Antiproton Yields Research Articles

Scaling properties of proton and antiproton production in sqrt[s(NN)]=200 GeV Au+Au collisions.

We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in Au+Au collisions at sqrt[s(NN)]=200 GeV measured at midrapidity by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider. In central collisions at intermediate transverse momenta (1.5<p(T)<4.5 GeV/c) a significant fraction of all produced particles are protons and antiprotons. They show a centrality-scaling behavior different from that of pions. The pmacr;/pi and p/pi ratios are enhanced compared to peripheral Au+Au, p+p, and e(+)e(-) collisions. This enhancement is limited to p(T)<5 GeV/c as deduced from the ratio of charged hadrons to pi(0) measured in the range 1.5<p(T)<9 GeV/c.

Systematic study of Au–Au collisions with AGS experiment E917

The systematics of baryon stopping and strange particle production have been studied in Au+Au collisions at 6, 8, and 10.8 GeV per nucleon with AGS experiment E917. In particular, the systematic behavior of the proton yields, phi meson production, and the yields of antilambdas and antiprotons are examined as functions of beam energy and centrality.

New insight into antiproton production and reabsorption using proton–nucleus collisions at the AGS

Antiproton ($\bar{p}$) yields are presented for proton-nucleus collisions, with targets Be, Cu, and Au, at beam momenta of 12.3 and 17.5 GeV/c. In addition to target size and beam momentum, the number of projectile collisions $\nu$, as derived from the number of ``grey'' tracks (slow protons and deuterons), is used to disentangle the $\bar{p}$ reabsorption from the production. By quantifying the amount of reabsorption of the $\bar{p}$ within the nucleus as a function of $\nu$, the annihilation within the nucleus is estimated and compared to the free annihilation cross section. Preliminary results on antilambda ($\bar{\Lambda}$) production as a function of $\nu$ are also presented for comparison.

Regeneration of anti-protons in ultrarelativistic heavy-ion collisions

The production and annihilation of antiprotons in the hadronic phase of heavy-ion collisions is evaluated within a thermal equilibrium approach. It is shown that the inverse reaction of $p\bar p$ annihilation (i.e., multi-pion annihilation $N_\pi \pi\to p\bar p$ with $N_\pi\simeq$~5-7) in connection with oversaturation of pion phase space (i.e., finite pion chemical potentials) plays an important role in understanding the observed antiproton yields at SpS energies within the standard picture of subsequent chemical and thermal freezeout. Implications for RHIC energies are also addressed.

Antilambda production in Au+Au collisions at 11.7A GeV/c.

We present results for antilambda and antiproton production in Au+Au collisions at 11.7 A GeV/c including spectra and extracted invariant yields for both species in central and peripheral collisions in the rapidity range 1.0<y<1.4. The antilambda yield increases from dN(Lambda;)/dy = 1.2(+0.7+0.2)(-0.6-0.2)x10(-3) in peripheral collisions to 19(+4+3)(-5-2)x10(-3) in central collisions. The direct antiproton yield is deduced from the measured total antiproton spectra to extract the ratio of antilambda-to-direct-antiproton production. The Lambda/p ratio near midrapidity increases from 0.26(+0.19+0.5)(-0.15-0.4) in peripheral collisions to 3.6(+4.7+2.7)(-1.8-1.1) in central collisions, a value larger than current theoretical estimates.

Covariance of antiproton yield and source size in nuclear collisions

We confront for the first time the widely-held belief that combined event-by-event information from quark gluon plasma signals can reduce the ambiguity of the individual signals. We illustrate specifically how the measured antiproton yield combined with the information from pion-pion HBT correlations can be used to identify novel event classes.

Results from Experiment E917 for Au + Au Collisions at the AGS*1

The effects of baryon stopping and its resulting energy deposition on the dynamics of Au + Au collisions at 6, 8 and 10.8 GeV/nucleon are explored with recent results from the AGS experiment E917. Current analyses of stopping, collective flow signals and HBT parameters are presented. Strangeness and anti-baryon production is examined using the yields of anti-lambdas and anti-protons.

Results from experiment E917 for Au + Au collisions at the AGS

The effects of baryon stopping and its resulting energy deposition on the dynamics of Au + Au collisions at 6, 8 and 10.8 GeV/nucleon are explored with recent results from the AGS experiment E917. Current analyses of stopping, collective flow signals and HBT parameters are presented. Strangeness and anti-baryon production is examined using the yields of anti-lambdas and anti-protons.

Antideuteron yield and coalescence implications at the AGS

We present the preliminary results of Experiment 864's search for antideuterons in 11.5 GeV/c per nucleon Au + Pt collisions at the AGS. The data represents 14 billion 10% central interactions selectively triggered for events with high mass candidates. Antideuteron invariant yields are found to be 3.5 ± 1.5( stat.) +0.9 −0.5( sys.) × 10 −8 GeV −2 c 2 in the rapidity range between y = 1.8 and 2.2 ( y cm = 1.6) for 〈 p t 〉= 0.35 GeV/c and 3.7±2.7( stat.) +1.4 −1.5( sys.) × 10 −8 GeV −2 c 2 between rapidities y = 1.4 and 1.8 at 〈 p t 〉= 0.26 GeV/c. These yields, along with E864 antiproton measurements, lead to a most probable value for the coalescence factor B 2 of 4.1 ± 2.9( stat.) +2.3 −2.4( sys.) × 10 −3 GeV −2 c 3 after correcting antiproton yields for antihyperon feeddown contributions. Implications for the coalescence model and antimatter annihilation from an antideuteron measurement are also discussed.

Cosmic Antiprotons as a Probe for Supersymmetric Dark Matter?

The flux of cosmic ray antiprotons from neutralino annihilations in the galactic halo is computed for a large sample of models in the MSSM (the Minimal Supersymmetric extension of the Standard Model). We also revisit the problem of estimating the background of low-energy cosmic ray induced secondary antiprotons, taking into account their subsequent interactions (and energy loss) and the presence of nuclei in the interstellar matter. We consider a two-zone diffusion model, with and without a galactic wind. We find that, given the uncertainties in the background predictions, there is no need for a primary (exotic) component to explain present data. However, allowing for a signal by playing with the uncertainties in the background estimate, we discuss the characteristic features of the supersymmetric models which give a satisfactory description of the data. We point out that in some cases the optimal kinetic energy to search for a signal from supersymmetric dark matter is above several GeV, rather than the traditional sub-GeV region. The large astrophysical uncertainties involved do not, one the other hand, allow the exclusion of any of the MSSM models we consider, on the basis of data. We present besides numerical results also convenient parameterizations of the antiproton yields of all `basic' two-body final states. We also give examples of the yield and differential energy spectrum for a set of supersymmetric models with high rates. We also remark that it is difficult to put a limit on the antiproton lifetime from present measurements, since the injection of antiprotons from neutralino annihilation can compensate the loss from decay.

Antiproton production and antideuteron production limits in relativistic heavy ion collisions

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<y<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 x 10^{-7} per 10% highest multiplicity Au + Pb interaction.

Search for positively charged strangelets and other related results with E864 at the AGS

We report on the latest results in the search for positively charged strangelets from the E864 96/97 run at the AGS with sensitivity of about 8 × 10−9 per central collision. This contribution also contains new results of a search for highly charged strangelets with Z = +3. Production of light nuclei, such as 6He and 6Li, is presented as well. Measurements of yields of these rarely produced isotopes near midrapidity will help constrain the production levels of strangelets via coalescence. E864 also measures antiproton production which includes decays from antihyperons. Comparisons with antiproton yields measured by E878 as a function of centrality indicate a large antihyperon-to-antiproton ratio in central collisions.

Antiproton Production inAu+AuCollisions at11.7AGeV/c

Antiproton production in 11.7AGeV/c Au+Au collisions over a wide transverse-mass coverage was studied using the AGS-E866 experimental apparatus. The mean transverse kinetic energy increases as a function of centrality and is similar to that of protons. The antiproton yields in Si+Al, Si+Au, and Au+Au collisions are consistent with scaling with the 0.7 power of the number of participant nucleons.Received 7 May 1998DOI:https://doi.org/10.1103/PhysRevLett.81.2650©1998 American Physical Society

Proton and antiproton distributions at midrapidity in proton-nucleus and sulphur-nucleus collisions

Experiment NA44 has measured proton and antiproton distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and 450GeV/c per nucleon respectively. The inverse slopes of transverse mass distributions increase with system size for both protons and antiprotons but are slightly lower for antiprotons. This could happen if antiprotons are annihilated in the nuclear medium. The antiproton yield increases with system size and centrality and is largest at midrapidity. The proton yield also increases with system size and centrality, but decreases from backward rapidity to midrapidity. The stopping of protons at these energies lies between the full stopping and nuclear transparency scenarios. The data are in reasonable agreement with RQMD predictions except for the antiproton yields from sulphur-nucleus collisions.Received 25 August 1997DOI:https://doi.org/10.1103/PhysRevC.57.837©1998 American Physical Society

Antiproton production and antideuteron limits from experiment E864

In this paper we review preliminary data from experiment 864 for antiprotons and antideuterons produced in Au + Pb collisions at 11.6 A GeV c−1, as reported at strangeness and quark matter conference in 1997. We have measured the invariant multiplicity of antiprotons above midrapidity and at low transverse momentum. Comparisons with previously published antiproton yields from experiment E878 show a significant discrepancy. One possible explanation of this could be the contributions from strange antibaryons whose decay product antiprotons are accepted in our experiment. We also present upper limits on the production of antideuterons.

Centrality dependence of antiproton production in Au+Au collisions.

We have measured the yields of antiprotons in Au+Au interactions in the rapidity range 1.2{lt}{ital y}{lt}2.8 as a function of centrality using a beam line spectrometer. The shapes of the invariant multiplicity distributions at {ital p}{sub {ital t}}=0 are used to explore the dynamics of antiproton production and annihilation. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

Charged hadron distributions in pA and AA collisions at the CERN SPS

Single particle distributions of π ±, K ±, p, p and d near mid-rapidity from 450 GeV/c pA and 200 GeV/c per nucleon SA collisions are presented. Inverse slope parameters are extracted from the transverse mass spectra, and examined for indications of collective phenomena. Proton and antiproton yields are determined for different projectile-target combinations. First results from 160 GeV/c per nucleon PbPb collisions are presented.

Hadrons in dense matter

The properties of hadrons in dense matter are reviewed. Incorporating these medium effects in the relativistic transport model, which treats consistently the change of hadron masses and energies in dense matter via the scalar and vector fields, heavy-ion collisions at SIS energies are studied. This model is seen to provide satisfactory explanations for the observed enhancement of kaon, antikaon, and antiproton yields as well as the enhanced soft pions in the transverse direction. More direct verifications of changing hadron properties in dense matter through the dilepton invariant mass spectra from heavy-ion collisions are also discussed.

Mass dependence of antiproton production in nucleus-nucleus collisions at 3.65 GeV/nucleon

Antiproton production cross-sections have been measured for p+C, C+C, C+Cu and C+Pb collisions at 3.65 GeV/nucleon.\(\bar p\) laboratory momentum and angle are 0.8 GeV/c and 24°. The target mass dependence parameter is found to be 0.43±0.1. A strong increase in antiproton yield is observed from p+C, d+C to C+C collisions. Projectile mass parameter is 1.2±0.2 for d+C to C+C. The construction and calibration of APAKI, an annihilation detector for\(\bar p\) identification, are also described.

Estimates of antiproton production and annihilation in relativistic nucleus-nucleus collisions.

We describe a simple model developed to study the production and annihilation of antiprotons in nucleus-nucleus collisions. The model can be used to calculate the antiproton yields as functions of global observables such as multiplicity, transverse energy, and zero degree energy. We discuss the predictions of the model, and its relevance to the antiproton measurements at the Brookhaven National Laboratory Alternating Gradient Synchrotron facility.