1,144 research outputs found
Longitudinal Momentum Fraction X_L for Two High P_t Protons in pp->ppX Reaction
We present an analysis of new data from Experiment E850 at BNL. We have
characterized the inclusive cross section near the endpoint for pp exclusive
scattering in Hydrogen and in Carbon with incident beam energy of 6 GeV. We
select events with a pair of back-to-back hadrons at large transverse momentum.
These cross sections are parameterized with a form
, where is the ratio of the longitudinal momentum
of the observed pair to the total incident beam momentum. Small value of
may suggest that the number of partons participating in the reaction is large
and reaction has a strong dependence on the center-of-mass energy. We also
discuss nuclear effects observed in our kinematic region.Comment: 4 pages, 2 figures, to be published in Proceedings of CIPANP2000,
Quebec, May 22-28, 2000, requires aipproc.sty(included
Beam-Energy and System-Size Dependence of Dynamical Net Charge Fluctuations
We present measurements of net charge fluctuations in Au+Au collisions at √sNN=19.6, 62.4, 130, and 200 GeV, Cu+Cu collisions at √sNN=62.4 and 200 GeV, and p+p collisions at √s=200GeV using the dynamical net charge fluctuations measure ν+−,dyn. We observe that the dynamical fluctuations are nonzero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate 1/Nch scaling but display approximate 1/Npart scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation
Energy and System Size Dependence of ϕ Meson Production in Cu + Cu and Au + Au Collisions
We study the beam-energy and system-size dependence of ϕ meson production (using the hadronic decay mode ϕ → K + K − ) by comparing the new results from Cu + Cu collisions and previously reported Au + Au collisions at √sNN = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented in this Letter are from mid-rapidity ( | y | \u3c 0.5 ) for 0.4 \u3c PT \u3c 5 GeV /c . At a given beam energy, the transverse momentum distributions for ϕ mesons are observed to be similar in yield and shape for Cu + Cu and Au + Au colliding systems with similar average numbers of participating nucleons. The ϕ meson yields in nucleus–nucleus collisions, normalized by the average number of participating nucleons, are found to be enhanced relative to those from p + p collisions. The enhancement for ϕ mesons lies between strange hadrons having net strangeness =1 ( K− and Λ ¯ ) and net strangeness =2 (Ξ). The enhancement for ϕ mesons is observed to be higher at √sNN = 200 GeV compared to 62.4 GeV. These observations for the produced ϕ ( ss ¯ ) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus–nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems
Energy Dependence of Nuclear Transparency in C(p,2p) Scattering
The transparency of carbon for (p,2p) quasi-elastic events was measured at
beam energies ranging from 6 to 14.5 GeV at 90 degrees c.m. The four momentum
transfer squared q*q ranged from 4.8 to 16.9 (GeV/c)**2. We present the
observed energy dependence of the ratio of the carbon to hydrogen cross
sections. We also apply a model for the nuclear momentum distribution of carbon
to normalize this transparency ratio. We find a sharp rise in transparency as
the beam energy is increased to 9 GeV and a reduction to approximately the
Glauber level at higher energies.Comment: 4 pages, 2figures, submitted to PR
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Bulk properties of the system formed in Au+Au collisions at sNN =14.5 GeV at the BNL STAR detector
We report systematic measurements of bulk properties of the system created in Au+Au collisions at sNN=14.5 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum spectra of π±, K±, and p(p) are studied at midrapidity (|y|<0.1) for nine centrality intervals. The centrality, transverse momentum (pT), and pseudorapidity (η) dependence of inclusive charged particle elliptic flow (v2), and rapidity-odd charged particles directed flow (v1) results near midrapidity are also presented. These measurements are compared with the published results from Au+Au collisions at other energies, and from Pb+Pb collisions at sNN=2.76 TeV. The results at sNN=14.5 GeV show similar behavior as established at other energies and fit well in the energy dependence trend. These results are important as the 14.5-GeV energy fills the gap in μB, which is of the order of 100 MeV, between sNN=11.5 and 19.6 GeV. Comparisons of the data with UrQMD and AMPT models show poor agreement in general
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Measurements of the transverse-momentum-dependent cross sections of J /ψ production at mid-rapidity in proton+proton collisions at s =510 and 500 GeV with the STAR detector
We present measurements of the differential cross sections of inclusive J/ψ meson production as a function of transverse momentum (pTJ/ψ) using the μ+μ- and e+e- decay channels in proton+proton collisions at center-of-mass energies of 510 and 500 GeV, respectively, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The measurement from the μ+μ- channel is for
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Measurement of inclusive J/ψ suppression in Au+Au collisions at sNN=200 GeV through the dimuon channel at STAR
J/ψ suppression has long been considered a sensitive signature of the formation of the Quark-Gluon Plasma (QGP) in relativistic heavy-ion collisions. In this letter, we present the first measurement of inclusive J/ψ production at mid-rapidity through the dimuon decay channel in Au+Au collisions at sNN=200 GeV with the STAR experiment. These measurements became possible after the installation of the Muon Telescope Detector was completed in 2014. The J/ψ yields are measured in a wide transverse momentum (pT) range of 0.15 GeV/c to 12 GeV/c from central to peripheral collisions. They extend the kinematic reach of previous measurements at RHIC with improved precision. In the 0-10% most central collisions, the J/ψ yield is suppressed by a factor of approximately 3 for pT>5 GeV/c relative to that in p+p collisions scaled by the number of binary nucleon-nucleon collisions. The J/ψ nuclear modification factor displays little dependence on pT in all centrality bins. Model calculations can qualitatively describe the data, providing further evidence for the color-screening effect experienced by J/ψ mesons in the QGP
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Charge-dependent pair correlations relative to a third particle in p + Au and d + Au collisions at RHIC
Quark interactions with topological gluon configurations can induce chirality imbalance and local parity violation in quantum chromodynamics. This can lead to electric charge separation along the strong magnetic field in relativistic heavy-ion collisions – the chiral magnetic effect (CME). We report measurements by the STAR collaboration of a CME-sensitive observable in p+Au and d+Au collisions at 200 GeV, where the CME is not expected, using charge-dependent pair correlations relative to a third particle. We observe strong charge-dependent correlations similar to those measured in heavy-ion collisions. This bears important implications for the interpretation of the heavy-ion data
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