156 research outputs found
Two-particle azimuthal correlation in d+Au and p+p collision at sqrt{s_NN}=200 GeV in STAR
No full textThe goal of high--energy heavy--ion physics is the full characterization of the quark--gluon plasma (QGP), which is a phase of strongly interacting matter where quarks and gluons are no longer confined in the nucleons and can move freely over longer distances. Such a phase probably existed shortly after the Big Bang, and can be produced in laboratory by heavy--ion collisions at a sufficiently large energy density. This new phase of matter is distinctly different from usual hadronic matter. Several signatures have been proposed to probe the QGP. The focus of the present work is on jet production. Jets are collimated beams of particles emitted in the collision. The case in which one jet is associated with the emission of a single direct photon (--jet event) is of particular interest. Photons go through the medium without interacting. For momentum conservation, the energy of the photon is equal to the energy of the initial jet. On the other side, jet particles interact with the medium, losing energy. The energy loss is an important parameter to characterize the medium density. Due to the high multiplicity in heavy--ion collisions, it is difficult to identify the case of --jet production. There are many sources of photons, the most dominant of which is the decay of neutral mesons (mainly and ). Analyzing the simplest case, that is p+p collisions, gives a necessary baseline measurement for --jet correlation studies in Au+Au collisions. This work focuses on di--hadron correlation, seen as a background study for --jet correlation. The properties of jets in p+p and d+Au collisions are analyzed. In this way, di--jet events are completely characterized, providing a reference frame for the study of --jet events. In the present analysis p+p and d+Au data, collected at the STAR experiment, have been studied. The detectors mainly used are the Barrel Electromagnetic Calorimeter (BEMC) and the Time Projection Chamber (TPC). The BEMC is a lead--scintillator sampling calorimeter located at mid--rapidity ($|\eta| has been evaluated as a function of jet particles momentum. It is possible to study the relations between the two jets of a di--jet event from the parameters describing a single jet shape. The di--jet acoplanarity is measured with an azimuthal particle correlation approach. In this thesis the results for and have been extended to higher associated particle pT compared to previous measurements from other experiments, results obtained with charged hadrons and full jet reconstruction. In the overlap region the present results agree with all the previous ones
Jet properties from two-particle azimuthal correlations in d+Au collisions at VsNN = 200 GeV at STAR
No full textWe present measurements of azimuthal correlations between photons (from π0 decay) and charged hadrons in d+Au collisions at VsNN =200 GeV. We use di-hadron correlations to study parton fragmentation in d+Au collisions at RHIC. Specifically, the near-side and away-side peaks of the azimuthal angular difference distribution are used to measure the root-mean-squared (RMS) fragmentation transverse momentum and the mean intrinsic parton transverse momentum . The measurements with leading photons are compared to results using leading charged particles
Parton energy loss in heavy-ion collisions via direct-photon and charged-particle Azimuthal Correlations
No full textCharged-particle spectra associated with direct photon (γdir ) and π0 are measured in p+p and Au+Au collisions at center-of-mass energy √sNN=200 GeV with the STAR detector at RHIC. A hower-shape analysis is used to partially discriminate between γdir and π0. Assuming no associated charged particles in the γdir direction (near side) and small contribution from fragmentation photons (γfrag), the associated charged-particle yields opposite to γdir (away side) are extracted. At mid-rapidity (|η
Jet properties from two-particle azimuthal correlations in d+Au collisions at =200 GeV at STAR
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Neutral pion production in Au+Au collisions at [v]sNN=200 GeV
No full textThe results of midrapidity (
K/π fluctuations at relativistic energies
No full textWe report K/π fluctuations from Au+Au collisions at √sNN=19.6, 62.4, 130, and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. K/π fluctuations in central collisions show little dependence on incident energy and are on the same order as those from NA49 at the Super Proton Synchrotron in central Pb+Pb collisions at √sNN=12.3 and 17.3 GeV. We report results for the collision centrality dependence of K/π fluctuations and results for charge-separated fluctuations. We observe that the K/π fluctuations scale with the charged particle multiplicity density
Observation of pi+ pi- pi+ pi- photoproduction in ultra-peripheral heavy ion collisions at sqrt(s)NN=200 GeV at the STAR detector
No full textWe present a measurement of π+π-π+π- photonuclear production in ultraperipheral Au-Au collisions at √sNN=200 GeV from the STAR experiment. The π+π-π+π- final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The π+π-π+π- invariant mass spectrum of the coherent events exhibits a broad peak around 1540±40 MeV/c2 with a width of 570±60 MeV/c2, in agreement with the photoproduction data for the ρ0(1700). We do not observe a corresponding peak in the π+π- final state and measure an upper limit for the ratio of the branching fractions of the ρ0(1700) to π+π- and π+π-π+π- of 2.5% at 90% confidence level. The ratio of ρ0(1700) and ρ0(770) coherent production cross sections is measured to be 13.4±0.8stat.±4.4syst.%
Identified particle production, azimuthal anisotropy, and interferometry measurements in Au+Au collisions at sqrt(s)NN = 9.2 GeV
No full textWe present the first measurements of identified hadron production, azimuthal anisotropy, and pion interferometry from Au+Au collisions below the nominal injection energy at the BNL Relativistic Heavy-Ion Collider (RHIC) facility. The data were collected using the large acceptance solenoidal tracker at RHIC (STAR) detector at √sNN=9.2 GeV from a test run of the collider in the year 2008. Midrapidity results on multiplicity density dN/dy in rapidity y, average transverse momentum 〈pT〉, particle ratios, elliptic flow, and Hanbury-Brown–Twiss (HBT) radii are consistent with the corresponding results at similar √sNN from fixed-target experiments. Directed flow measurements are presented for both midrapidity and forward-rapidity regions. Furthermore the collision centrality dependence of identified particle dN/dy, 〈pT〉, and particle ratios are discussed. These results also demonstrate that the capabilities of the STAR detector, although optimized for √sNN=200 GeV, are suitable for the proposed QCD critical-point search and exploration of the QCD phase diagram at RHI
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