共查询到20条相似文献,搜索用时 31 毫秒
1.
A. G. Knospe 《The European Physical Journal C - Particles and Fields》2009,62(1):223-227
Heavy-flavor semileptonic decays are expected to dominate the spectrum of non-photonic electrons produced from collisions
at the energies of the Relativistic Heavy Ion Collider. The non-photonic electron yield is suppressed by approximately a factor
of 5 in central Au + Au events at
GeV relative to p+p events with the same collision energy. Most theoretical models predict less non-photonic-electron suppression than is observed
experimentally. We present a preliminary measurement of the yield of non-photonic electrons in Cu + Cu events at
GeV, as well as the nuclear modification factor. 相似文献
2.
P. Romatschke 《The European Physical Journal C - Particles and Fields》2007,52(1):203-209
Causal viscous hydrodynamic fits to experimental data for pion and kaon transverse momentum spectra from central Au + Au collisions
at are presented. Starting the hydrodynamic evolution at 1 fm/c and using small values for the relaxation time, reasonable fits up to moderate ratios, η/s≃0.4, can be obtained. It is found
that a percentage of roughly 50 η/s to 75 η/s of the final meson multiplicity is due to viscous entropy production. Finally,
it is shown that with increasing viscosity, the ratio of HBT radii Rout/Rside approaches and eventually matches the experimental data. 相似文献
3.
H. Buesching The PHENIX Collaboration 《The European Physical Journal C - Particles and Fields》2007,49(1):41-45
Over the first five years of operation the PHENIX experiment at RHIC has collected a wealth of data for various systems and
collision energies that is providing valuable information for the understanding of the suppression pattern observed in central
Au+Au collisions at . An overview on transverse-momentum (pT) spectra of π0 and η in different collision energies and systems is presented. 相似文献
4.
M. van Leeuwen 《The European Physical Journal C - Particles and Fields》2009,61(4):569-574
We present selected recent results of multi-hadron correlation measurements in azimuth and pseudorapidity at intermediate
and high p
T
in Au+Au collisions at
, from the STAR experiment at RHIC. At intermediate p
T
, measurements are presented that attempt to determine the origin of the associated near-side (small Δφ) yield at large pseudo-rapidity difference Δη that is found to be present in heavy ion collisions. In addition, results are reported on new multi-hadron correlation measures
at high-p
T
that use di-hadron triggers and multi-hadron cluster triggers with the goal to constrain the underlying jet kinematics better
than in the existing measurements of inclusive spectra and di-hadron correlations. 相似文献
5.
A. Marín 《The European Physical Journal C - Particles and Fields》2009,61(4):735-740
Heavy-ion collisions will enter a new era with the start of the CERN Large Hadron Collider (LHC). A first short run with proton-proton
collisions at the injection energy of 0.9 TeV will be followed by a longer one with pp collisions at 10 TeV. First Pb-Pb collisions at
TeV will take place in 2009. Three experiments (ALICE, ATLAS, and CMS) will study both pp and Pb-Pb collisions. A selection of results showing the capabilities of the three experiments for the study of the LHC medium
with direct photons is presented. 相似文献
6.
Hiroshi Masui 《The European Physical Journal C - Particles and Fields》2009,62(1):169-173
One of the most striking results is the large elliptic flow (v
2) at RHIC. Detailed mass and transverse momentum dependence of elliptic flow are well described by ideal hydrodynamic calculations
for p
T<1 GeV/c, and by parton coalescence/recombination picture for p
T=2–6 GeV/c. The systematic error on v
2 is dominated by so-called “non-flow effects”, which are correlations other than flow, such as resonance decays and jets.
It is crucial to understand and reduce the systematic error from non-flow effects in order to understand the underlying collision
dynamics. In this paper, we present the centrality dependence of v
2 with respect to the first harmonic event plane at ZDC-SMD (v
2{ZDC-SMD}) in Au + Au collisions at
GeV. A large rapidity gap (|Δη|>6) between midrapidity and the ZDC-SMD could enable us to minimize possible non-flow contributions. We compare the results
of v
2{ZDC-SMD} with v
2{BBC}, which is measured by event plane determined at |η|=3.1–3.9. Possible non-flow contributions in those results will be discussed. 相似文献
7.
Results from RHIC have shown that there is an enhanced baryon/meson ratio in the intermediate transverse momentum range (2<pT<6 GeV/c) in Au+Au collisions at both =130 and 200 GeV. This was initially demonstrated by measurements of the p̄/π- ratio which was then extended in pT by the Λ/K0
S ratio. The data were successfully described by models utilising different hadronization mechanisms: those having recombination
of quarks and others having an interplay between flow, jet quenching and incorporating baryon junction loops. The strange
particle data from the first Au+Au run at =200 GeV gave tantalising hints that the observed enhancement of baryons compared to mesons was diminished by a pT of 6 GeV/c, but a lack of statistics in this range made a definitive statement impossible. Here we present an extended analysis
of identified strange baryons and mesons in Au+Au collisions at =200 GeV using data obtained by the STAR experiment from the 2004 running period. The increase in statistics extends the
measurement of Λ hyperons out to at least 7 GeV/c and K0
S mesons out to 9 GeV/c. This data allows us to place limits on the range where in-vacuum fragmentation functions are applicable
and the effect of baryon dominance is reduced. We also discuss the prospects for making these measurements using multiply-strange
baryons and mesons (Ω and ϕ). 相似文献
8.
A. Toia 《The European Physical Journal C - Particles and Fields》2007,49(1):243-247
The first measurement of the dielectron continuum at RHIC energies was performed by the PHENIX experiment for Au+Au collisions
at =200 GeV. Mass spectra for different centralities are presented and compared with the expectations from hadron decays. 相似文献
9.
D. Molnar 《The European Physical Journal C - Particles and Fields》2007,49(1):181-186
There are several indications that an opaque partonic medium is created in energetic Au+Au collisions at the relativistic heavy ion collider (RHIC). At the extreme densities of ∼10–100 times normal nuclear density reached,
even heavy-flavor hadrons are affected significantly. Heavy-quark observables are presented from the parton transport model
MPC, focusing on the nuclear suppression pattern, azimuthal anisotropy (“elliptic flow”), and azimuthal correlations. Comparison
with Au+Au data at top RHIC energy indicates significant heavy-quark rescattering, corresponding roughly five times higher opacities than estimates based on
leading-order perturbative QCD. We propose measurements of charm–anticharm, e.g., D-meson azimuthal correlations as a sensitive,
independent probe to corroborate these findings.
PACS 25.75.-q; 25.75.Ld; 25.75.Gz 相似文献
10.
L. Gaillard 《The European Physical Journal C - Particles and Fields》2007,49(1):51-55
Here we present initial studies of two-dimensional angular correlations of Λ, Λ̄, and K0
Short triggers with unidentified charged hadrons in Au+Au collisions at =200 GeV measured by STAR. Distributions of pseudo-rapidity difference, Δη, and azimuthal separation, Δφ, are constructed
containing structures observed in unidentified hadron correlations, including a jet peak at small Δη-Δφ accompanied by a flow-like
ridge extended over Δη. These features are studied as a function of centrality via integrated yields and fitting to projections
onto Δη and Δφ axes. Yields are found to be consistent with unidentified correlation analyses, and no clear distinction is
observed between the three species.
PACS 25.75.Gz 相似文献
11.
Camelia Mironov Ramona Vogt Gerd J. Kunde 《The European Physical Journal C - Particles and Fields》2009,61(4):893-898
We propose a new method for identifying and isolating
events through semileptonic decays of the
pair. Employing these decay dileptons to tag the jet in a specific kinematic region provides a clean signature of jets associated
with heavy-quark production. The measurement, in both pp and heavy-ion collisions, is essential for addressing heavy-quark fragmentation in vacuum and in a dense medium. We present
next-to-leading order calculations of
production (leading order in
production) in
TeV pp collisions at the LHC and discuss the feasibility of the measurement in heavy-ion collisions at
TeV. 相似文献
12.
F. Benedosso 《The European Physical Journal C - Particles and Fields》2007,49(1):61-64
We present measurements of azimuthal correlations between photons (from π0 decay) and charged hadrons in d+Au collisions at =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.
PACS 25.75.-q 相似文献
13.
D.J. Kim 《The European Physical Journal C - Particles and Fields》2007,49(1):359-364
The PHENIX experiment has studied open heavy flavor production in =200 GeV p+p and d+Au collisions using the semi-leptonic decay into single muons. The results from these measurements and
the details of the analysis technique are presented. The results from p+p collisions obtained at mid-rapidity are compared
to perturbative QCD calculations. The production of light mesons is the major background source for the open flavor measurement
using muons. The nuclear modification factor for light mesons were measured in Cu+Cu collisions at =200 GeV is presented. 相似文献
14.
Anthony R. Timmins 《The European Physical Journal C - Particles and Fields》2009,62(1):249-254
We report STAR measurements of mid-rapidity yields for the Λ ,
, K
S
0 , Ξ
−,
, Ω
−,
particles in Cu + Cu and Au + Au
GeV collisions. We show that at a given number of participating nucleons, bulk strangeness production is higher in Cu + Cu
collisions compared to Au + Au collisions at the same center of mass energy, counter to predictions from the Canonical formalism.
We compare both the Cu + Cu and Au + Au yields to AMPT and EPOS predictions, and find they reproduce key qualitative aspects
of the data. Finally, we investigate other scaling parameters and find bulk strangeness production for both the measured data
and theoretical predictions, scales better with the number participants that undergo more than one collision. 相似文献
15.
H. Rauch 《The European physical journal. Special topics》2008,159(1):27-36
Measurements of the π0 and direct photon nuclear modification
factors in p+p and A+A collisions in the PHENIX experiment
at RHIC will be reviewed and
recent results at
GeV will be presented. Using
for the first time the p+p reference measured in the same
experiment instead of averaging world data the π0 suppression
turns out to be almost as large at
GeV as at
GeV, implying gluon densities dNg/dy>800.
Possible origins of photon suppression at high pT in
GeV are discussed in light of the new results on
photon RAA at
GeV. 相似文献
16.
A. Capella L. Bravina E. G. Ferreiro A. B. Kaidalov K. Tywoniuk E. Zabrodin 《The European Physical Journal C - Particles and Fields》2008,58(3):437-444
Charmonium production at heavy-ion colliders is considered within the comovers-interaction model. The formalism is extended
by including possible secondary J/ψ production through recombination and an estimate of recombination effects is made without adjusting the model parameters.
The comovers-interaction model also includes a comprehensive treatment of initial-state nuclear effects, which are discussed
in the context of such high energies. With these tools, the model properly describes the centrality and the rapidity dependence
of experimental data at RHIC energy,
GeV, for both Au+Au and Cu+Cu collisions. Predictions for LHC,
TeV, are presented and the assumptions and extrapolations involved are discussed. 相似文献
17.
Sevil Salur 《The European Physical Journal C - Particles and Fields》2009,62(1):119-125
Jets can be used to probe the physical properties of the high energy density matter created in collisions at the Relativistic
Heavy Ion Collider (RHIC). Measurements of strong suppression of inclusive hadron distributions and di-hadron correlations
at high p
T
have already provided evidence for partonic energy loss. However, these measurements suffer from well-known geometric biases
due to the competition of energy loss and fragmentation. These biases can be avoided if the jets are reconstructed independently
of their fragmentation details—quenched or unquenched. In this paper, we discuss modern jet reconstruction algorithms (cone
and sequential recombination) and their corresponding background subtraction techniques required by the high multiplicities
of heavy ion collisions. We review recent results from the STAR experiment at RHIC on direct jet reconstruction in central
Au+Au collisions at
GeV. 相似文献
18.
A. K. Chaudhuri 《The European Physical Journal C - Particles and Fields》2009,61(2):331-338
In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy,
GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T
J/ψ
. Sequential melting of charmonium states (χ
c
, ψ
′ and J/ψ), with melting temperatures
, T
J/ψ
≈2T
c
and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ
p
T
spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts
the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ
p
T
spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,
GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ
p
T
distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC. 相似文献
19.
Sevil Salur 《The European Physical Journal C - Particles and Fields》2009,61(4):761-767
We present the first measurement of reconstructed jets in ultra-relativistic heavy ion collisions. Utilizing the large coverage
of the STAR Time Projection Chamber and Electromagnetic Calorimeter, we apply several modern jet reconstruction algorithms
and background subtraction techniques and explore their systematic uncertainties in heavy ion events. The differential energy
spectrum for inclusive jet production in central Au+Au collisions at
is presented. In order to assess the jet reconstruction biases, this spectrum is compared with the jet cross section measured
in
GeV p+p collisions scaled by the number of binary N–N collisions to account for nuclear geometric effects. 相似文献
20.
Yichun Xu 《The European Physical Journal C - Particles and Fields》2009,62(1):187-190
We report the transverse momentum (p
T
) 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
GeV. The spectra are measured around mid-rapidity (|y|<0.5) over the range of 3<p
T
<15 GeV/c with particle identification (PID) by the relativistic ionization energy loss (rdE/dx) in the Time Projection Chamber (TPC) of the Solenoidal Tracker at RHIC (STAR). The charged pion, proton and anti-proton
spectra at high p
T
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 π
−/π
+,
, p/π
+ and
in p+p collisions. 相似文献