69 research outputs found
Measurements of B→J/ψ at forward rapidity in p+p collisions at √s=510 GeV
No full textWe report the first measurement of the fraction of J=ψ mesons coming from B-meson decay (FB→J=ψ ) in p þ p collisions at ffiffi s p ¼ 510 GeV. The measurement is performed using the forward silicon vertex detector and central vertex detector at PHENIX, which provide precise tracking and distance-of-closestapproach determinations, enabling the statistical separation of J=ψ due to B-meson decays from prompt J=ψ. The measured value of FB→J=ψ is 8.1% 2.3%ðstatÞ 1.9%ðsystÞ for J=ψ with transverse momenta 0 \u3c pT \u3c 5 GeV=c and rapidity 1.2 \u3c jyj \u3c 2.2. The measured fraction FB→J=ψ at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-toleading-logarithm and color-evaporation-model predictions. The bb¯ cross section per unit rapidity [dσ=dyðpp → bb¯Þ] extracted from the obtained FB→J=ψ and the PHENIX inclusive J=ψ cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean B hadron rapidity y ¼ 1.7 in 510 GeV p þ p collisions, is 3.63+1.92 −1.70 μb. It is consistent with the fixed-order-next-toleading-logarithm calculations.
J/ψ and ψ(2S) production at forward rapidity in p+p collisions at √s=510 GeV
No full textThe PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section, mean transverse momentum, mean transverse momentum squared of inclusive J/ψ, and cross section ratio of ψ(2S) to J/ψ at forward rapidity in p+p collisions at √s=510 GeV via the dimuon decay channel. Comparison is made to inclusive J/ψ cross sections measured at √s=200 GeV and 2.76–13 TeV. The result is also compared to leading-order nonrelativistic QCD calculations coupled to a color-glass-condensate description of the low-x gluons in the proton at low transverse momentum (pT) and to next-to-leading order nonrelativistic QCD calculations for the rest of the pT range. These calculations overestimate the data at low pT. While consistent with the data within uncertainties above ≈3 GeV/c, the calculations are systematically below the data. The total cross section times the branching ratio is BR dσJ/ψpp/dy(1.2\u3c|y|\u3c2.2,
Polarization and cross section of midrapidity J/ψ production in p+p collisions at √s=510 GeV
No full textThe PHENIX experiment has measured the spin alignment for inclusive J/ψ→e+e− decays in proton-proton collisions at √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.
Measurement of charm and bottom production from semileptonic hadron decays in p + p collisions at √ s = 200 GeV
No full textMeasurements of the differential production of electrons from open-heavy-flavor hadrons with charm- and bottom-quark content in p+p collisions at √s=200 GeV are presented. The measurements proceed through displaced-vertex analyses of electron tracks from the semileptonic decay of charm and bottom hadrons using the PHENIX silicon-vertex detector. The relative contribution of electrons from bottom decays to inclusive heavy-flavor-electron production is found to be consistent with fixed-order-plus-next-to-leading-log perturbative-QCD calculations within experimental and theoretical uncertainties. These new measurements in p+p collisions provide a precision baseline for comparable forthcoming measurements in A+A collisions
Production of b¯b at forward rapidity in p+p collisions at √s=510 GeV
No full textThe cross section of bottom quark-antiquark (b¯b) production in p+p collisions at √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\u3c|y|\u3c2.2). The b¯b signal is extracted from like-sign dimuons by utilizing the unique properties of neutral B meson oscillation. We report a differential cross section of dσb¯b→μ±μ±/dy=0.16±0.01 (stat)±0.02 (syst)±0.02 (global) nb for like-sign muons in the rapidity and pT ranges 1.2\u3c|y|\u3c2.2 and pT\u3e1 GeV/c, and dimuon mass of 5–10 GeV/c2. The extrapolated total cross section at this energy for b¯b production is 13.1±0.6 (stat)±1.5 (syst)±2.7 (global) μb. 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 decays and their pT distributions are compared to distributions generated using ps pythia6, which includes next-to-leading order processes. The azimuthal correlations and pair pT 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
Measurements of μμ pairs from open heavy flavor and Drell-Yan in p + p collisions at ffiffi s p = 200 GeV
No full textPHENIX reports differential cross sections of μμ pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in p+p collisions at √s=200 GeV at forward and backward rapidity (1.2\u3c|η|\u3c2.2). The μμ pairs from c¯c, b¯b, and Drell-Yan are separated using a template fit to unlike- and like-sign muon pair spectra in mass and pT. The azimuthal opening angle correlation between the muons from c¯c and b¯b decays and the pair-pT distributions are compared to distributions generated using pythia and powheg models, which both include next-to-leading order processes. The measured distributions for pairs from c¯c are consistent with pythia calculations. The c¯c data present narrower azimuthal correlations and softer pT distributions compared to distributions generated from powheg. The b¯b data are well described by both models. The extrapolated total cross section for bottom production is 3.75±0.24(stat)±0.350.50(syst)±0.45(global) [μb], which is consistent with previous measurements at the Relativistic Heavy Ion Collider in the same system at the same collision energy and is approximately a factor of 2 higher than the central value calculated with theoretical models. The measured Drell-Yan cross section is in good agreement with next-to-leading-order quantum-chromodynamics calculations
Transverse single spin asymmetries of forward neutrons in p + p , p + Al , and p + Au collisions at √ s N N = 200 GeV as a function of transverse and longitudinal momenta
No full textIn 2015 the PHENIX collaboration at the Relativistic Heavy Ion Collider recorded p+p, p+Al, and p+Au collision data at center of mass energies of √sNN=200 GeV with the proton beam(s) transversely polarized. At very forward rapidities η\u3e6.8 relative to the polarized proton beam, neutrons were detected either inclusively or in (anti)correlation with detector activity related to hard collisions. The resulting single spin asymmetries, that were previously reported, have now been extracted as a function of the transverse momentum of the neutron as well as its longitudinal momentum fraction xF. The explicit kinematic dependence, combined with the correlation information allows for a closer look at the interplay of different mechanisms suggested to describe these asymmetries, such as hadronic interactions or electromagnetic interactions in ultraperipheral collisions, UPC. Events that are correlated with a hard collision indeed display a mostly negative asymmetry that increases in magnitude as a function of transverse momentum with only little dependence on xF. In contrast, events that are not likely to have emerged from a hard collision display positive asymmetries for the nuclear collisions with a kinematic dependence that resembles that of a UPC based model. Because the UPC interaction depends strongly on the charge of the nucleus, those effects are very small for p+p collisions, moderate for p+Al collisions, and large for p+Au collisions
Kinematic dependence of azimuthal anisotropies in p + Au , d + Au , and 3 He + Au at √ s N N = 200 GeV
No full textThere is strong evidence for the formation of small droplets of quark-gluon plasma in p/d/3He+Au collisions at the Relativistic Heavy Ion Collider (RHIC) and in p+p/Pb collisions at the Large Hadron Collider. In particular, the analysis of data at RHIC for different geometries obtained by varying the projectile size and shape has proved insightful. In the present analysis, we find excellent agreement with the previously published PHENIX at RHIC results on elliptical and triangular flow with an independent analysis via the two-particle correlation method, which has quite different systematic uncertainties and an independent code base. In addition, the results are extended to other detector combinations with different kinematic (pseudorapidity) coverage. These results provide additional constraints on contributions from nonflow and longitudinal decorrelations
Transverse single-spin asymmetries of midrapidity π 0 and η mesons in polarized p + p collisions at √ s = 200 GeV
No full textWe present a measurement of the transverse single-spin asymmetry for π0 and η mesons in p↑+p collisions in the pseudorapidity range |η|\u3c0.35 and at a center-of-mass energy of 200 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. In comparison with previous measurements in this kinematic region, these results have factor-of-3-smaller uncertainties. As hadrons, π0 and η mesons are sensitive to both initial- and final-state nonperturbative effects for a mix of parton flavors. Comparisons of the differences in their transverse single-spin asymmetries have the potential to disentangle the possible effects of strangeness, isospin, or mass. These results can constrain the twist-3 trigluon collinear correlation function as well as the gluon Sivers function
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