3,129 research outputs found
Pseudorapidity dependence of parton energy loss in relativistic heavy ion collisions
We analyze the recent data from the BRAHMS Collaboration on the
pseudorapidity dependence of nuclear modification factors in Au+Au collisions
at = 200 GeV by using the full three dimensional hydrodynamic
simulations for the density effects on parton energy loss. We first compute the
transverse spectra at and 2.2, and next take a ratio
, where is a nuclear
modification factor. It is shown that hydrodynamic components account for
at low and that quenched pQCD components lead
at high which are consistent with the data.
Strong suppression at is compatible with the parton energy loss in
the final state.Comment: 5 pages, 4 figures; one figure adde
Overview of Hard processes at RHIC: high-pt light hadron and charm production
An overview of the experimental results on high-pt light hadron production
and open charm production is presented. Data on particle production in
elementary collisions are compared to next-to-leading order perturbative QCD
calculations. Particle production in Au+Au collisions is then compared to this
baseline.Comment: 9 pages, 6 figures, Strange Quark Matter 200
Jet-Like Correlations between Forward and Mid-Rapidity
Mid-rapidity azimuthal correlations probe di-jets originating mainly from
gluon-gluon hard-scattering. Measurements of such correlations have revealed
significant (gluon-)jet modification in central Au+Au collisions. Azimuthal
correlations at forward rapidity with a mid-rapidity high-pt hadron, on the
other hand, are sensitive primarily to quark-gluon hard-scattering and may
probe quark-jet modification in nuclear medium. They may be also sensitive to
the Color Glass Condensate by separating d-side and Au-side in d+Au collisions.
We present the first results on correlations of charged hadrons at forward
rapidity in the STAR FTPCs (2.7 < |eta| < 3.9, pt < 2 GeV/c) with high-pt
charged hadrons at mid-rapidity from the main TPC (|eta| 3 GeV/c).
Preliminary results from pp, d+Au, and Au+Au collisions at 200 GeV are
compared. Implications of the results are discussed.Comment: 8 pages, 3 figures. Invited talk at Hard Probes 2006, Asilomar, C
Identified hadron production at high transverse momenta in p+p collisions at sqrt(NN) = 200 GeV in STAR
We report the transverse momentum (pT) distributions for identified charged
pions, protons and anti-protons using events triggered by high deposit energy
in the Barrel Electro-Magnetic Calorimeter (BEMC) from p + p collisions at psNN
= 200 GeV. The spectra are measured around mid-rapidity (|y|<0.5) over the
range of 3<pT<15 GeV/c with particle identification (PID) by the relativistic
ionization energy loss (rdE/dx) in the Time Projection Chamber (TPC) in the
Solenoidal Tracker at RHIC (STAR). The charged pion, proton and anti-proton
spectra at high pT are compared with published results from minimum bias
triggered events and the Next-Leading-Order perturbative quantum chromodynamic
(NLO pQCD) calculations (DSS, KKP and AKK 2008). In addition, we present the
particle ratios of pi-/pi+, pbar/p, p/pi+ and pbar/pi- in p + p collisions.Comment: 4 pages, 4 figures, Hot Quark 2008 proceedin
Elliptical Flow in Relativistic Ion Collisions at s^(1/2)= 200 A GeV
A consistent picture of the Au+Au and D+Au, s^1/2 = 200 A GeV measurements at
RHIC obtained with the PHENIX, STAR, PHOBOS and BRAHMS detectors including both
the rapidity and transverse momentum spectra was previously developed with the
simulation LUCIFER. The approach was modeled on the early production of a fluid
of pre-hadrons after the completion of an initial, phase of high energy
interactions. The formation of pre-hadrons is discussed here, in a perturbative
QCD approach as advocated by Kopeliovich, Nemchik and Schmidt. In the second
phase of LUCIFER, a considerably lower energy hadron-like cascade ensues. Since
the dominant collisions occurring in this latter phase are meson-meson in
character while the initial collisions are between baryons, i.e. both involve
hadron sized interaction cross-sections, there is good reason to suspect that
the observed elliptical flow will be produced naturally, and this is indeed
found to be the case.Comment: 7 pages, 6 figure
Correlations and fluctuations studied with ALICE
The measurement of particle correlations and event-by-event fluctuations of
physical observables allows to study a large variety of properties of the
matter produced in ultra relativistic heavy-ion collisions. We will present
results for two-particle correlations, mean transverse momentum fluctuations,
and net charge fluctuations in Pb-Pb collisions at 2.76 TeV.Comment: 7 pages, 5 figures, Proceedings submitted for the 28th Winter
Workshop on Nuclear Dynamics, Puerto Rico, April 7-14, 2012; corrected typo
Modeling the jet quenching, thermal resonance production and hydrodynamical flow in relativistic heavy ion collisions
The event topology in relativistic heavy ion collisions is determined by
various multi-particle production mechanisms. The simultaneous model treatment
of different collective nuclear effects at high energies (such as a hard
multi-parton fragmentation in hot QCD-matter, thermal resonance production,
hydrodynamical flows, etc.) is actual but rather complicated task. We discuss
the simulation of the above effects by means of Monte-Carlo model HYDJET++.Comment: Talk given at Workshop "Hot Quarks 2010" (La Londe Les Maures,
France, June 21-26, 2010); 4 pages including 2 figures as EPS-files; prepared
using LaTeX package for publication in Journal of Physics: Conference Serie
Suppression of High Transverse Momentum Spectra in Au+Au Collisions at RHIC
Au+Au, A GeV measurements at RHIC, obtained with the PHENIX,
STAR, PHOBOS and BRAHMS detectors, have all indicated a suppression of neutral
pion production, relative to an appropriately normalized NN level. For central
collisions and vanishing pseudo-rapidity these experiments exhibit suppression
in charged meson production, especially at medium to large transverse momenta.
In the PHENIX experiment similar behavior has been reported for
spectra.
In a recent work on the simpler D+Au interaction, to be considered perhaps as
a tune-up for Au+Au, we reported on a pre-hadronic cascade mechanism which
explains the mixed observation of moderately reduced suppression at
higher pseudo-rapidity as well as the Cronin enhancement at mid-rapidity. Here
we present the extension of this work to the more massive ion-ion collisions.
Our major thesis is that much of the suppression is generated in a late stage
cascade of colourless pre-hadrons produced after an initial short-lived
coloured phase. We present a pQCD argument to justify this approach and to
estimate the time duration of this initial phase. Of essential
importance is the brevity in time of the coloured phase existence relative to
that of the strongly interacting pre-hadron phase. The split into two phases is
of course not sharp in time, but adequate for treating the suppression of
moderate and high mesons.Comment: 19 pages, 10 figure
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