We report the first measurement of the inclusive jet and the dijet longitudinal double-spin asymmetries, ALL, at midrapidity in polarized pp collisions at a center-of-mass energy s=510 GeV. The ...inclusive jet ALL measurement is sensitive to the gluon helicity distribution down to a gluon momentum fraction of x≈0.015, while the dijet measurements, separated into four jet-pair topologies, provide constraints on the x dependence of the gluon polarization. Both results are consistent with previous measurements made at s=200 GeV in the overlapping kinematic region, x>0.05, and show good agreement with predictions from recent next-to-leading order global analyses.
In this paper we look for correlations between intermediate pT particle pairs and the v2 of the remaining low pT particles. We find that the shape of the flow vector distribution, which is calculated ...from all low pT tracks, depends in a non-trivial way on the angular separation between the high pT particle pairs in the event. Our analysis is based on 200 GeV Au+Au collisions measured with the STAR detector.
In this paper we look for correlations between intermediate
p
T
particle pairs and the
v
2
of the remaining low
p
T
particles. We find that the shape of the flow vector distribution, which is ...calculated from all low
p
T
tracks, depends in a non-trivial way on the angular separation between the high
p
T
particle pairs in the event. Our analysis is based on 200 GeV Au+Au collisions measured with the STAR detector.
We report measurements of the nuclear modification factor RCP for charged hadrons as well as identified π+(−), K+(−), and p(p¯) for Au+Au collision energies of sNN=7.7, 11.5, 14.5, 19.6, 27, 39, and ...62.4 GeV. We observe a clear high-pT net suppression in central collisions at 62.4 GeV for charged hadrons which evolves smoothly to a large net enhancement at lower energies. This trend is driven by the evolution of the pion spectra but is also very similar for the kaon spectra. While the magnitude of the proton RCP at high pT does depend on the collision energy, neither the proton nor the antiproton RCP at high pT exhibit net suppression at any energy. A study of how the binary collision-scaled high-pT yield evolves with centrality reveals a nonmonotonic shape that is consistent with the idea that jet quenching is increasing faster than the combined phenomena that lead to enhancement.
Here, the STAR Collaboration reports on the photoproduction of π+π- pairs in goldgold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly-real ...photon emitted by one ion scatters from the other ion. We fit the π+π- invariant mass spectrum with a combination of 0 and ! resonances and a direct π+π- continuum. This is the first observation of the ! in ultra-peripheral collisions, and the first measurement of ρ - ω interference at energies where photoproduction is dominated by Pomeron exchange.
We present Lambda Lambda correlation measurements in heavy-ion collisions for Au + Au collisions at root s(NN) = 200 GeV using the STAR experiment at the Relativistic Heavy-Ion Collider. The ...Lednicky-Lyuboshitz analytical model has been used to fit the data to obtain a source size, a scattering length and an effective range. Implications of the measurement of the Lambda Lambda correlation function and interaction parameters for dihyperon searches are discussed.
We present measurements of second-order azimuthal anisotropy (v2) at midrapidity (|y| < 1.0) for light nuclei d,t,3He (for sNN=200, 62.4, 39, 27, 19.6, 11.5, and 7.7 GeV) and antinuclei $ ...\overline{d}\ $; (sNN=200, 62.4, 39, 27, and 19.6 GeV) and 3H$ \overline{e}\ $(sNN=200 GeV) in the STAR (Solenoidal Tracker at RHIC) experiment. The v2 for these light nuclei produced in heavy-ion collisions is compared with those for p and $ \overline{p}\ $. We observe mass ordering in nuclei v2(pT) at low transverse momenta (pT < 2.0 GeV/c). We also find a centrality dependence of v2 for d and $ \overline{d}\ $. The magnitude of v2 for t and 3He agree within statistical errors. Light-nuclei v2 are compared with predictions from a blast-wave model. Atomic mass number (A) scaling of light-nuclei v2(pT) seems to hold for pT/A < 1.5GeV/c. Results on light-nuclei v2 from a transport-plus-coalescence model are consistent with the experimental measurements.
Here, we report a measurement of cumulants and correlation functions of event-by-event proton multiplicity distributions from fixed-target Au+Au collisions at $\sqrt{s_\text{NN}}$ = 3 GeV measured by ...the STAR experiment. Protons are identified within the rapidity (y) and transverse momentum ($p_T$) region –0:9 < $\textit{y}$ < 0 and 0:4 < pT < 2:0 GeV/c in the center-of-mass frame. A systematic analysis of the proton cumulants and correlation functions up to sixth-order as well as the corresponding ratios as a function of the collision centrality, $p_T$, and $\textit{y}$ are presented. The effect of pileup and initial volume fluctuations on these observables and the respective corrections are discussed in detail. The results are compared to calculations from the hadronic transport UrQMD model as well as a hydrodynamic model. In the most central 5% collisions, the value of proton cumulant ratio $C_4 = C_2$ is negative, drastically different from the values observed in Au+Au collisions at higher energies. Compared to model calculations including Lattice QCD, a hadronic transport model, and a hydrodynamic model, the strong suppression in the ratio of $C_4/C_2$ at 3 GeV Au+Au collisions indicates an energy regime dominated by hadronic interactions.
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