624 research outputs found
Energy deposition in hard dihadron triggered events in heavy-ion collisions
The experimental observation of hadrons correlated back-to-back with a
(semi-)hard trigger in heavy ion collisions has revealed a splitting of the
away side correlation structure in a low to intermediate transverse momentum
(P_T) regime. This is consistent with the assumption that energy deposited by
the away side parton into the bulk medium produced in the collision excites a
sonic shockwave (a Mach cone) which leads to away side correlation strength at
large angles. A prediction following from assuming such a hydrodynamical origin
of the correlation structure is that there is a sizeable elongation of the
shockwave in rapidity due to the longitudinal expansion of the bulk medium.
Using a single hadron trigger, this cannot be observed due to the unconstrained
rapidity of the away side parton. Using a dihadron trigger, the rapidity of the
away side parton can be substantially constrained and the longitudinal
structure of the away side correlation becomes accessible. However, in such
events several effects occur which change the correlation structure
substantially: There is not only a sizeable contribution due to the
fragmentation of the emerging away side parton, but also a systematic bias
towards small energy deposition into the medium and hence a weak shockwave. In
this paper, both effects are addressed.Comment: 5 pages, 2 figure
Understanding jet quenching and medium response with di-hadron correlation
A brief review of the dependence of the dihadron correlations from RHIC
is presented. We attempt to construct a consistent picture that can describe
the data as a whole, focusing on the following important aspects, 1) the
relation between jet fragmentation of survived jet and medium response to
quenched jets, 2) the possible origin of the medium response and its relation
to intermediate physics for single hadron production, 3) the connection
between the near-side ridge and away-side cone, 4) and their relations to low
energy results.Comment: 8 pages, 8 figures, presented at the 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 2008. Updated with the published versio
meson production and partonic collectivity at RHIC
New results on -meson production and elliptic flow measurements
from RHIC 2004 run (Run-IV) have been reviewed. In addition, the di-hadron
correlation function between the trigged and and the associated
soft particles was simulated. Knowledge about these results are discussed.Comment: 8 pages, 7 figures; Invited talk in International Conference on
Strangess in Quark Matter (SQM2006), UCLA, California, USA, March 26-31,
2006; to be publsihed in the Proceeding isuue of J. Phys.
Syntaxin 1 Ser14 phosphorylation is required for nonvesicular dopamine release
Amphetamine (AMPH) is a psychostimulant that is commonly abused. The stimulant properties of AMPH are associated with its ability to increase dopamine (DA) neurotransmission. This increase is promoted by nonvesicular DA release mediated by reversal of DA transporter (DAT) function. Syntaxin 1 (Stx1) is a SNARE protein that is phosphorylated at Ser(14) by casein kinase II. We show that Stx1 phosphorylation is critical for AMPH-induced nonvesicular DA release and, in Drosophila melanogaster, regulates the expression of AMPH-induced preference and sexual motivation. Our molecular dynamics simulations of the DAT/Stx1 complex demonstrate that phosphorylation of these proteins is pivotal for DAT to dwell in a DA releasing state. This state is characterized by the breakdown of two key salt bridges within the DAT intracellular gate, causing the opening and hydration of the DAT intracellular vestibule, allowing DA to bind from the cytosol, a mechanism that we hypothesize underlies nonvesicular DA release
Pion interferometry in Au+Au collisions at = 200 GeV
We present a systematic analysis of two-pion interferometry in Au+Au
collisions at = 200 GeV using the STAR detector at RHIC. We
extract the HBT radii and study their multiplicity, transverse momentum, and
azimuthal angle dependence. The Gaussianess of the correlation function is
studied. Estimates of the geometrical and dynamical structure of the freeze-out
source are extracted by fits with blast wave parameterizations. The expansion
of the source and its relation with the initial energy density distribution is
studied.Comment: 21 pages, 30 figures. As published in Physics Review
Production of Pairs Accompanied by Nuclear Dissociation in Ultra-Peripheral Heavy Ion Collision
We present the first data on pair production accompanied by nuclear
breakup in ultra-peripheral gold-gold collisions at a center of mass energy of
200 GeV per nucleon pair. The nuclear breakup requirement selects events at
small impact parameters, where higher-order corrections to the pair production
cross section should be enhanced. We compare the pair kinematic distributions
with two calculations: one based on the equivalent photon approximation, and
the other using lowest-order quantum electrodynamics (QED); the latter includes
the photon virtuality. The cross section, pair mass, rapidity and angular
distributions are in good agreement with both calculations. The pair transverse
momentum, , spectrum agrees with the QED calculation, but not with the
equivalent photon approach. We set limits on higher-order contributions to the
cross section. The and spectra are similar, with no evidence
for interference effects due to higher-order diagrams.Comment: 6 pages with 3 figures Slightly modified version that will appear in
Phys. Rev.
Pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV
We present a systematic analysis of two-pion interferometry in Au+Au collisions at sqrt[sNN]=200GeV using the STAR detector at Relativistic Heavy Ion Collider. We extract the Hanbury-Brown and Twiss radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianness of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast-wave parametrizations. The expansion of the source and its relation with the initial energy density distribution is studied
Multiplicity and Pseudorapidity Distributions of Charged Particles and Photons at Forward Pseudorapidity in Au + Au Collisions at sqrt{s_NN} = 62.4 GeV
We present the centrality dependent measurement of multiplicity and
pseudorapidity distributions of charged particles and photons in Au + Au
collisions at sqrt{s_NN} = 62.4 GeV. The charged particles and photons are
measured in the pseudorapidity region 2.9 < eta < 3.9 and 2.3 < eta < 3.7,
respectively. We have studied the scaling of particle production with the
number of participating nucleons and the number of binary collisions. The
photon and charged particle production in the measured pseudorapidity range has
been shown to be consistent with energy independent limiting fragmentation
behavior. The photons are observed to follow a centrality independent limiting
fragmentation behavior while for the charged particles it is centrality
dependent. We have carried out a comparative study of the pseudorapidity
distributions of positively charged hadrons, negatively charged hadrons,
photons, pions, net protons in nucleus--nucleus collisions and pseudorapidity
distributions from p+p collisions. From these comparisons we conclude that
baryons in the inclusive charged particle distribution are responsible for the
observed centrality dependence of limiting fragmentation. The mesons are found
to follow an energy independent behavior of limiting fragmentation while the
behavior of baryons seems to be energy dependent.Comment: 17 pages and 20 figure
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