J/ψ\rm{J}/\psi production at low transverse momentum in p+p and d+Au collisions at sNN\sqrt{s_{NN}} = 200 GeV

We report on the measurement of $\rm{J}/\psi$ production in the dielectron channel at mid-rapidity (|y|<1) in p+p and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment at the Relativistic Heavy Ion Collider. The transverse momentum $p_{T}$ spectra in p+p for $p_{T}$ < 4 GeV/c and d+Au collisions for $p_{T}$ < 3 GeV/c are presented. These measurements extend the STAR coverage for $\rm{J}/\psi$ production in p+p collisions to low $p_{T}$. The $$ from the measured $\rm{J}/\psi$ invariant cross section in p+p and d+Au collisions are evaluated and compared to similar measurements at other collision energies. The nuclear modification factor for $\rm{J}/\psi$ is extracted as a function of $p_{T}$ and collision centrality in d+Au and compared to model calculations using the modified nuclear Parton Distribution Function and a final-state $\rm{J}/\psi$ nuclear absorption cross section

Di-hadron correlations with identified leading hadrons in 200 GeV Au+Au and d+Au collisions at STAR

The STAR Collaboration presents for the first time two-dimensional di-hadron correlations with identified leading hadrons in 200 GeV central Au + Au and minimum-bias d + Au collisions to explore hadronization mechanisms in the quark gluon plasma. The enhancement of the jet-like yield for leading pions in Au + Au data with respect to the d + Au reference and the absence of such an enhancement for leading non-pions (protons and kaons) are discussed within the context of a quark recombination scenario. The correlated yield at large angles, specifically in the ridge region , is found to be significantly higher for leading non-pions than pions. The consistencies of the constituent quark scaling, azimuthal harmonic model and a mini-jet modification model description of the data are tested, providing further constraints on hadronization

Energy dependence of J/\u3c8 production in Au + Au collisions at s NN =39,62.4 and 200GeV

The inclusive J/\u3c8 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/\u3c8 production, with respect to the production in p+p scaled by the number of binary nucleon\u2013nucleon 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/\u3c8 production due to the color screening effect and J/\u3c8 regeneration from recombination of uncorrelated charm\u2013anticharm quark pairs

Collision energy dependence of moments of net-kaon multiplicity distributions at RHIC

Fluctuations of conserved quantities such as baryon number, charge, and strangeness are sensitive to the correlation length of the hot and dense matter created in relativistic heavy-ion collisions and can be used to search for the QCD critical point. We report the first measurements of the moments of net-kaon multiplicity distributions in Au+Au collisions at sNN=7.7 , 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV. The collision centrality and energy dependence of the mean ( M ), variance ( \u3c32 ), skewness ( S ), and kurtosis ( \u3ba ) for net-kaon multiplicity distributions as well as the ratio \u3c32/M and the products S\u3c3 and \u3ba\u3c32 are presented. Comparisons are made with Poisson and negative binomial baseline calculations as well as with UrQMD, a transport model (UrQMD) that does not include effects from the QCD critical point. Within current uncertainties, the net-kaon cumulant ratios appear to be monotonic as a function of collision energy

Direct virtual photon production in Au+Au collisions atsNN=200\ua0GeV

We report the direct virtual photon invariant yields in the transverse momentum ranges 16 GeV/c the production follows TAA scaling. Model calculations with contributions from thermal radiation and initial hard parton scattering are consistent within uncertainties with the direct virtual photon invariant yield

Beam-Energy Dependence of Directed Flow of \u39b, \u39b , K\ub1, Ks0, and \u3c6 in Au+Au Collisions

Rapidity-odd directed-flow measurements at midrapidity are presented for \u39b, \u39b\uaf, K\ub1, Ks0, and \u3d5 at sNN=7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV in Au+Au collisions recorded by the Solenoidal Tracker detector at the Relativistic Heavy Ion Collider. These measurements greatly expand the scope of data available to constrain models with differing prescriptions for the equation of state of quantum chromodynamics. Results show good sensitivity for testing a picture where flow is assumed to be imposed before hadron formation and the observed particles are assumed to form via coalescence of constituent quarks. The pattern of departure from a coalescence-inspired sum rule can be a valuable new tool for probing the collision dynamics

The proton\u2013\u3a9 correlation function in Au\u202f+\u202fAu collisions at s NN =200GeV

We present the first measurement of the proton\u2013\u3a9 correlation function in heavy-ion collisions for the central (0\u201340%) and peripheral (40\u201380%) Au\u202f+\u202fAu collisions at GeV by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). Predictions for the ratio of peripheral collisions to central collisions for the proton\u2013\u3a9 correlation function are sensitive to the presence of a nucleon\u2013\u3a9 bound state. These predictions are based on the proton\u2013\u3a9 interaction extracted from -flavor lattice QCD calculations at the physical point. The measured ratio of the proton\u2013\u3a9 correlation function between the peripheral (small system) and central (large system) collisions is less than unity for relative momentum smaller than 40 MeV/c. Comparison of our measured correlation ratio with theoretical calculation slightly favors a proton\u2013\u3a9 bound system with a binding energy of 3c 27 MeV

Measurement of the longitudinal spin asymmetries for weak boson production in proton-proton collisions at s=510\u2009\u2009GeV

We report new STAR measurements of the single-spin asymmetries AL for W+ and W- bosons produced in polarized proton-proton collisions at s=510\u2009\u2009GeV as a function of the decay-positron and decay-electron pseudorapidity. The data were obtained in 2013 and correspond to an integrated luminosity of 250\u2009\u2009pb-1. The results are combined with previous results obtained with 86\u2009\u2009pb-1. A comparison with theoretical expectations based on polarized lepton-nucleon deep-inelastic scattering and prior polarized proton-proton data suggests a difference between the u\uaf and d\uaf quark helicity distributions for 0.05<x<0.25. In addition, we report new results for the double-spin asymmetries ALL for W\ub1, as well as AL for Z/\u3b3* production and subsequent decay into electron-positron pairs

Measurement of interaction between antiprotons

One of the primary goals of nuclear physics is to understand the force between nucleons, which is a necessary step for understanding the structure of nuclei and how nuclei interact with each other. Rutherford discovered the atomic nucleus in 1911, and the large body of knowledge about the nuclear force since acquired was derived from studies made on nucleons or nuclei. Although antinuclei up to antihelium-4 have been discovered and their masses measured, we have no direct knowledge of the nuclear force between antinucleons. Here, we study antiproton pair correlations among data taken by the STAR experiment at the Relativistic Heavy Ion Collider and show that the force between two antiprotons is attractive. In addition, we report two key parameters that characterize the corresponding strong interaction: namely, the scattering length (f0) and effective range (d0). As direct information on the interaction between two antiprotons, one of the simplest systems of antinucleons, our result provides a fundamental ingredient for understanding the structure of more complex antinuclei and their properties

\u39b \u39b correlation function in Au+Au collisions at sNN =200GeV

We present \u39b\u39b correlation measurements in heavy-ion collisions for Au+Au collisions at sNN=200\u2009\u2009GeV using the STAR experiment at the Relativistic Heavy-Ion Collider. The Lednick\ufd-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 \u39b\u39b correlation function and interaction parameters for dihyperon searches are discussed