometer. For comparison, composite particle production was also measured in Si+Pt and p+Pt collisions at similar beam momenta per nucleon (14.6A GeV/c and 12.9 GeV/c, respectively). The projectile dependence of the production cross section for each composite particle has been fitted to Aprojα. The parameter α can be described by a single function of the mass number and the momentum per nucleon of the produced particle. Additionally, the data are well described by momentum-space coalescence. Comparisons with similar analysis of Bevalac A+A data are made. The coalescence radii extracted from momentum-space coalescence fits are used to determine reaction volumes (‘‘source size’’) within the context of the Sato-Yazaki model.