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Aidala, C.,Akiba, Y.,Alfred, M.,Andrieux, V.,Aoki, K.,Apadula, N.,Asano, H.,Ayuso, C.,Azmoun, B.,Babintsev, V.,Bandara, N. S.,Barish, K. N.,Bathe, S.,Bazilevsky, A.,Beaumier, M.,Belmont, R.,Berdnikov, American Physical Society 2017 Physical Review C Vol.95 No.3
<P>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.</P>
Aidala, C.,Akiba, Y.,Alfred, M.,Andrieux, V.,Aoki, K.,Apadula, N.,Asano, H.,Ayuso, C.,Azmoun, B.,Babintsev, V.,Bagoly, A.,Bandara, N. S.,Barish, K. N.,Bathe, S.,Bazilevsky, A.,Beaumier, M.,Belmont, R. American Physical Society 2018 Physical review letters Vol.120 No.2
<P>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.</P>
Adare, A.,Aidala, C.,Ajitanand, N. N.,Akiba, Y.,Alfred, M.,Andrieux, V.,Aoki, K.,Apadula, N.,Asano, H.,Ayuso, C.,Azmoun, B.,Babintsev, V.,Bai, M.,Bandara, N. S.,Bannier, B.,Barish, K. N.,Bathe, S.,Baz American Physical Society 2017 Physical Review C Vol.95 No.3
<P>The PHENIX Collaboration has measured the ratio of the yields of psi(2S) to psi(1S) mesons produced in p + p, p + Al, p + Au, and He-3+Au collisions at root S-NN = 200 GeV over the forward and backward rapidity intervals 1.2 < | y | < 2.2. We find that the ratio in p + p collisions is consistent with measurements at other collision energies. In collisions with nuclei, we find that in the forward (p-going or He-3-going) direction, the relative yield of psi(2S) mesons to psi(1S) mesons is consistent with the value measured in p + p collisions. However, in the backward (nucleus-going) direction, the psi(2S) meson is preferentially suppressed by a factor of similar to 2. This suppression is attributed in some models to the breakup of the weakly bound psi(2S) meson through final-state interactions with comoving particles, which have a higher density in the nucleus-going direction. These breakup effects may compete with color screening in a deconfined quark-gluon plasma to produce sequential suppression of excited quarkonia states.</P>
Angular decay coefficients of J/ψ mesons at forward rapidity from p+p collisions at s=510 GeV
Adare, A.,Aidala, C.,Ajitanand, N. N.,Akiba, Y.,Akimoto, R.,Alfred, M.,Andrieux, V.,Aoki, K.,Apadula, N.,Aramaki, Y.,Asano, H.,Atomssa, E. T.,Awes, T. C.,Ayuso, C.,Azmoun, B.,Babintsev, V.,Bai, M.,Ban American Physical Society 2017 Physical Review D Vol.95 No.9
<P>We report the first measurement of the full angular distribution for inclusive J/psi -> mu(+)mu(-) decays in p + p collisions at root s = 510 GeV. The measurements are made for J/psi transverse momentum 2 < p(T) < 10 GeV /c and rapidity 1.2 < y < 2.2 in the Helicity, Collins-Soper, and Gottfried-Jackson reference frames. In all frames the polar coefficient lambda theta is strongly negative at low p(T) and becomes close to zero at high p(T), while the azimuthal coefficient lambda phi is close to zero at low p(T), and becomes slightly negative at higher p(T). The frame-independent coefficient lambda is strongly negative at all p(T) in all frames. The data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.</P>
Adare, A.,Aidala, C.,Ajitanand, N. N.,Akiba, Y.,Akimoto, R.,Alexander, J.,Alfred, M.,Andrieux, V.,Aoki, K.,Apadula, N.,Aramaki, Y.,Asano, H.,Atomssa, E. T.,Awes, T. C.,Ayuso, C.,Azmoun, B.,Babintsev, American Physical Society 2017 Physical Review D Vol.95 No.7
<P>Dihadron and isolated direct photon-hadron angular correlations are measured in p + p collisions at root s = 510 GeV. Correlations of charged hadrons of 0.7 < p(T) < 10 GeV/c with pi(0) mesons of 4 < p(T) < 15 GeV/c or isolated direct photons of 7 < p(T) < 15 GeV/c are used to study nonperturbative effects generated by initial-state partonic transverse momentum and final-state transverse momentum from fragmentation. The nonperturbative behavior is characterized by measuring the out-of-plane transverse momentum component p(out) perpendicular to the axis of the trigger particle, which is the high-p(T) direct photon or pi(0). Nonperturbative evolution effects are extracted from Gaussian fits to the away-side inclusive-charged-hadron yields for different trigger-particle transverse momenta (p(T)(trig)). The Gaussian widths and root mean square of p(out) are reported as a function of the interaction hard scale p(T)(trig) to investigate possible transverse-momentum-dependent evolution differences between the pi(0)-h(+/-) and direct photon-h(+/-) correlations and factorization breaking effects. The widths are found to decrease with p(T)(trig) , which indicates that the Collins-Soper-Sterman soft factor is not driving the evolution with the hard scale in nearly back-to-back dihadron and direct photon-hadron production in p + p collisions. This behavior is in contrast to Drell-Yan and semi-inclusive deep-inelastic scattering measurements.</P>