Search

We present Experiment 864's measurement of invariant antideuteron yields in 11.5A GeV/c Au + Pt collisions. The analysis includes 250 million triggers representing 14 billion 10% central interactions sampled for events with high mass candidates. We find (1/2 pi pt) d^(2)N/dydpt = 3.5 +/- 1.5 (stat.) +0.9,-0.5 (sys.) x 10^(-8) GeV^(-2)c^(2) for 1.8=0.35 GeV/c (y(cm)=1.6) and 3.7 +/- 2.7 (stat.) +1.4,-1.5 (sys.) x 10^(-8) GeV^(-2)c^(2) for 1.4=0.26 GeV/c, and a coalescence parameter B2-bar of 4.1 +/- 2.9 (stat.) +2.3,-2.4 (sys.) x 10^(-3) GeV^(2)c^(-3). Implications for the coalescence model and antimatter annihilation are discussed., Comment: 8 pages, 4 figures, Latex, submitted to Phys. Rev. Lett

We present results from Experiment 864 for antiproton production and antideuteron limits in Au + Pb collisions at 11.5 GeV/c per nucleon. We have measured invariant multiplicities for antiprotons for rapidities 1.4{lt}y{lt}2.4 at low transverse momentum as a function of collision geometry. When compared with the results from Experiment 878 our measurements suggest a significant contribution to the measured antiproton yield from the decay of strange antibaryons. We have also searched for antideuterons and see no statistically significant signal. Thus, we set upper limits on the production at approximately 3{times}10{sup {minus}7} per 10{percent} highest multiplicity Au+Pb interaction. {copyright} {ital 1999} {ital The American Physical Society}

We present results of a search for strange quark matter (strangelets) in 11.5 A GeV/c Au+Pb collisions from the 1994 and 1995 runs of experiment E864 at Brookhaven's AGS. We observe no strangelet candidates and set a 90% confidence level upper limit of approximately 3x10**-8 per 10% central interaction for the production of |Z|=1 and |Z|=2 strangelets over a large mass range and with metastable lifetimes of about 50 ns or more. These results place constraints primarily on quark-gluon plasma based production models for strangelets.

We present the first results from the E864 Collaboration on the production of antiprotons in 10{percent} central 11.5A GeV /c Au+Pb nucleus collisions at the Brookhaven Alternating Gradient Synchrotron. We report invariant multiplicities for antiproton production in the kinematic region 1.4{lt}y{lt}2.2 and 50{lt} p{sub T}{lt} 300 MeV/c , and compare our data with a first collision scaling model and previously published results from the E878 Collaboration. The differences between the E864 and E878 antiproton measurements and the implications for antihyperon production are discussed. {copyright} {ital 1997} {ital The American Physical Society}

An investigation of the production of neutron-rich isotopes from the fragmentation of {sup 28}Si projectiles at {ital p}{sub lab}=14.6 GeV/{ital c} per nucleon was performed using the BNL-AGS-E814 spectrometer. We have measured the inclusive production cross sections of neutron-rich fragments ({sup 6}He, {sup 8}He, {sup 8}Li, {sup 9}Li, {sup 10}Be, {sup 11}Be, and {sup 13}B). We have also measured the transverse momentum distributions for {sup 6}He and {sup 9}Li, and the forward and transverse energy distributions associated with {sup 6}He production. The momentum distributions were analyzed in the context of the Goldhaber model. The question of whether the fragments are produced in the decay of the projectile following its electromagnetic excitation was also investigated.

We have studied in detail the electromagnetic dissociation of [sup 28]Si projectiles at 14.6 GeV/([ital c] nucleon), interacting with Pb, Sn, Cu, and Al targets. Exclusive cross sections were measured for several decay channels, including final states involving the emission of protons, neutrons, and [alpha] particles. Excitation energy distributions for the 1[ital n]+[sup 27]Si and 2[ital p]+[sup 26]Mg decay channels were reconstructed with a resolution of 2 MeV, using a constrained kinematic fit. The energy distributions obtained for 1[ital n]+[sup 27]Si are in good agreement with the [sigma]([gamma],[ital n]) photoneutron cross sections multiplied by the virtual photon spectrum obtained in the Weizsaecker-Williams approximation. A search for the double photon excitation process, based on the dependence of the cross sections on the target atomic number, was performed.

We have measured cross sections for the synthesis of nuclei of mass [ital A][le]4 in collisions of 14.6[ital A] GeV/[ital c] [sup 28]Si nuclei with targets of Pb, Cu, and Al. The data are measured at close to center-of-mass rapidities, and are unique in their exploration of the centrality dependence of nucleosynthesis. Simple coalescence models that were used to study nucleosynthesis at lower energies are inadequate for the description of our measurements. Our data and improved models are used to extract parameters related to the size of the interaction volume at freeze-out.

We present the results of an analysis of two charged particle and transverse energy correlations in Si+Pb collisions at BNL AGS at 14.6 GeV/{ital c} per nucleon. The measured semi-inclusive normalized two particle pseudorapidity corrleation function exhibits short range correlations similar to the correlations observed in hadron-hadron and hadron-nucleus collisions at higher energies, although the observed correlations are smaller than the values scaled from {ital hp} and {ital hA} data. Estimates, provided by the observed correlations, of the intermittency indices as well as of the parameters of the cluster model are presented. Predictions using the FRITIOF event generator, which at this level of statistical accuracy show no pseudorapidity correlations, are not in agreement with our data. Azimuthal angle two particle correlations show nonzero back-to-back correlations in the central region (consistent with FRITIOF predictions) and are almost flat in the projectile fragmentation region. We also present results on the transverse energy azimuthal correlation function, which are similar to those from the two particle correlation function.

We have measured antiproton production cross sections as functions of centrality in collisions of 14.6 GeV/[ital c] per nucleon [sup 28]Si ions with targets of Al, Cu, and Pb. For all targets, the antiproton yields increase linearly with the number of projectile nucleons that have interacted, and show little target dependence. We discuss the implications of this result on the production and absorption of antiprotons within the nuclear medium.

We report a direct measurement of the final-state energy spectrum in the electromagnetic dissociation of {sup 28}Si into {ital p}+ {sup 27}Al at an energy of 14.6 GeV/nucleon. The final-state energy is obtained through a calculation of the {ital p}-{sup 27}Al invariant mass in kinematically reconstructed events. The final-state energy spectrum for all targets is peaked near the isovector giant-dipole resonance in {sup 28}Si and the dependence of the magnitude of the cross section on target charge confirms that the excitation is largely electromagnetic. By exploiting the expected scaling behavior on target {ital Z} and {ital A}, the background from nuclear interactions is evaluated and subtracted, leaving a pure electromagnetic dissociation final-state energy distribution. This distribution is well reproduced by simulated events, in which the photon spectrum calculated in the Weiszaecker-Williams approximation is combined with experimental data on the photonuclear reaction {sup 28}Si({gamma},{ital p}) {sup 27}Al, and slight differences are observed only at low final-state energy.

We present measurements from BNL AGS Experiment 864 of the $_{\ensuremath{\Lambda}}^{3}\mathrm{H}$ yield and of an upper limit on the $_{\ensuremath{\Lambda}}^{4}\mathrm{H}$ yield in central $11.5A\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c\phantom{\rule{0.3em}{0ex}}\text{Au}+\text{Pt}$ collisions. The measurements span a rapidity range from center of mass, ${y}_{\mathrm{c.m.}}$, to ${y}_{\mathrm{c.m.}}+1$ and a transverse momentum range of $0l{p}_{t}\ensuremath{\leqslant}1.5\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$. We compare these results with E864 measurements of stable light nuclei and particle unstable nuclei yields of the same baryon number. The implications of these results for the coalescence of strange clusters are discussed.

We report measurements from experiment E864 at the BNL-AGS of the yields of particle unstable light nuclei in central collisions of ${}^{197}\mathrm{Au}$ with beam momentum of $11.5A$ $\mathrm{GeV}/c$ on ${}^{197}\mathrm{Pt}.$ Yields are reported as a function of rapidity for the nuclei ${}^{4}\mathrm{H},$ ${}^{4}\mathrm{Li},$ ${}^{5}\mathrm{He},$ and ${}^{5}\mathrm{Li}$ in the rapidity range from ${y}_{\mathrm{c}.\mathrm{m}.}$ to ${y}_{\mathrm{c}.\mathrm{m}.}+0.8$ and in the transverse momentum range of approximately $0.1l~{p}_{T}/Al~0.4\mathrm{GeV}/c.$ The yields are compared to previously reported yields and trends for the production of stable light nuclei. The nonobservation of two excited states ${}^{5}{\mathrm{He}}_{16.75\mathrm{MeV}}^{*}$ and ${}^{5}{\mathrm{Li}}_{16.66\mathrm{MeV}}^{*}$ is used to set an upper limit on the yields of these states.

We report on measurements by the E864 experiment at the BNL-AGS of the yields of light nuclei in collisions of {sup 197}Au with beam momentum of 11.5A GeV/c on targets of {sup 208}Pb and {sup 197}Pt. The yields are reported for nuclei with baryon number A=1 up to A=7, and typically cover a rapidity range from y{sub c.m.} to y{sub c.m.}+1 and a transverse momentum range of approximately 0.1{