2,706 research outputs found
Measurements of Lambda, Lambda-bar and K-short from Pb-Pb collisions at 158 GeV per nucleon in a large acceptance experiment
The main reason for studying relativistic heavy-ion collisions is to discover the phase transition from nuclear matter to the Quark-Gluon Plasma. Such a transition is predicted to occur under conditions of high temperature and density. The predicted state features deconfined quarks and gluons as the relevant degrees of freedom instead of colour-singlet hadrons. These new degrees of freedom should lead to an enhanced production of strange quarks which has directly observable consequences on the composition of the final state hadrons detected in such a collision. The NA49 experiment is able to measure hadronic production in central Pb+Pb collisions. It uses a Pb beam, of energy 158 GeV per nucleon, from the CERN SPS with a fixed Pb target. The experiment features four large tracking detectors which can measure the trajectories of charged particles. In this thesis the method of reconstructing neutral strange particles, Lambda, Lambda-bar and K-short from their charged decay products is described. The procedure for correcting the raw yields for losses due to the limited experimental acceptance and efficiency in reconstruction is explained. An estimate of some systematic errors is made. The resulting rapidity distributions, which span either side of mid-rapidity are peaked (with the possible exception of Lambda) and the transverse momentum spectra fit the Hagedorn distribution. The inverse slope parameters, T_Lambda = 274 ± 5 MeV, T_Lambda-bar = 279 ± 10 MeV and T_K = 238 ± 5 MeV are consistent with the picture of transverse flow observed in these collisions. These results are compared with other measurements
Azimuthal correlations of forward di-hadrons in d+Au collisions at RHIC in the Color Glass Condensate
We present a good description of recent experimental data on forward
di-hadron azimuthal correlations measured in deuteron-gold collisions at RHIC,
where monojet production has been observed. Our approach is based on the Color
Glass Condensate effective theory for the small-x degrees of freedom of the
nuclear wave function, including the use of non-linear evolution equations with
running QCD coupling. Our analysis provides further evidence for the presence
of saturation effects in RHIC data.Comment: 4 pages, 2 figures, version to appear in PR
Upsilon cross section in p+p collisions at STAR
The main focus of the heavy flavor program at RHIC is to investigate the
properties of the dense matter produced in heavy-ion collisions by studying its
effect on open heavy flavor and quarkonia production. This in turn requires a
detailed understanding of their production in elementary p+p collisions so that
the dense matter effects can be later unfolded. In this paper, we present the
first mid-rapidity cross section measurement of bottomonium at
GeV with the STAR experiment. We compare our results with perturbative QCD
calculations. A brief status on the study of charmonium in STAR is given.Comment: 4 pages, 4 figures. To appear in the proceedings of Quark Matter 2006
as a special issue of Journal of Physics G: Nuclear and Particle Physic
The first measurement of meson semi-leptonic decay contribution to non-photonic electrons at RHIC
We present the first measurement for the meson semi-leptonic decay
contribution to non-photonic electrons at RHIC using non-photonic electron
azimuthal correlations with charged hadrons in p+p collisions at GeV from STAR.Comment: 4 pages, 3 figures, Quark Matter 2006 Proceedings, to appear in J.
Phys.
Physics with Identified Particles at STAR
New physics results with identified particles at STAR are presented.
Measurements at low address bulk properties of the collision, while those
at high address jet energy loss in the bulk matter produced. Between
these extremes, measurements at intermediate address the interplay
between jets and the bulk. We highlight: measurements of fluctuations as
a new, sensitive probe of the initial conditions and the equation of state;
correlations involving multi-strange particles, along with ratios of identified
particles to test coalescence as a mechanism of particle production at
intermediate ; three particle azimuthal correlation to search for conical
emission; and the energy and particle-type dependence of hadron production at
high to study quark and gluon jet energy loss.Comment: 9 pages, 7 figures. To appear in the proceedings of the 19th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions
(Quark Matter 2006), Shanghai, China, November 14-20, 200
Selected results on Strong and Coulomb-induced correlations from the STAR experiment
Using recent high-statistics STAR data from Au+Au and Cu+Cu collisions at
full RHIC energy I discuss strong and Coulomb-induced final state interaction
effects on identical () and non-identical () particle
correlations. Analysis of correlations reveals the strong and
Coulomb-induced FSI effects allowing for the first time to estimate space
extension of and sources and average shift between them. Source
imaging technique providing clean separation of these effects from effects due
to the source function itself is applied to one-dimensional relative momentum
correlation function of identical pions. For low momentum pions and/or
non-central collisions large departure from a single-Gaussian shape is
observed
Anomalous centrality variation of minijet angular correlations in Au-Au collisions at 62 and 200 GeV from STAR
We have measured 2D autocorrelations for all charged hadrons in STAR with
0.15 GeV/c and 1 from Au+Au collisions at 62 and 200
GeV. The correlation structure is dominated by a peak centered at zero relative
opening angles on and which we hypothesize is caused by
minimum-bias jets (minijets). We observe a large excess of minijet correlations
in more-central Au-Au collisions relative to binary-collision scaling (more
correlated pairs than expected from surface emission or even volume emission).
We also observe a sudden increase of the minijet peak amplitude and
width relative to binary-collision scaling of scattered partons which occurs at
an energy-dependent centrality point. There is a possible scaling of the
transition point with transverse particle density.Comment: Quark Matter 2008 proceedings, submitted to Journal of Physics G. v2:
added STAR Collaboration to author lis
K* production in Cu+Cu and Au+Au collisions at sqrt(s_{NN}) = 62.4 GeV and 200 GeV in STAR
We report the measurements of spectra of up to intermediate
region in mid-rapidity through its hadronic decay channel using the STAR
detector in Au+Au and Cu+Cu collisions at = 62.4 GeV
and 200 GeV. Particle ratios such as and is used to
understand the rescattering and regeneration effect on production in
the hadronic medium. The measurement using a high statistics
Au+Au 200 GeV dataset and nuclear modification factor measurement supports the
quark coalescence model of particle production in the intermediate range.Comment: 5 page
Centrality dependence of the ratios and - a test of thermalization in Au+Au collisions at RHIC
We present the centrality dependence of the ratios and
measured in Au+Au collisions at GeV by the
STAR experiment at RHIC. The results are compared to measurements of other
identified particles and recombination model expectations in order to gain
insight into the partonic collectivity and possible thermalization of the
produced medium.Comment: 4 pages, 2 figures, Quark Matter 2006 conference proceeding
Recent results of the STAR high-energy polarized proton-proton program at RHIC at BNL
The STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at
Brookhaven National Laboratory (BNL) is carrying out a spin physics program
colliding transverse or longitudinal polarized proton beams at
GeV to gain a deeper insight into the spin structure and
dynamics of the proton. These studies provide fundamental tests of Quantum
Chromodynamics (QCD).
One of the main objectives of the STAR spin physics program is the
determination of the polarized gluon distribution function through a
measurement of the longitudinal double-spin asymmetry, , for various
processes. Recent results will be shown on the measurement of for
inclusive jet production, neutral pion production and charged pion production
at GeV. In addition to these measurements involving longitudinal
polarized proton beams, the STAR collaboration has performed several important
measurements employing transverse polarized proton beams. New results on the
measurement of the transverse single-spin asymmetry, , for forward
neutral pion production and the first measurement of for mid-rapidity
di-jet production will be discussed.Comment: 8 pages, 5 figures, Invited talk given at the 17th International Spin
Physics Symposium (SPIN 2006), October 2006, Kyoto, Japa
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