Measurement of two-particle correlations with respect to second- and third-order event planes in Au plus Au collisions at root s(NN)=200 GeV

We present measurements of azimuthal correlations of charged hadron pairs in root s(NN) = 200 GeV Au + Au collisions for the trigger and associated particle transverse-momentum ranges of 1 4 GeV/c) correlations is suppressed compared with that of correlations measured in p + p collisions. At the lowest associated particle p(T)(0.5 <p(T)(a) <1 GeV/c), the away-side shape and yield are modified relative to those in p + p collisions. These observations are consistent with the scenario of radiative-jet energy loss. For the low-p(T) trigger correlations (2 <p(T)(t) <4 GeV/c), a finite away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle Psi(2) and Psi(3). The angular correlations show an asymmetry when selecting the sign of the difference between the trigger-particle azimuthal angle and the Psi(2) event plane. This asymmetry and the measured suppression of the pair yield out-of-plane is consistent with a path-length-dependent energy loss. No Psi(3) dependence can be resolved within experimental uncertainties.Peer reviewe

Measurements of e(+)e(-) pairs from open heavy flavor in p plus p and d plus A collisions at root S-NN=200 GeV

We report a measurement of e(+)e(-) pairs from semileptonic heavy-flavor decays in p + p collisions at root S-NN = 200 GeV. The e(+)e(-) pair yield from b (b) over bar and c (c) over bar is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and p(T). We used three different event generators, PYTHIA, MC@NLO, and POWHEG, to simulate the e(+)e(-) spectra from c (c) over bar and b (b) over bar production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to 4 pi, significant differences are observed for the total cross section. These difference are less pronounced for b (b) over bar than for c (c) over bar. The same model dependence was observed in already published d + A data. The p + p data are also directly compared with d + A data in mass and p(T), and within the statistical accuracy no nuclear modification is seen.Peer reviewe

Measurement of J/Psi at forward and backward rapidity in p plus p, p plus Al, p + Au, and He-3+Au collisions at root s(NN)=200 GeV

Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of J/Psi measurements at forward and backward rapidity in various small collision systems, p + p, p + Al, p + Au, and He-3+Au, at root s(NN) = 200 GeV. The results are presented in the form of the observable RAB, the nuclear modification factor, a measure of the ratio of the J/Psi invariant yield compared to the scaled yield in p + p collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on J/Psi production with different projectile sizes p and He-3, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for p + Au and He-3+Au. However, for 0%-20% central collisions at backward rapidity, the modification factor for He-3+Au is found to be smaller than that for p + Au, with a mean fit to the ratio of 0.89 +/- 0.03(stat)+/- 0.08(syst), possibly indicating final state effects due to the larger projectile size.Peer reviewe

Low-momentum direct-photon measurement in Cu plus Cu collisions at root S-NN=200 GeV

We measured direct photons for p(T) <5 GeV/c in minimum bias and 0%-40% most-central events at midrapidity for Cu+Cu collisions at root S-NN = 200 GeV. The e(+)e(-) contribution from quasireal direct virtual photons has been determined as an excess over the known hadronic contributions in the e(+)e(-) mass distribution. A clear enhancement of photons over the binary scaled p+p fit is observed for p(T) <4 GeV/c in Cu+Cu data. The p(T) spectra are consistent with the Au+Au data covering a similar number of participants. The inverse slopes of the exponential fits to the excess after subtraction of the p+p baseline are 285 +/- 53 (stat) +/- 57(syst) MeV/c and 333 +/- 72(stat) +/- 45(syst) MeV/c for minimum bias and 0%-40% most-central events, respectively. The rapidity density, dN / dy, of photons demonstrates the same power law as a function of dN(ch)/d eta observed in Au+Au at the same collision energy.Peer reviewe

Measurement of the relative yields of psi(2S) to psi(1S) mesons produced at forward and backward rapidity in p plus p, p plus Al, p + Au, and He-3+Au collisions at root S-NN=200 GeV

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.Peer reviewe

Multiparticle azimuthal correlations for extracting event-by-event elliptic and triangular flow in Au plus Au collisions at root S-NN=200 GeV

We present measurements of elliptic and triangular azimuthal anisotropy of charged particles detected at forward rapidity 1 < vertical bar eta vertical bar < 3 in Au + Au collisions at root S-NN = 200 GeV, as a function of centrality. The multiparticle cumulant technique is used to obtain the elliptic flow coefficients v(2){2}, v(2){4}, v(2){6}, and v(2){8}, and triangular flow coefficients v(3){2} and v(3){4}. Using the small-variance limit, we estimate the mean and variance of the event-by-event v 2 distribution from v(2){2} and v(2){4}. In a complementary analysis, we also use a folding procedure to study the distributions of v(2) and v(3) directly, extracting both the mean and variance. Implications for initial geometrical fluctuations and their translation into the final-state momentum distributions are discussed.Peer reviewe

Polarization and cross section of midrapidity J/psi production in p plus p collisions at root s=510 GeV

The PHENIX experiment has measured the spin alignment for inclusive J/psi -> e(+) e(-) decays in protonproton collisions at root s = 510 GeV at midrapidity. The angular distributions have been measured in three different polarization frames, and the three decay angular coefficients have been extracted in a full two-dimensional analysis. Previously, PHENIX saw large longitudinal net polarization at forward rapidity at the same collision energy. This analysis at midrapidity, complementary to the previous PHENIX results, sees no sizable polarization in the measured transverse momentum range of 0.0 <p(T) <10.0 GeV/c. The results are consistent with a previous one-dimensional analysis at midrapidity at root s = 200 GeV. The transverse-momentum-dependent cross section for midrapidity J/psi production has additionally been measured, and after comparison to world data, a simple logarithmic dependence of the cross section on root s was found.Peer reviewe

Angular decay coefficients of J/psi mesons at forward rapidity from p plus p collisions at root s=510 GeV

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.Peer reviewe

Production of b(b)over-bar at forward rapidity in p plus p collisions at root s=510 GeV

The cross section of bottom quark-antiquark (b (b) over bar) production in p + p collisions at root s = 510 GeV is measured with the PHENIX detector at the Relativistic Heavy Ion Collider. The results are based on the yield of high mass, like-sign muon pairs measured within the PHENIX muon arm acceptance (1.2 mu +/-mu +/-)/dy = 0.16 +/- 0.01 (stat) +/- 0.02 (syst) +/- 0.02 (global) nb for like-sign muons in the rapidity and p(T) ranges 1.2 1 GeV/c, and dimuon mass of 5-10 GeV/c(2). The extrapolated total cross section at this energy for b (b) over bar production is 13.1 +/- 0.6 (stat) +/- 1.5 (syst) +/- 2.7 (global) mu b. The total cross section is compared to a perturbative quantum chromodynamics calculation and is consistent within uncertainties. The azimuthal opening angle between muon pairs from b (b) over bar decays and their p(T) distributions are compared to distributions generated using PS PYTHIA6, which includes next-to-leading order processes. The azimuthal correlations and pair p(T) distribution are not very well described by PYTHIA calculations, but are still consistent within uncertainties. Flavor creation and flavor excitation subprocesses are favored over gluon splitting.Peer reviewe