941 research outputs found
Jet Studies in STAR via 2+1 Correlations
This paper reports analysis on jet-medium interactions and di-jet surface
emission bias at RHIC, based on a new multi-hadron correlation technique called
\texttt{2+1} where back-to-back high hadron triggers work as proxy of
di-jets. In contrast with traditional correlations with single triggers, the
associated hadron distributions and spectra at both trigger sides show no
evident modification from d+Au to central Au+Au collisions. This observation
stands for both cases when triggers pairs are symmetric(5GeV/ vs.
4GeV/) or asymmetric(10GeV/ vs. 4GeV/).Comment: DIS 2011 conference proceeding
Event-plane-dependent dihadron correlations with harmonic vn subtraction in Au + Au collisions at âsNN=200 GeV
STAR measurements of dihadron azimuthal correlations (ÎÏ) are reported in midcentral (20â60%) Auâ+âAu collisions at âsNN=200 GeV as a function of the trigger particle's azimuthal angle relative to the event plane, Ïs=|ÏtâÏEP|. The elliptic (v2), triangular (v3), and quadratic (v4) flow harmonic backgrounds are subtracted using the zero yield at minimum (ZYAM) method. The results are compared to minimum-bias dâ+âAu collisions. It is found that a finite near-side (|ÎÏ|Ï/2) correlation shows a modification from dâ+âAu data, varying with Ïs. The modification may be a consequence of path-length-dependent jet quenching and may lead to a better understanding of high-density QCD
Enabling comparison of UrQMD with Geant4 hadronic models
Geant4 has an abundant set of physics models that handle the diverse
interaction of particles with matter across a wide energy range. However, there
are also many well established reaction codes currently used in the same fields
where Geant4 is applied. One such code is the Ultra-relativistic Quantum
Molecular Dynamics (UrQMD) model. In order to take advantage of the UrQMD code,
we create a tool to enable comparisons among UrQMD and Geant4 hadronic models.
This tool allows a user to process the output file of UrQMD through Geant4
toolkit, while at the same time, can choose among different Geant4 hadronic
model generators. As an example, the UrQMD model is compared with the HARP-CDP
experimental data and with the Binary and FRITIOF generators, in the framework
of Geant4. It is shown that the UrQMD model can better reproduce charged pion
production for p+Cu and Pb interactions at 3, 8 and 15 GeV/c, and is a good
candidate for Geant4 hadronic models.Comment: 17 pages, 5 Figure
Event Plane Dependent Dihadron Correlations with Harmonic Vâż Subtraction in Au + Au Collisions at âËąáŽșáŽș = 200 GeV
STAR measurements of dihadron azimuthal correlations (ÎΊ) are reported in midcentral (20-60%) Au + Au collisions at âËąáŽșáŽș = 200 GeV as a function of the trigger particle\u27s azimuthal angle relative to the event plane, Ίs = | Ίt- ΚEP|. The elliptic (v2), triangular (v3), and quadratic (v4) flow harmonic backgrounds are subtracted using the zero yield at minimum (ZYAM) method. It is found that a finite near-side (|ÎΊ| \u3c Ï/2) long-range pseudorapidity correlation (ridge) is present in the in-plane direction (Ίs ~ 0). The away-side (|ÎΊ| \u3e Ï/2) correlation shows a modification from d+ Au data, varying with Ίs. The modification may be a consequence of path-length-dependent jet quenching and may lead to a better understanding of high-density QCD
A versatile method for simulating pp -> ppe+e- and dp -> pne+e-p_spec reactions
We have developed a versatile software package for the simulation of
di-electron production in and collisions at SIS energies. Particular
attention has been paid to incorporate different descriptions of the Dalitz
decay via a common interface. In addition, suitable
parameterizations for the virtual bremsstrahlung process
based on one-boson exchange models have been implemented. Such simulation tools
with high flexibility of the framework are important for the interpretation of
the di-electron data taken with the HADES spectrometer and the design of
forthcoming experiments
What does the rho-meson do? In-medium mass shift scenarios versus hadronic model calculations
The NA60 experiment has studied low-mass muon pair production in In-In
collisions at with unprecedented precision. With these results
there is hope that the in-medium modifications of the vector meson spectral
function can be constrained more thoroughly than before. We investigate in
particular what can be learned about collisional broadening by a hot and dense
medium and what constrains the experimental results put on in-medium mass shift
scenarios. The data show a clear indication of considerable in-medium
broadening effects but disfavor mass shift scenarios where the -meson
mass scales with the square root of the chiral condensate. Scaling scenarios
which predict at finite density a dropping of the -meson mass that is
stronger than that of the quark condensate are clearly ruled out since they are
also accompanied by a sharpening of the spectral function.Comment: Proceeding contribution, Talk given by J. Ruppert at Workshop for
Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus
Collisions (Hot Quarks 2006), Villasimius, Sardinia, Italy, 15-20 May 2006.
To appear in EPJ
Chemical potential response of meson masses at finite temperature
We study the response of meson masses to the chemical potential
() at high temperature and at zero chemical
potential on lattice with staggered fermions. Preliminary results for
the meson composed of different quarks show that
is negative in the confinement phase and
positive in the deconfinement phase.Comment: Lattice 2000 (Finite Density), 4 pages, 2 figure
Pion damping width from SU(2) x SU(2) NJL model
Within the framework of the NJL model, we investigate the modification of the
pion damping width in a hot pion gas for temperatures ranging from 0 to 180
MeV. The pion is found to broaden noticeably at T > 60 MeV. Near the chiral
phase transition T ~ 180 MeV, the pion width is saturated and amounts to 70
MeV. The main contribution to the width comes from pion-pion collisions. Other
contributions are found negligibly small.Comment: LaTeX2e, 13 pages, 2 figure
Measurements of Dihadron Correlations Relative to the Event Plane in Au Plus Au Collisions at âSNN= 200 GeV
Dihadron azimuthal correlations containing a high transverse momentum (pT) trigger particle are sensitive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the traversing parton and the medium, i.e. jet-quenching. Previous measurements revealed a strong modification to dihadron azimuthal correlations in Au+Au collisions with respect to p+p and d+Au collisions. The modification increases with the collision centrality, suggesting a path-length or energy density dependence to the jet-quenching effect. This paper reports STAR measurements of dihadron azimuthal correlations in mid-central (20%-60%) Au+Au collisions at âsNN = 200 GeV as a function of the trigger particle\u27s azimuthal angle relative to the event plane, Ïs = |Ït - ÏEP| .The azimuthal correlation is studied as a function of both the trigger and associated particle pT. The subtractions of the combinatorial background and anisotropic flow, assuming Zero Yield At Minimum (ZYAM), are described. The correlation results are first discussed with subtraction of the even harmonic (elliptic and quadrangular) flow backgrounds. The away-side correlation is strongly modified, and the modification varies with Ïs, with a double-peak structure for out-of-plane trigger particles. The near-side ridge (long range pseudo-rapidity Îη correlation) appears to drop with increasing Ïs while the jet-like component remains approximately constant. The correlation functions are further studied with the subtraction of odd harmonic triangular flow background arising from fluctuations. It is found that the triangular flow, while responsible for the majority of the amplitudes, is not sufficient to explain the Ïs-dependence of the ridge or the away-side double-peak structure. The dropping ridge with Ïs, could be attributed to a Ïs-dependent elliptic anisotropy; however, the physics mechanism of the ridge remains an open question. Even with a Ïs-dependent elliptic flow, the away-side correlation structure is robust. These results, with extensive systematic studies of the dihadron correlations as a function of Ïs, trigger and associated particle pT, and the pseudo-rapidity range Îη, should provide stringent inputs to help understand the underlying physics mechanisms of jet-medium interactions in high energy nuclear collisions
Dilepton production by bremsstrahlung of meson fields in nuclear collisions
We study the bremsstrahlung of virtual omega mesons due to the collective
deceleration of nuclei at the initial stage of an ultrarelativistic heavy-ion
collision. It is shown that electromagnetic decays of these mesons may give an
important contribution to the observed yields of dileptons. Mass spectra of
positron-electron and muon pairs produced in central Au+Au collisions are
calculated under some simplifying assumptions on the space-time variation of
the baryonic current in a nuclear collision process. Comparison with the CERES
data for 160 AGev Pb+Au collisions shows that the proposed mechanism gives a
noticeable fraction of the observed lepton pairs in the intermediate region of
invariant masses. Sensitivity of the dilepton yield to the in-medium
modification of masses and widths of vector mesons is demonstrated.Comment: 14 page
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