We report on the measurements of directed flow and elliptic flow $ν_{2}$ for hadrons ($π^{±}$, $Κ^{±}$, $Κ^{0}_{s}$, p, φ, Λ and $Ξ^{-}$) from Au+Au collisions at $ \sqrt{s_{NN}}$ = 3 GeV and for ...($π^{±}$, $Κ^{±}$, $p$ and $\bar{p}$) at 27 and 54.4 GeV with the STAR experiment. While at the two higher energy midcentral collisions the number-of-constituent-quark (NCQ) scaling holds, at 3 GeV the at midrapidity is negative for all hadrons and the NCQ scaling is absent. In addition, the slopes at midrapidity for almost all observed hadrons are found to be positive, implying dominant repulsive baryonic interactions. The features of negative $ν_{2}$ and positive $ν_{1}$ slope at 3 GeV can be reproduced with a baryonic mean-field in transport model calculations. These results imply that the medium in such collisions is likely characterized by baryonic interactions.
Measurement by the STAR experiment at RHIC of the cold nuclear matter (CNM) effects experienced by inclusive J / ψ at mid-rapidity in 0-100% p+Au collisions at s NN = 200 GeV is presented. Such ...effects are quantified utilizing the nuclear modification factor, R p Au , obtained by taking a ratio of J / ψ yield in p+Au collisions to that in p+p collisions scaled by the number of binary nucleon-nucleon collisions. The differential J / ψ yield in both p+p and p+Au collisions is measured through the dimuon decay channel, taking advantage of the trigger capability provided by the Muon Telescope Detector in the RHIC 2015 run. Consequently, the J / ψ R p Au is derived within the transverse momentum ( p T ) range of 0 to 10 GeV/c. A suppression of approximately 30% is observed for p T < 2 GeV/c, while J / ψ R p Au becomes compatible with unity for p T greater than 3 GeV/c, indicating the J / ψ yield is minimally affected by the CNM effects at high p T . Comparison to a similar measurement from 0-20% central Au+Au collisions reveals that the observed strong J / ψ suppression above 3 GeV/c is mostly due to the hot medium effects, providing strong evidence for the formation of the quark-gluon plasma in these collisions. Several model calculations show qualitative agreement with the measured J / ψ R p Au , while their agreement with the J / ψ yields in p+p and p+Au collisions is worse.
In high-energy heavy-ion collisions, partonic collectivity is evidenced by the constituent quark number scaling of elliptic flow anisotropy for identified hadrons. A breaking of this scaling and ...dominance of baryonic interactions is found for identified hadron collective flow measurements in $\sqrt{^{S}\text{NN}}$ = 3 GeV Au+Au collisions. In this paper, we report measurements of the first- and second-order azimuthal anisotropic parameters, v1 and v2, of light nuclei (d, t, 3He, 4He) produced in $\sqrt{^{S}\text{NN}}$ = 3 GeV Au+Au collisions at the STAR experiment. An atomic mass number scaling is found in the measured v1 slopes of light nuclei at mid-rapidity. For the measured v2 magnitude, a strong rapidity dependence is observed. Unlike v2 at higher collision energies, the v2 values at mid-rapidity for all light nuclei are negative and no scaling is observed with the atomic mass number. Calculations by the Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, are in good agreement with our observations, implying baryonic interactions dominate the collective dynamics in 3 GeV Au+Au collisions at RHIC.
In this article we describe the background challenges for the CUORE experiment posed by surface contamination of inert detector materials such as copper, and present three techniques explored to ...mitigate these backgrounds. Using data from a dedicated test apparatus constructed to validate and compare these techniques we demonstrate that copper surface contamination levels better than 10−7- 10−8 Bq/cm2 are achieved for 238U and 232Th. If these levels are reproduced in the final CUORE apparatus the projected 90% C.L. upper limit on the number of background counts in the region of interest is 0.02–0.03 counts/keV/kg/y depending on the adopted mitigation technique.
The chiral magnetic effect (CME) is predicted to occur as a consequence of a local violation of P and CP symmetries of the strong interaction amidst a strong electromagnetic field generated in ...relativistic heavy-ion collisions. Experimental manifestation of the CME involves a separation of positively and negatively charged hadrons along the direction of the magnetic field. Previous measurements of the CME-sensitive charge-separation observables remain inconclusive because of large background contributions. To better control the influence of signal and backgrounds, the STAR Collaboration performed a blind analysis of a large data sample of approximately 3.8 billion isobar collisions of $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr at √sNN = 200 GeV. Prior to the blind analysis, the CME signatures are predefined as a significant excess of the CME-sensitive observables in Ru+Ru collisions over those in Zr + Zr collisions, owing to a larger magnetic field in the former. A precision down to 0.4% is achieved, as anticipated, in the relative magnitudes of the pertinent observables between the two isobar systems. Observed differences in the multiplicity and flow harmonics at the matching centrality indicate that the magnitude of the CME background is different between the two species. Furthermore, no CME signature that satisfies the predefined criteria has been observed in isobar collisions in this blind analysis.
Global hyperon polarization, $\bar{P}_H$, in Au+Au collisions over a large range of collision energy, $\sqrt{s_{NN}}$, has recently been measured and successfully reproduced by hydrodynamic and ...transport models with intense fluid vorticity of the Quark-Gluon Plasma (QGP). While naïve extrapolation of data trends suggests a large $\bar{P}_H$ as the collision energy is reduced, the behavior of $\bar{P}_H$ at small $\sqrt{s_{NN}}$ < 7.7 GeV is unknown. Operating the STAR experiment in fixed-target mode, we have measured the polarization of Λ hyperons along the direction of global angular momentum in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The observation of substantial polarization of 4.91±0.81(stat.)±0.15(syst.)% in these collisions may require a reexamination of the viscosity of any fluid created in the collision, the thermalization timescale of rotational modes, and of hadronic mechanisms to produce global polarization.
PDF
