Understanding the effects of cold nuclear matter on J/ψ production is a key requirement for interpreting the J/ψ suppression reported in heavy-ion collisions. Based on a Glauber model, the ...J/ψ–nucleon inelastic cross section is determined from a statistical analysis of the J/ψ world data on nuclear targets. The global fit of all data gives σ
J/ψN
= 3.4 ± 0.2 mb, significantly smaller than previous estimates, yet the χ
2
of the fit is pretty large, χ
2
/ndf=1.5. A similar value, σ
J/ψN
= 3.5 ± 0.2 ± 1.7 mb, is obtained when the De Florian–Sassot modifications of the nuclear parton densities are included in the analysis, although we emphasise that the present uncertainties on gluon (anti-) shadowing do not allow for a precise determination of σ
J/ψN
. Finally, the possible energy dependence of the J/ψ–nucleon inelastic cross section is investigated within this framework. No significant energy dependence of the J/ψ–N interaction is observed.
Objectives: To determine the prevalence of HIV and associated risk factors among female sex workers (FSWs) in border provinces of Vietnam. Methods: 911 FSWs in five border provinces of Vietnam (Lai ...Chau, Quang Tri, Dong Thap, An Giang, and Kien Giang) were enrolled in a cross sectional study. Subjects were interviewed using a standardised questionnaire about selected sociodemographic and behavioural characteristics, history of STIs, and information about their cohabiting partners (husbands or live-in partners). Serological tests were done for HIV and syphilis (TPHA+RPR) and urine tests (PCR) for chlamydia and gonorrhoea. Associations between HIV and selected features of FSWs and their partners were examined using univariate and multivariate logistic regression analysis. Results: Overall, the prevalence of HIV among FSWs in the five provinces of Vietnam was 4.5%. The prevalence of HIV was higher in the southern border regions (4.0%–7.0%) than the northern (2%) and central (1%) regions. In multivariate analysis between HIV and selected features of FSWs, income ⩽$33/month (OR 2.36, p = 0.04), age of first sex ⩽15 (OR = 5.48, p = 0.005), and ⩾9 clients per week (OR 2.80, p = 0.018) were associated with HIV infection. Positive syphilis serology achieved a borderline significant association with HIV (OR 2.30, p = 0.095). Having a regular non-paying partner (OR = 0.35, p = 0.060) was a borderline protective factor for HIV. Conclusion: Interventions to limit HIV transmission among FSWs in Vietnam should be implemented early and focus on young poor populations in these border areas.
Measurements of midrapidity charged-particle multiplicity distributions, dNch/dη, and midrapidity transverse-energy distributions, dET/dη, are presented for a variety of collision systems and ...energies. Included are distributions for Au+Au collisions at sNN=200, 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, Cu+Cu collisions at sNN=200 and 62.4 GeV, Cu+Au collisions at sNN=200 GeV, U+U collisions at sNN=193 GeV, d+Au collisions at sNN=200 GeV, He3+Au collisions at sNN=200 GeV, and p+p collisions at sNN=200 GeV. Centrality-dependent distributions at midrapidity are presented in terms of the number of nucleon participants, Npart, and the number of constituent quark participants, Nqp. For all A+A collisions down to sNN=7.7 GeV, it is observed that the midrapidity data are better described by scaling with Nqp than scaling with Npart. Also presented are estimates of the Bjorken energy density, BJ, and the ratio of dET/dη to dNch/dη, the latter of which is seen to be constant as a function of centrality for all systems.
In this paper, we present the first measurement of elliptic (v2) and triangular (v3) flow in high-multiplicity 3He+Aucollisions at √sNN=200 GeV. Two-particle correlations, where the particles have a ...large separation in pseudorapidity, are compared in 3He+Au and in p+p collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the 3He+Ausystem. The collective behavior is quantified in terms of elliptic v2 and triangular v3 anisotropy coefficients measured with respect to their corresponding event planes. The v2 values are comparable to those previously measured in d+Au collisions at the same nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three 3He nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. Finally, the agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.
The PHENIX collaboration presents first measurements of low-momentum (0.4<p_{T}<3 GeV/c) direct-photon yields from Au+Au collisions at sqrts_{NN}=39 and 62.4 GeV. For both beam energies the ...direct-photon yields are substantially enhanced with respect to expectations from prompt processes, similar to the yields observed in Au+Au collisions at sqrts_{NN}=200. Analyzing the photon yield as a function of the experimental observable dN_{ch}/dη reveals that the low-momentum (>1 GeV/c) direct-photon yield dN_{γ}^{dir}/dη is a smooth function of dN_{ch}/dη and can be well described as proportional to (dN_{ch}/dη)^{α} with α≈1.25. This scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and the Large Hadron Collider, for centrality selected samples, as well as for different A+A collision systems. At a given beam energy, the scaling also holds for high p_{T} (>5 GeV/c), but when results from different collision energies are compared, an additional sqrts_{NN}-dependent multiplicative factor is needed to describe the integrated-direct-photon yield.
PHENIX has measured the e(+)e(-) pair continuum in root s(NN) = 200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e(+)e(-) yield is compared to the expectations ...from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated c (c) over bar production, although other mechanisms are not ruled out. In the low-mass region, below the phi, the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7 +/- 0.4(stat) +/- 1.5(syst) +/- 0.9(model). At low mass (m(ee) < 0.3 GeV/c(2)) and high p(T) (1 < p(T) < 5 GeV/c) an enhanced e(+)e(-) pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in p(T), with inverse slope T = 221 +/- 19(stat) +/- 19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T-init similar or equal to 300-600 MeV at times of 0.6-0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low p(T) < 1 GeV/c the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of T similar or equal to 100 MeV. Theoretical models underpredict the low-mass, low-p(T) enhancement.
The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured electrons with 0.3 < p(T) < 9 GeV/c at midrapidity (y < 0.35) from heavy-flavor (charm and bottom) decays in Au + ...Au collisions at root s(NN) = 200 GeV. The nuclear modification factor R-AA relative to p + p collisions shows a strong suppression in central Au + Au collisions, indicating substantial energy loss of heavy quarks in the medium produced at RHIC energies. A large azimuthal anisotropy v(2) with respect to the reaction plane is observed for 0.5 < p(T) < 5 GeV/c indicating substantial heavy-flavor elliptic flow. Both R-AA and v(2) show a p(T) dependence different from those of neutral pions. A comparison to transport models which simultaneously describe R-AA(p(T)) and v(2)(p(T)) suggests that the viscosity to entropy density ratio is close to the conjectured quantum lower bound, i.e., near a perfect fluid.
In this paper, we report a measurement of e+e- pairs from semileptonic heavy-flavor decays in p + p collisions at √sNN = 200 GeV. The e+e- pair yield from $b\overline{b}$ and $c\overline{c}$ is ...separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and pT. We used three different event generators, pythia, mc@nlo, and powheg, to simulate the e+e- spectra from $c\overline{c}$ and $b\overline{b}$ production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to 4π, significant differences are observed for the total cross section. These difference are less pronounced for $b\overline{b}$ than for $c\overline{c}$. The same model dependence was observed in already published d + A data. Lastly, the p + p data are also directly compared with d + A data in mass and pT, and within the statistical accuracy no nuclear modification is seen.
Differential measurements of elliptic flow (v(2)) for Au+Au and Cu+Cu collisions at root s(NN)=200 GeV are used to test and validate predictions from perfect fluid hydrodynamics for scaling of v(2) ...with eccentricity, system size, and transverse kinetic energy (KET). For KET equivalent to m(T)-m up to similar to 1 GeV the scaling is compatible with hydrodynamic expansion of a thermalized fluid. For large values of KET mesons and baryons scale separately. Quark number scaling reveals a universal scaling of v(2) for both mesons and baryons over the full KET range for Au+Au. For Au+Au and Cu+Cu the scaling is more pronounced in terms of KET, rather than transverse momentum.
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