5,901 research outputs found
Medium information from anisotropic flow and jet quenching in relativistic heavy ion collisions
Within a multiphase transport (AMPT) model, where the initial conditions are
obtained from the recently updated HIJING 2.0 model, the recent anisotropic
flow and suppression data for charged hadrons in Pb+Pb collisions at the LHC
center of mass energy of 2.76 TeV are explored to constrain the properties of
the partonic medium formed. In contrast to RHIC, the measured centrality
dependence of charged hadron multiplicity dN_ch/deta at LHC provides severe
constraint to the largely uncertain gluon shadowing parameter s_g. We find
final-state parton scatterings reduce considerably hadron yield at midrapidity
and enforces a smaller s_g to be consistent with dN_ch/deta data at LHC. With
the parton shadowing so constrained, hadron production and flow over a wide
transverse momenta range are investigated in AMPT. The model calculations for
the elliptic and triangular flow are found to be in excellent agreement with
the RHIC data, and predictions for the flow coefficients v_n(p_T, cent) at LHC
are given. The magnitude and pattern of suppression of the hadrons in AMPT are
found consistent with the measurements at RHIC. However, the suppression is
distinctly overpredicted in Pb+Pb collisions at the LHC energy. Reduction of
the QCD coupling constant alpha_s by ~30% in the higher temperature plasma
formed at LHC reproduces the measured hadron suppression.Comment: Talk given by Subrata Pal at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Silicon Pad Detectors for the PHOBOS Experiment at RHIC
The PHOBOS experiment is well positioned to obtain crucial information about
relativistic heavy ion collisions at RHIC, combining a multiplicity counter
with a multi-particle spectrometer. The multiplicity arrays will measure the
charged particle multiplicity over the full solid angle. The spectrometer will
be able to identify particles at mid-rapidity. The experiment is constructed
almost exclusively of silicon pad detectors. Detectors of nine different types
are configured in the multiplicity and vertex detector (22,000 channels) and
two multi-particle spectrometers (120,000 channels). The overall layout of the
experiment, testing of the silicon sensors and the performance of the detectors
during the engineering run at RHIC in 1999 are discussed.Comment: 7 pages, 7 figures, 1 table, Late
Is Strangeness still interesting at RHIC ?
With the advent of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven
National Laboratory (BNL), Heavy Ion Physics will enter a new energy regime.
The question is whether the signatures proposed for the discovery of a phase
transition from hadronic matter to a Quark Gluon Plasma (QGP), that were
established on the basis of collisions at the BEVALAC, the AGS, and the SPS,
respectively, are still useful and detectable at these high incident energies.
In the past two decades, measurements related to strangeness formation in the
collision were advocated as potential signatures and were tested in numerous
fixed target experiments at the AGS and the SPS. In this article I will review
the capabilities of the RHIC detectors to measure various aspects of
strangeness, and I will try to answer the question whether the information
content of those measurements is comparable to the one at lower energies.Comment: 12 pages, 7 figures, Invited Talk at the IV International Conference
on Strangeness in Quark Matter, Padova (Italy), July 20-24, 199
Quenching and Tomography from RHIC to LHC
We compare fully perturbative and fully nonperturbative pictures of high-pT
energy loss calculations to the first results from LHC. While over-suppressed
compared to published ALICE data, parameter-free pQCD predictions based on the
WHDG energy loss model constrained to RHIC data simultaneously describe well
the preliminary CMS hadron suppression, ATLAS charged hadron v2, and ALICE D
meson suppression; we also provide for future reference WHDG predictions for B
meson RAA. However, energy loss calculations based on AdS/CFT also
qualitatively describe well the RHIC pion and non-photonic electron suppression
and LHC charged hadron suppression. We propose the double ratio of charm to
bottom quark RAA will qualitatively distinguish between these two energy loss
pictures.Comment: 4 pages, 3 figures. Proceedings for Quark Matter 201
NLO analysis of inclusive jet, tagged jet and di-jet production in Pb+Pb collisions at the LHC
We present results and predictions at next-to-leading order for the recent
LHC lead-lead run at a center-of-mass energy of 2.76 TeV per nucleon-nucleon
pair. Specifically, we focus on the suppression the single and double inclusive
jet cross sections and demonstrate how the di-jet asymmetry, recently measured
by ATLAS and CMS, can be extracted from this general result. The case of jets
tagged by an electroweak boson is exemplified by the +jet channel. We
predict a signature transition from enhancement to suppression of the tagged
jet related to the medium-induced modification of the parton shower. Finally,
we clarify the relation between the suppression of inclusive jets, tagged jets
and di-jets and the quenching of inclusive particles on the example of the
recent ALICE charged hadron attenuation data.Comment: Version abridged to 4 pages to be published in J. Phys.
Report of the LHC Computing Grid Project. RTAG 12: Collaborative Tools
This document is the final report of the LHC Computing Grid (LCG) Project's Requirements and Technical Assessment Group (RTAG 12) on Collaborative Tools. It presents a summary of the requirements of the LHC collaborations for Collaborative Tools, assesses the current status of those tools in common use, discusses likely relevant future development, and provides recommendations for action by the LCG, the collaborations, and CERN for the immediate and long-term future. The requirements and assessments were assembled from formal and informal interactions between members of the RTAG, representatives of the LHC collaborations, CERN IT, and experts in the field of Collaborative Tools
Pseudorapidity and centrality dependence of the collective flow of charged particles in Au+Au collisions at sqrt{s_NN} = 130 GeV
This paper describes the measurement of collective flow for charged particles
in Au+Au collisions at sqrt{s_NN}} = 130 GeV using the PHOBOS detector at the
Relativistic Heavy Ion Collider (RHIC). An azimuthal anisotropy is observed in
the charged particle hit distribution in the PHOBOS multiplicity detector. This
anisotropy is presented over a wide range of pseudorapidity (eta) for the first
time at this energy. The size of the anisotropy (v_{2}) is thought to probe the
degree of equilibration achieved in these collisions. The result here,averaged
over momenta and particle species, is observed to reach 7% for peripheral
collisions at mid-rapidity, falling off with centrality and increasing |eta|.
Data are presented as a function of centrality for |eta|<1.0 and as a function
of eta, averaged over centrality, in the angular region -5.0<eta<5.3. These
results call into question the common assumption of longitudinal boost
invariance over a large region of rapidity in RHIC collisions.Comment: 5 pages, 4 figures, submitted to Physical Review Letter
Run 2 Upgrades to the CMS Level-1 Calorimeter Trigger
The CMS Level-1 calorimeter trigger is being upgraded in two stages to
maintain performance as the LHC increases pile-up and instantaneous luminosity
in its second run. In the first stage, improved algorithms including
event-by-event pile-up corrections are used. New algorithms for heavy ion
running have also been developed. In the second stage, higher granularity
inputs and a time-multiplexed approach allow for improved position and energy
resolution. Data processing in both stages of the upgrade is performed with
new, Xilinx Virtex-7 based AMC cards.Comment: 10 pages, 7 figure
Nucleon-Gold Collisions at 200 AGeV Using Tagged d+Au Interactions in PHOBOS
Forward calorimetry in the PHOBOS detector has been used to study charged
hadron production in d+Au, p+Au and n+Au collisions at sqrt(s_nn) = 200 GeV.
The forward proton calorimeter detectors are described and a procedure for
determining collision centrality with these detectors is detailed. The
deposition of energy by deuteron spectator nucleons in the forward calorimeters
is used to identify p+Au and n+Au collisions in the data. A weighted
combination of the yield of p+Au and n+Au is constructed to build a reference
for Au+Au collisions that better matches the isospin composition of the gold
nucleus. The p_T and centrality dependence of the yield of this improved
reference system is found to match that of d+Au. The shape of the charged
particle transverse momentum distribution is observed to extrapolate smoothly
from pbar+p to central d+Au as a function of the charged particle
pseudorapidity density. The asymmetry of positively- and negatively-charged
hadron production in p+Au is compared to that of n+Au. No significant asymmetry
is observed at mid-rapidity. These studies augment recent results from
experiments at the LHC and RHIC facilities to give a more complete description
of particle production in p+A and d+A collisions, essential for the
understanding the medium produced in high energy nucleus-nucleus collisions.Comment: 17 pages, 18 figure
Energy dependence of particle multiplicities in central Au+Au collisions
We present the first measurement of the pseudorapidity density of primary
charged particles in Au+Au collisions at sqrt(s_NN) = 200GeV. For the 6% most
central collisions, we obtain dN_ch/deta|_|eta|<1 = 650 +/- 35 (syst). Compared
to collisions at sqrt(s_NN) = 130GeV, the highest energy studied previously, an
increase by a factor of 1.14 +/- 0.05 is found. The energy dependence of the
pseudorapidity density is discussed in comparison with data from proton-induced
collisions and theoretical predictions.Comment: 4 pages, 6 figures, submitted to PR
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