The inclusive J/ψ transverse momentum spectra and nuclear modification factors are reported at mid-rapidity (|y|<1.0) in Au + Au collisions at √sNN = 39, 62.4 and 200 GeV taken by the STAR ...experiment. A suppression of J/ψ production, with respect to the production in p+p scaled by the number of binary nucleon–nucleon collisions, is observed in central Au + Au collisions at these three energies. No significant energy dependence of nuclear modification factors is found within uncertainties. The measured nuclear modification factors can be described by model calculations that take into account both suppression of direct J/ψ production due to the color screening effect and J/ψ regeneration from recombination of uncorrelated charm–anticharm quark pairs.
Human quinolinate phosphoribosyltransferase (EC 2.4.2.19) (hQPRTase) is a member of the type II phosphoribosyltransferase family involved in the catabolism of quinolinic acid (QA). It catalyses the ...formation of nicotinic acid mononucleotide from quinolinic acid, which involves a phosphoribosyl transfer reaction followed by decarboxylation. hQPRTase has been implicated in a number of neurological conditions and in order to study it further, we have carried out structural and kinetic studies on recombinant hQPRTase. The structure of the fully active enzyme overexpressed in Escherichia coli was solved using multiwavelength methods to a resolution of 2.0 Å. hQPRTase has a α/β barrel fold sharing a similar overall structure with the bacterial QPRTases. The active site of hQPRTase is located at an α/β open sandwich structure that serves as a cup for the α/β barrel of the adjacent subunit with a QA binding site consisting of three arginine residues (R102, R138 and R161) and two lysine residues (K139 and K171). Mutation of these residues affected substrate binding or abolished the enzymatic activity. The kinetics of the human enzyme are different to the bacterial enzymes studied, hQPRTase is inhibited competitively and non-competitively by one of its substrates, 5-phosphoribosylpyrophosphate (PRPP). The human enzyme adopts a hexameric arrangement, which places the active sites in close proximity to each other.
High transverse momentum ( ) particle production is suppressed owing to the parton (jet) energy loss in the hot dense medium created in relativistic heavy-ion collisions. Redistribution of energy at ...low-to-modest has been difficult to measure, owing to large anisotropic backgrounds. We report a data-driven method for background evaluation and subtraction, exploiting the away-side pseudorapidity gaps, to measure the jetlike correlation shape in Au+Au collisions at GeV in the STAR experiment. The correlation shapes, for trigger particles and various associated particle ranges within , are consistent with Gaussians, and their widths increase with centrality. The results indicate jet broadening in the medium created in central heavy-ion collisions.
Abstract
High transverse momentum (
) particle production is suppressed owing to the parton (jet) energy loss in the hot dense medium created in relativistic heavy-ion collisions. Redistribution of ...energy at low-to-modest
has been difficult to measure, owing to large anisotropic backgrounds. We report a data-driven method for background evaluation and subtraction, exploiting the away-side pseudorapidity gaps, to measure the jetlike correlation shape in Au+Au collisions at
GeV in the STAR experiment. The correlation shapes, for trigger particles
and various associated particle
ranges within
, are consistent with Gaussians, and their widths increase with centrality. The results indicate jet broadening in the medium created in central heavy-ion collisions.
We report the STAR measurements of dielectron (e(+)e(-)) production at midrapidity (|y(ee)|<1) in Au+Au collisions at √s(NN)=200 GeV. The measurements are evaluated in different invariant mass ...regions with a focus on 0.30-0.76 (ρ-like), 0.76-0.80 (ω-like), and 0.98-1.05 (ϕ-like) GeV/c(2). The spectrum in the ω-like and ϕ-like regions can be well described by the hadronic cocktail simulation. In the ρ-like region, however, the vacuum ρ spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of 1.77±0.11(stat)±0.24(syst)±0.33(cocktail) is determined with respect to the hadronic cocktail simulation that excludes the ρ meson. The excess yield in the ρ-like region increases with the number of collision participants faster than the ω and ϕ yields. Theoretical models with broadened ρ contributions through interactions with constituents in the hot QCD medium provide a consistent description of the dilepton mass spectra for the measurement presented here and the earlier data at the Super Proton Synchrotron energies.
We report a case of bacteremia due to Abiotrophia species in a patient with neutropenic fever and cancer who was receiving levofloxacin prophylaxis, followed by empirical therapy with cefepime; the ...organism was resistant to both antibiotics. We provide susceptibility data on 20 additional bloodstream isolates of Abiotrophia species.
We report the first measurement of the elliptic anisotropy (v2) of the charm meson D0 at midrapidity (|y| < 1) in Au+Au collisions at sNN=200 GeV. The measurement was conducted by the STAR experiment ...at RHIC utilizing a new high-resolution silicon tracker. The measured D0 v2 in 0%-80% centrality Au+Au collisions can be described by a viscous hydrodynamic calculation for a transverse momentum (pT) of less than 4 GeV/c. The D0 v2 as a function of transverse kinetic energy (mT-m0, where mT=pT2+m02) is consistent with that of light mesons in 10%-40% centrality Au+Au collisions. These results suggest that charm quarks have achieved local thermal equilibrium with the medium created in such collisions. Several theoretical models, with the temperature-dependent, dimensionless charm spatial diffusion coefficient (2πTDs) in the range of ~2-12, are able to simultaneously reproduce our D0 v2 result and our previously published results for the D0 nuclear modification factor.
Azimuthal angular correlations of charged hadrons with respect to the axis of a reconstructed (trigger) jet in Au+Au and p+p collisions at √s(NN)=200 GeV in STAR are presented. The trigger jet ...population in Au+Au collisions is biased toward jets that have not interacted with the medium, allowing easier matching of jet energies between Au+Au and p+p collisions while enhancing medium effects on the recoil jet. The associated hadron yield of the recoil jet is significantly suppressed at high transverse momentum (pTassoc) and enhanced at low pTassoc in 0%-20% central Au+Au collisions compared to p+p collisions, which is indicative of medium-induced parton energy loss in ultrarelativistic heavy-ion collisions.
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