We present first measurements of the phi-meson elliptic flow (v2(pT)) and high-statistics pT distributions for different centralities from radical sNN=200 GeV Au+Au collisions at RHIC. In minimum ...bias collisions the v2 of the phi meson is consistent with the trend observed for mesons. The ratio of the yields of the Omega to those of the phi as a function of transverse momentum is consistent with a model based on the recombination of thermal s quarks up to pT approximately 4 GeV/c, but disagrees at higher momenta. The nuclear modification factor (R CP) of phi follows the trend observed in the K S 0 mesons rather than in Lambda baryons, supporting baryon-meson scaling. These data are consistent with phi mesons in central Au+Au collisions being created via coalescence of thermalized s quarks and the formation of a hot and dense matter with partonic collectivity at RHIC.
The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-\(\pi^0\)s produced at forward pseudorapidities (\(2.6<\eta<4.0\)) in \(p\)+\(p\), \(p+\)Al, and \(p+\)Au ...collisions at a center-of-mass energy of 200 GeV. We observe a clear suppression of the correlated yields of back-to-back \(\pi^0\) pairs in \(p+\)Al and \(p+\)Au collisions compared to the \(p\)+\(p\) data. The observed suppression of back-to-back pairs as a function of transverse momentum suggests nonlinear gluon dynamics arising at high parton densities. The larger suppression found in \(p+\)Au relative to \(p+\)Al collisions exhibits a dependence of the saturation scale, \(Q_s^2\), on the mass number, \(A\). A linear scaling of the suppression with \(A^{1/3}\) is observed with a slope of \(-0.09\) \(\pm\) \(0.01\).
Quark interactions with topological gluon configurations can induce local chirality imbalance and parity violation in quantum chromodynamics, which can lead to the chiral magnetic effect (CME) -- an ...electric charge separation along the strong magnetic field in relativistic heavy-ion collisions. The CME-sensitive azimuthal correlator observable (\(\Delta\gamma\)) is contaminated by background arising, in part, from resonance decays coupled with elliptic anisotropy (\(v_{2}\)). We report here differential measurements of the correlator as a function of the pair invariant mass (\(m_{\rm inv}\)) in 20-50\% centrality Au+Au collisions at \(\sqrt{s_{_{\rm NN}}}\)= 200 GeV by the STAR experiment at RHIC. Strong resonance background contributions to \(\Delta\gamma\) are observed. At large \(m_{\rm inv}\) where this background is significantly reduced, the \(\Delta\gamma\) value is found to be significantly smaller. An event-shape-engineering technique is deployed to determine the \(v_{2}\) background shape as a function of \(m_{\rm inv}\). We extract a \(v_2\)-independent and \(m_{\rm inv}\)-averaged signal \(\Delta\gamma_{\rm sig}\) = (0.03 \(\pm\) 0.06 \(\pm\) 0.08) \(\times10^{-4}\), or \((2\pm4\pm5)\%\) of the inclusive \(\Delta\gamma(m_{\rm inv}>0.4\) GeV/\(c^2\))\( =(1.58 \pm 0.02 \pm 0.02) \times10^{-4}\), within pion \(p_{T}\) = 0.2 - 0.8~\gevc and averaged over pseudorapidity ranges of \(-1 < \eta < -0.05\) and \(0.05 < \eta < 1\). This represents an upper limit of \(0.23\times10^{-4}\), or \(15\%\) of the inclusive result, at \(95\%\) confidence level for the \(m_{\rm inv}\)-integrated CME contribution.
The STAR collaboration at the BNL Relativistic Heavy-Ion Collider (RHIC) reports measurements of the inclusive yield of nonphotonic electrons, which arise dominantly from semileptonic decays of heavy ...flavor mesons, over a broad range of transverse momenta (1.2<p(T)<10 GeV/c) in p+p, d+Au, and Au+Au collisions at sqrts_{NN}=200 GeV. The nonphotonic electron yield exhibits an unexpectedly large suppression in central Au+Au collisions at high p(T), suggesting substantial heavy-quark energy loss at RHIC. The centrality and p(T) dependences of the suppression provide constraints on theoretical models of suppression.
The characterization of sewage sludge proteins is necessary to better understand their degradation by microbial populations when sludges are utilized for land application. The objective of this study ...was to characterize the molecular weights of extractable sewage sludge proteins by dialysis partitioning and polyacrylamide gel electrophoretic (PAGE) separation. Sewage sludges obtained from seven municipalities were extracted using H2O and 1 M NaOH followed by purification and concentration to facilitate molecular weight determinations. Dialysis partitioning of proteins showed that the majority of these compounds had molecular weights 14 000 (i.e., they were not retained by dialysis membrane). The separation of proteins by PAGE also showed that the bulk of H2O and 1 M NaOH soluble proteins were of low molecular weight ( 17 000). This indicated considerable proteolysis during waste treatment processing. Thus, the extractable sludge proteins appeared to be primarily poly- and oligopeptides rather than intact proteins. Based on these findings, sludge proteinaceous materials would be expected to degrade rapidly in soil due to the many soil microorganisms capable of utilizing protein degradation products
Partons traversing the strongly interacting medium produced in heavy-ion collisions are expected to lose energy depending on their color charge and mass. We measure the nuclear modification factors ...for charm- and bottom-decay electrons, defined as the ratio of yields, scaled by the number of binary nucleon-nucleon collisions, in \(\sqrt{s_{\rm NN}}\) = 200 GeV Au+Au collisions to \(p\)+\(p\) collisions (\(R_{\rm AA}\)), or in central to peripheral Au+Au collisions (\(R_{\rm CP}\)). We find the bottom-decay electron \(R_{\rm AA}\) and \(R_{\rm CP}\) to be significantly higher than that of charm-decay electrons. Model calculations including mass-dependent parton energy loss in a strongly coupled medium are consistent with the measured data. These observations provide clear evidence of mass ordering of charm and bottom quark energy loss when traversing through the strongly coupled medium created in heavy-ion collisions.
We present the scaling properties of Lambda, Xi, and Omega in midrapidity Au+Au collisions at the Brookhaven National Laboratory Relativistic Heavy Ion Collider at sqrts_{NN}=200 GeV. The yield of ...multistrange baryons per participant nucleon increases from peripheral to central collisions more rapidly than that of Lambda, indicating an increase of the strange-quark density of the matter produced. The strange phase-space occupancy factor gamma_{s} approaches unity for the most central collisions. Moreover, the nuclear modification factors of p, Lambda, and Xi are consistent with each other for 2<p_{T}<5 GeV/c in agreement with a scenario of hadron formation from constituent quark degrees of freedom.
Phys. Rev. C. 107. 034907 (2023) We report the measurement of $K^{*0}$ meson at midrapidity ($|y|<$ 1.0) in
Au+Au collisions at $\sqrt{s_{\rm NN}}$~=~7.7, 11.5, 14.5, 19.6, 27 and 39 GeV
collected by ...the STAR experiment during the RHIC beam energy scan (BES)
program. The transverse momentum spectra, yield, and average transverse
momentum of $K^{*0}$ are presented as functions of collision centrality and
beam energy. The $K^{*0}/K$ yield ratios are presented for different collision
centrality intervals and beam energies. The $K^{*0}/K$ ratio in heavy-ion
collisions are observed to be smaller than that in small system collisions (e+e
and p+p). The $K^{*0}/K$ ratio follows a similar centrality dependence to that
observed in previous RHIC and LHC measurements. The data favor the scenario of
the dominance of hadronic re-scattering over regeneration for $K^{*0}$
production in the hadronic phase of the medium.
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