Elliptic flow contribution to two-particle correlations at different orientations to the reaction plane

Collective anisotropic particle flow, a general phenomenon present in relativistic heavy-ion collisions, can be separated from direct particle-particle correlations of different physics origin by virtue of its specific azimuthal pattern. We provide expressions for flow-induced two-particle azimuthal correlations, if one of the particles is detected under fixed directions with respect to the reaction plane. We consider an ideal case when the reaction plane angle is exactly known, as well as present the general expressions in case of finite event-plane resolution. We foresee applications for the study of generic two-particle correlations at large transverse momentum originating from jet fragmentation.Comment: 5 pages, 3 figures, to be published as Rapid Communications in Phys.Rev.C Re-submit paper to with small improvements in text for better understanding, some minor changes in notation, and correcting one formula where a summation was forgotten. One new reference, one reference to conference report removed since full paper was already reference

Azimuthal transverse single-spin asymmetries of inclusive jets and charged pions within jets from polarized-proton collisions at √s=500 GeV

We report the first measurements of transverse single-spin asymmetries for inclusive jet and jet+π± production at midrapidity from transversely polarized proton-proton collisions at √s=500  GeV. The data were collected in 2011 with the STAR detector sampled from 23  pb−1 integrated luminosity with an average beam polarization of 53%. Asymmetries are reported for jets with transverse momenta 6<pT<55  GeV/c and pseudorapidity |η|<1. Presented are measurements of the inclusive-jet azimuthal transverse single-spin asymmetry, sensitive to twist-3 initial-state quark-gluon correlators; the Collins asymmetry, sensitive to quark transversity coupled to the polarized Collins fragmentation function; and the first measurement of the “Collins-like” asymmetry, sensitive to linearly polarized gluons. Within the present statistical precision, inclusive-jet and Collins-like asymmetries are small, with the latter allowing the first experimental constraints on gluon linear polarization in a polarized proton. At higher values of jet transverse momenta, we observe the first nonzero Collins asymmetries in polarized-proton collisions, with a statistical significance of greater than 5σ. The results span a range of x similar to results from semi-inclusive deep-inelastic scattering but at much higher Q2. The Collins results enable tests of universality and factorization breaking in the transverse momentum-dependent formulation of perturbative quantum chromodynamics

Beam-Energy Dependence of Directed Flow of Λ, ¯Λ, K±, K0s, and ϕ in Au+Au Collisions

Rapidity-odd directed-flow measurements at midrapidity are presented for Λ, ¯Λ, K±, K0s, and ϕ 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

Nuclear Dependence of the Transverse-Single-Spin Asymmetry for Forward Neutron Production in Polarized p+A Collisions at √sNN=200 GeV

During 2015, the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized p+p collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in p+p collisions predicts only a moderate atomic-mass-number (A) dependence. In contrast, the asymmetries observed at RHIC in p+A collisions showed a surprisingly strong A dependence in inclusive forward neutron production. The observed asymmetry in p+Al collisions is much smaller, while the asymmetry in p+Au collisions is a factor of 3 larger in absolute value and of opposite sign. The interplay of different neutron production mechanisms is discussed as a possible explanation of the observed A dependence

Bulk properties of the medium produced in relativistic heavy-ion collisions from the beam energy scan program

We present measurements of bulk properties of the matter produced in Au+Au collisions at √sNN=7.7,11.5,19.6,27, and 39 GeV using identified hadrons (π±, K±, p, and ¯p) from the STAR experiment in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). Midrapidity (|y|<0.1) results for multiplicity densities dN/dy, average transverse momenta ⟨pT⟩, and particle ratios are presented. The chemical and kinetic freeze-out dynamics at these energies are discussed and presented as a function of collision centrality and energy. These results constitute the systematic measurements of bulk properties of matter formed in heavy-ion collisions over a broad range of energy (or baryon chemical potential) at RHIC

Coherent diffractive photoproduction of ρ0 mesons on gold nuclei at 200 GeV/nucleon-pair at the Relativistic Heavy Ion Collider

The STAR Collaboration reports on the photoproduction of π+π− pairs in gold-gold 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 ρ0 and ω resonances and a direct π+π− continuum. This is the first observation of the ω in ultraperipheral collisions, and the first measurement of ρ−ω interference at energies where photoproduction is dominated by Pomeron exchange. The ω amplitude is consistent with the measured γp→ωp cross section, a classical Glauber calculation, and the ω→π+π− branching ratio. The ω phase angle is similar to that observed at much lower energies, showing that the ρ−ω phase difference does not depend significantly on photon energy.The ρ0 differential cross section dσ/dt exhibits a clear diffraction pattern, compatible with scattering from a gold nucleus, with two minima visible. The positions of the diffractive minima agree better with the predictions of a quantum Glauber calculation that does not include nuclear shadowing than with a calculation that does include shadowing

Collective Flow Measurements from the PHENIX Experiment

Recent collective flow measurements including higher moment event anisotropy from the PHENIX experiment are presented, and the particle type, beam energy dependence and the relation with jet modification are discussed. The measured higher order event anisotropy with event plane defined at forward rapidities and the long range correlation with large $\eta$ gaps are both consistent with initial geometrical fluctuation of the participating nuclei. In 200 GeV Au+Au collisions, higher order event anisotropy, especially simultaneous description of v$_2$ and v$_3$, is found to give an additional constraining power on initial geometrical condition and viscosity in the hydrodynamic calculations. v$_2$, v$_3$ and v$_4$ are almost unchanged down to the lower colliding energy at 39 GeV in Au+Au. The measured two particle correlation with subtraction of the measured v$_n$ parameters shows a significant effect on the shape and yield in the associate particle $\Delta\phi$ distribution with respect to the azimuthal direction of trigger particles. However some medium responses from jet suppression or jet modification seems to be observed. Direct photon v$_2$ has been measured in 200 GeV Au+Au collisions. The measured v$_2$ is found to be small at high p$_{\rm T}$ as expected from non-suppressed direct photon R$_{\rm AA}$ $\simeq$ 1, which can be understood as being dominated by prompt photons from initial hard scattering. On the other hand, at lower p$_{\rm T}$ $<$ 4 GeV/c it is found to be significantly larger than zero, which is comparable to other hadron v$_2$, where thermal photons are observed.Comment: 8 pages, 10 figures, Quark Matter 2011 proceeding

Conference Summary of QNP2018

This report is the summary of the Eighth International Conference on Quarks and Nuclear Physics (QNP2018). Hadron and nuclear physics is the field to investigate high-density quantum many-body systems bound by strong interactions. It is intended to clarify matter generation of universe and properties of quark-hadron many-body systems. The QNP is an international conference which covers a wide range of hadron and nuclear physics, including quark and gluon structure of hadrons, hadron spectroscopy, hadron interactions and nuclear structure, hot and cold dense matter, and experimental facilities. First, I introduce the current status of the hadron and nuclear physics field related to this conference. Next, the organization of the conference is explained, and a brief overview of major recent developments is discussed by selecting topics from discussions at the plenary sessions. They include rapidly-developing field of gravitational waves and nuclear physics, hadron interactions and nuclear structure with strangeness, lattice QCD, hadron spectroscopy, nucleon structure, heavy-ion physics, hadrons in nuclear medium, and experimental facilities of EIC, GSI-FAIR, JLab, J-PARC, Super-KEKB, and others. Nuclear physics is at a fortunate time to push various projects at these facilities. However, we should note that the projects need to be developed together with related studies in other fields such as gravitational physics, astrophysics, condensed-matter physics, particle physics, and fundamental quantum physics.Comment: 10 pages, LaTeX, 1 style file, 3 figure files, Proceedings of Eighth International Conference on Quarks and Nuclear Physics (QNP2018), November 13-17, 2018, Tsukuba, Japa

Simple analytic solution of fireball hydrodynamics

A new family of simple analytic solutions of hydrodynamics is found for non-relativistic, rotationally symmetric fireballs assuming an ideal gas equation of state. The solution features linear flow profile and a non-trivial transverse temperature profile. The radial temperature gradient vanishes only in the collisionless gas limit. The Zimanyi-Bondorf-Garpman solution and the Buda-Lund parameterization of expanding hydrodynamical sources are recovered as special cases. The results are applied to predict new features of proton-proton correlations and spectra data at 1.93 AGeV Ni + Ni reactions.Comment: Latex, Revte

Boundary and expansion effects on two-pion correlation functions in relativistic heavy-ion collisions

We examine the effects that a confining boundary together with hydrodynamical expansion play on two-pion distributions in relativistic heavy-ion collisions. We show that the effects arise from the introduction of further correlations due both to collective motion and the system's finite size. As is well known, the former leads to a reduction in the apparent source radius with increasing average pair momentum K. However, for small K, the presence of the boundary leads to a decrease of the apparent source radius with decreasing K. These two competing effects produce a maximum for the effective source radius as a function of K.Comment: 6 pages, 5 Eps figures, uses RevTeX and epsfi