Transversity and Transverse-Momentum-Dependent Distribution Measurements from PHENIX and BRAHMS

A variety of measurements performed utilizing transversely polarized proton- proton collisions at the Relativistic Heavy Ion Collider (RHIC) are now avail- able. Recent results from the PHENIX and BRAHMS experiments are presented and discussed.Comment: 10 pages, 7 figures, to appear in the proceedings of the 2nd International Workshop on Transverse Polarization Phenomena in Hard Processes (Transversity 2008), Ferrara, Italy, May 2008. Replaced figure for 200 GeV proton and antiproton asymmetrie

Measurements of Multiparticle Correlations in d plus Au Collisions at 200, 62.4, 39, and 19.6 GeV and p plus Au Collisions at 200 GeV and Implications for Collective Behavior

Recently, multiparticle-correlation measurements of relativistic p/d(3)He + Au, p + Pb, and even p + p collisions show surprising collective signatures. Here, we present beam-energy-scan measurements of two, four-, and six-particle angular correlations in d + Au collisions at root s(NN) = 200, 62.4, 39, and 19.6 GeV. We also present measurements of two-and four-particle angular correlations in p + Au collisions at root s(NN) = 200 GeV. We find the four-particle cumulant to be real valued for d + Au collisions at all four energies. We also find that the four-particle cumulant in p + Au has the opposite sign as that in d + Au. Further, we find that the six-particle cumulant agrees with the four-particle cumulant in d + Au collisions at 200 GeV, indicating that nonflow effects are subdominant. These observations provide strong evidence that the correlations originate from the initial geometric configuration, which is then translated into the momentum distribution for all particles, commonly referred to as collectivity.Peer reviewe

Measurement of long-range angular correlations and azimuthal anisotropies in high-multiplicity p plus Au collisions at root S-NN=200 GeV

We present measurements of long-range angular correlations and the transverse momentum dependence of elliptic flow v(2) in high-multiplicity p + Au collisions at root S-NN = 200 GeV. A comparison of these results to previous measurements in high-multiplicity d + Au and He-3+Au collisions demonstrates a relation between v(2) and the initial collision eccentricity epsilon(2), suggesting that the observed momentum-space azimuthal anisotropies in these small systems have a collective origin and reflect the initial geometry. Good agreement is observed between the measured v(2) and hydrodynamic calculations for all systems, and an argument disfavoring theoretical explanations based on initial momentum-space domain correlations is presented. The set of measurements presented here allows us to leverage the distinct intrinsic geometry of each of these systems to distinguish between different theoretical descriptions of the long-range correlations observed in small collision systems.Peer reviewe

Nuclear Dependence of the Transverse-Single-Spin Asymmetry for Forward Neutron Production in Polarized p plus A Collisions at root S-NN=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.Peer reviewe

Global Analysis of Fragmentation Functions for Eta Mesons

Fragmentation functions for eta mesons are extracted at next-to-leading order accuracy of QCD in a global analysis of data taken in electron-positron annihilation and proton-proton scattering experiments. The obtained parametrization is in good agreement with all data sets analyzed and can be utilized, for instance, in future studies of double-spin asymmetries for single-inclusive eta production. The Lagrange multiplier technique is used to estimate the uncertainties of the fragmentation functions and to assess the role of the different data sets in constraining them.Comment: 11 pages, 8 figures, updated reference