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}

The E864 experiment at the AGS is designed to carry out high sensitivity searches for a variety of possible new particles using relativistic heavy ion Au beams on Pb and Pt targets. In order to reach the desired sensitivities, a level-2 “late energy” trigger was built to select events in which a heavy particle is detected in a hadronic calorimeter with deposited energy and time-of-flight from the target exceeding preset values. The physics motivation for the trigger is discussed and and details of its hardware and software design are given. Performance results from recent E864 data taking runs are presented.

A large hadronic lead scintillating fiber calorimeter has been built and integrated into the AGS experiment E864 [C. Pruneau et al., E864 Collaboration, Proc. 6th Internal. Conf. on Calorimetry in High Energy Physics, 1996, Frascati, Italy; F. Rotondo et al., E864 Collaboration, Proc. Quark Matter'96, Heidelberg, Germany, 20 May 1996] spectrometer to provide an independent measurement of the mass of particles produced in heavy ion collisions. The “spaghetti-type” calorimeter design and construction techniques are described in detail. Results from a prototype and the full implementation of the calorimeter are reported. The hadronic energy resolution of the calorimeter is found to be 6E/E = 0.035(± 0.005) + 0.344(± 0.008)/trE/GeV, in very good agreement with a FLUKA calculation. The hadronic time resolution is measured to be better than 400 ps. The combined calorimeter energy and time signals provide for a mass determination with good resolution. The mass resolution scales as δm/m = 0.026 + 0.347/√E(GeV) for velocities v/c

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}

The production of pions, protons and deuterons is studied at a laboratory angle of 144° in 28 Si+Pb collisions at 14.6 GeV/ c per nucleon. The centrality dependence of the pion yields is studied over the full impact parameter range using a zero degree calorimeter. The results are compared with the hadronic cascade model RQMD. These calculations are generally in agreement with the experimental results. According to these calculations, the pion yield in our acceptance is completely dominated by Δ-decay at freeze-out. Our measurements thus support the importance of baryon resonance production as one of the central features of relativistic heavy ion collisions at AGS energies. Although the strength of the pion spectrum is adequately described for kinetic energies above 50 MeV, an additional very soft component is observed in the pion spectra which is not predicted by RQMD. This very soft component accounts for a significant fraction of the total pion yield in this rapidity range but remains unexplained.

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.

The two-pion correlation function has been measured for charged pions produced in central 14.6 A GeV/ c Si + Pb collisions at the AGS. Data for like-sign pions show a clear quantum interference effect as expected for identical bosons. The experimental correlation function agrees well with that obtained for events generated by a cascade code (RQMD). The present data are consistent with a time-averaged rms freeze-out radius of 8.3 fm and a mean duration of pion emission of 9 fm/ c . The system has expanded considerably before 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.

In this article the authors summarize recent results from the E814 forward spectrometer on proton and pion distributions that give insight into the initial baryon (and energy) density achieved in central collisions as well as the temperature of the system at freeze-out. An independent measure for the latter, complementing the slope constants of particle spectra, is the population of nucleon excited states, in particular the {Delta}(1232) resonance. Besides its influence on the pion spectra it has also been identified directly in the experiment and first results are discussed. The first results from E814 on kaon spectra at low transverse momentum p{sub t} are presented; the spectra show an unexpected very steep rise at the lowest p{sub t}. The two pion correlation function has been studied for positive and negative pions and the authors show that it is consistent with a large source size at freeze-out. Finally, they show that the present data give a consistent picture of a system in thermal and chemical equilibrium at freeze-out.

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.

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.

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.

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.

Transverse momentum distributions of light mass beam rapidity fragments 1 H, 3 He, and 4 He in reactions of 28 Si + Al , Cu and Pb are presented. The widths of the distributions are found to increase with increasing projectile-target overlap. This dependence is not consistent with the observed distributions being associated with the Fermi momentum of the nucleons in the projectile nucleus.

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 have initiated a search for strange quark matter in the products of 14.6 GeV/ c per nucleon 28 Si collisions with nuclei, utilizing the apparatus of E-814 at Brookhaven National Laboratory's AGS. We report the first results of this search, which is sensitive to particles with charge-to-mass ratios between 0.1 and 0.3 (GeV/ c 2 ) −1 that are produced within approximately ±0.5 units of the center of mass rapidity.

We have designed, built, and tested a high-resolution streamer chamber that employs a novel diffusion suppression scheme. The chamber operates at 60 atm, uses a few-nanoseconds-wide 250 kV high-voltage pulse, has a maximum repetition rate of 10 Hz, and has an active volume of 13.5 × 4.5 × 0.7 cm3. Under these conditions we measure the rms deviation of streamer centers from fitted track trajectories to be about 12 ωm in space, and a two-track resolution of approximately 50 ωm.

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.

Previously, K. Bakhtar and E. Sagal [ibid. vol. 17, pp. 4-11, 2002] made remarkable claims for the performance of the Bakhtar Associates ground-penetrating radar (GPR) in detecting and classifying buried unexploded ordnance (UXO). In this article, we report the results of the series of blind tests on the EarthRadar carried out during the Fall of 2000 and Spring of 2001, which led to very different conclusions regarding the radar's performance. The contents of this article are excerpted from the final report on the testing, prepared by the Institute for Defense Analyses.

This report describes a multi-plane drift chamber that was designed and constructed to function as a topological detector for the BNL AGSE896 rare particle experiment. The chamber was optimized for good spatial resolution, two track separation, and a high uniform efficiency while operating in a 1.6 Tesla magnetic field and subjected to long term exposure from a 11.6 GeV/nucleon beam of 10**6 Au ions per second.

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 present the final results from Experiment 864 of a search for charged and neutral strange quark matter produced in interactions of 11.5 GeV/c per nucleon Au beams with Pt or Pb targets. Searches were made for strange quark matter with A>4. Approximately 30 billion 10% most central collisions were sampled and no strangelet states with A, 35 pages, 18 figures, submitted to Phys. Rev. C

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{

Light nuclei can be produced in the central reaction zone via coalescence in relativistic heavy ion collisions. E864 at BNL has measured the production of ten light nuclei with nuclear number of A=1 to A=7 at rapidity $y\simeq1.9$ and $p_{T}/A\leq300MeV/c$. Data were taken with a Au beam of momentum of 11.5 A $GeV/c$ on a Pb or Pt target with different experimental settings. The invariant yields show a striking exponential dependence on nuclear number with a penalty factor of about 50 per additional nucleon. Detailed analysis reveals that the production may depend on the spin factor of the nucleus and the nuclear binding energy as well., (6 pages, 3 figures), some changes on text, references and figures' lettering. To be published in PRL (13Dec1999)

Experiment E864 at the Brookhaven AGS accelerator uses a high sensitivity, large acceptance spectrometer, designed to search for strangelets and other novel forms of matter produced in high-energy heavy ion collisions. The spectrometer has excellent acceptance and rate capabilities for measuring the production properties of known particles and nuclei such as p, d and 6 He . The experiment uses a magnetic spectrometer and employs redundant time of flight and position detectors and a hadronic calorimeter. In this paper we describe the design and performance of the spectrometer.

We have conducted a search for bound states of a negative pion and a number of neutrons (pineuts) using the E814 spectrometer. A beam of {sup 28}Si at a momentum of 14.6{ital A} GeV/{ital c} was used to bombard targets of Al, Cu, Sn, and Pb. We describe our experimental technique, present measured upper limits for pineut production, and discuss the significance of our results.

We present the transverse energy distributions, {ital d}{sigma}/{ital dE}{sub {ital T}} and {ital dE}{sub {ital T}}/{ital d}{eta}, and the charged particle multiplicity distributions, {ital d}{sigma}/{ital dN}{sub {ital c}} and {ital dN}{sub {ital c}}/{ital d}{eta}, produced in {ital p}+Al and {ital p}+Pb collisions at 14.6 GeV/{ital c}. The data exhibit a weak correlation between these global variables. While a significant increase of the mean multiplicity with the mass of the target is observed, the transverse energy distributions show little target dependence. The {ital dE}{sub {ital T}}/{ital d}{eta} distribution shifts backward as the mass of the target increases, indicating the presence of rescattering. The data are compared to the predictions of the relativistic quantum molecular dynamic model (RQMD) and Fritiof event generators. RQMD reproduces well the main features of the data while Fritiof predicts too forward peaked transverse energy and particle multiplicity pseudorapidity distributions.

Inclusive double differential multiplicities [ital d][sup 2][ital N]/[ital dy] d[ital p][sub [ital t]] and related quantities have been measured for protons and deuterons produced in 14.6[ital A] GeV/[ital c] Si+Al and Si+Pb collisions using the E814 forward spectrometer at the AGS at BNL. Collision centrality'' is determined by measuring [ital N][sub [ital c]], the total charged particle multiplicity in the pseudorapidity range 0.85[lt][eta][lt]3.8. For both systems Si + Al and Si + Pb, an increase in the proton rapidity distribution [ital dN]/[ital dy] at midrapidity and a corresponding decrease at higher rapidities are observed with increasing [ital N][sub [ital c]]. For Si+Pb, Boltzmann slope parameters [ital T][sub [ital B]] increase significantly in the most central collisions. The measured distributions exhibit a centrality dependence even when [sigma]/[sigma][sub geo][approx lt]10%, where full overlap between the Si and Pb nuclei occurs in a simple geometric picture. The proton rapidity distribution [ital dN]/[ital dy] is presented for the symmetric system Si+Al over the entire rapididty interval. The total number of protons, which is the integral of this quantity over rapidity, varies with [ital N][sub [ital c]]. Results are compared with various model calculations, mostly using the hadronic cascade codes ARC and RQMD. No significantmore » nuclear transparency is observed, indicating that large baryon and energy densities are produced in these collisions.« less

We present a systematic study of transverse energy ([ital E][sub [ital T]]) production in collisions of 11.4[ital A] GeV/[ital c] Au and 14.6[ital A] GeV/[ital c] Si ions with targets of Al, Au, and Pb. Comparison of data for Au+Au and Si+Al indicates that, for the heavier system, there is an increase in the amount of stopping which is accompanied by a decrease in the width of the [ital dE][sub [ital T]]/[ital d][eta] distribution. The ratio of the maximum [ital E][sub [ital T]] observed for the two systems is significantly greater than the ratio of the total energy available in the center of mass frame.

A high-resolution streamer chamber was built in which the thermal diffusion of the ionization electrons has been suppressed during the trigger formation time. The chamber has been operated in a high-energy beam, and a resolution of 12- mu m was achieved with two measurable streamers per millimeter of track. The chamber cross section is depicted, and measurement results are presented. >