Cross section and transverse single-spin asymmetry of eta mesons in p up arrow plus p collisions at root s=200 GeV at forward rapidity

We present a measurement of the cross section and transverse single-spin asymmetry (AN) for. mesons at large pseudorapidity from root s = 200 GeV p up arrow + p collisions. The measured cross section for 0.5 \u3c p(T) \u3c 5.0 GeV/c and 3.0 \u3c vertical bar eta vertical bar \u3c 3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries A(N) have been measured as a function of Feynman-x (x(F)) from 0.2 \u3c vertical bar x(F)vertical bar \u3c 0.7, as well as transverse momentum (p(T)) from 1.0 \u3c p(T) \u3c 4.5 GeV/c. The asymmetry averaged over positive x(F) is \u3c A(N)\u3e = 0.061 +/- 0.014. The results are consistent with prior transverse single-spin measurements of forward eta and pi(0) mesons at various energies in overlapping x(F) ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p up arrow + p collisions

phi meson production in d plus Au collisions at root s(NN)=200 GeV

The PHENIX Collaboration has measured phi meson production in d + Au collisions at root s(NN) = 200 GeV using the dimuon and dielectron decay channels. The phi meson is measured in the forward (backward) d-going (Au-going) direction, 1.2 \u3c y \u3c 2.2 (-2.2 \u3c y \u3c -1.2) in the transverse-momentum (pT) range from 1-7 GeV/c and at midrapidity vertical bar y vertical bar \u3c 0.35 in the p(T) range below 7 GeV/c. The phi meson invariant yields and nuclear-modification factors as a function of p(T), rapidity, and centrality are reported. An enhancement of phi meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p + p collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects

Measurement of higher cumulants of net-charge multiplicity distributions in Au plus Au collisions at root s(NN)=7.7-200 GeV

We report the measurement of cumulants (C-n,n = 1, ..., 4) of the net-charge distributions measured within pseudorapidity (vertical bar eta vertical bar \u3c 0.35) in Au + Au collisions at root s(NN) = 7.7-200 GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider. The ratios of cumulants (e.g., C-1/C-2, C-3/C-1) of the net-charge distributions, which can be related to volume independent susceptibility ratios, are studied as a function of centrality and energy. These quantities are important to understand the quantum-chromodynamics phase diagram and possible existence of a critical end point. The measured values are very well described by expectation from negative binomial distributions. We do not observe any nonmonotonic behavior in the ratios of the cumulants as a function of collision energy. The measured values of C-1/C-2 and C-3/C-1 can be directly compared to lattice quantum-chromodynamics calculations and thus allow extraction of both the chemical freeze-out temperature and the baryon chemical potential at each center-of-mass energy. The extracted baryon chemical potentials are in excellent agreement with a thermal-statistical analysis model

Low-mass vector-meson production at forward rapidity in p plus p collisions at root s=200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson, omega, rho, and phi, production through the dimuon decay channel at forward rapidity (1.2 \u3c vertical bar y vertical bar \u3c 2.2) in p + p collisions at root s = 200 GeV. The differential cross sections for these mesons are measured as a function of both p(T) and rapidity. We also report the integrated differential cross sections over 1 \u3c p(T) \u3c 7 GeV/c and 1.2 \u3c vertical bar y vertical bar \u3c 2.2: d sigma/dy(omega + rho rho -\u3e mu mu) = 80 +/- 6(stat) +/- 12(syst)nb and d sigma/dy(phi -\u3e mu mu) = 27 +/- 3(stat) +/- 4(syst)nb. These results are compared with midrapidity measurements and calculations

Centrality-Dependent Modification of Jet-Production Rates in Deuteron-Gold Collisions at root s(NN)=200 GeV

Jet production rates are measured in p + p and d + Au collisions at root s(NN) = 200 GeV recorded in 2008 with the PHENIX detector at the Relativistic Heavy Ion Collider. Jets are reconstructed using the R = 0.3 anti-k(t) algorithm from energy deposits in the electromagnetic calorimeter and charged tracks in multiwire proportional chambers, and the jet transverse momentum (p(T)) spectra are corrected for the detector response. Spectra are reported for jets with 12 \u3c p(T) \u3c 50 GeV/c, within a pseudorapidity acceptance of vertical bar eta vertical bar \u3c 0.3. The nuclear-modification factor (R-dAu) values for 0%-100% d + Au events are found to be consistent with unity, constraining the role of initial state effects on jet production. However, the centrality-selected RdAu values and central-to-peripheral ratios (R-CP) show large, p(T)-dependent deviations from unity, challenging the conventional models that relate hard-process rates and soft-particle production in collisions involving nuclei

Single electron yields from semileptonic charm and bottom hadron decays in Au plus Au collisions at root s(NN)=200 GeV

The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open heavy flavor production in minimum bias Au + Au collisions at root s(NN) = 200 GeV via the yields of electrons from semileptonic decays of charm and bottom hadrons. Previous heavy flavor electron measurements indicated substantial modification in the momentum distribution of the parent heavy quarks owing to the quark-gluon plasma created in these collisions. For the first time, using the PHENIX silicon vertex detector to measure precision displaced tracking, the relative contributions from charm and bottom hadrons to these electrons as a function of transverse momentum are measured in Au + Au collisions. We compare the fraction of electrons from bottom hadrons to previously published results extracted from electron-hadron correlations in p + p collisions at root s(NN) = 200 GeV and find the fractions to be similar within the large uncertainties on both measurements for p(T) \u3e 4 GeV/c. We use the bottom electron fractions in Au + Au and p + p along with the previously measured heavy flavor electron R-AA to calculate the R-AA for electrons from charm and bottom hadron decays separately. We find that electrons from bottom hadron decays are less suppressed than those from charm for the region 3 \u3c p(T) \u3c 4 GeV/c

Dielectron production in Au plus Au collisions at root s(NN)=200 GeV

We present measurements of e(+)e-production at midrapidity in Au + Au collisions at root s(NN) = 200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (m(ee) \u3c 5 GeV/c(2)) and pair transverse momentum (p(T) \u3c 5 GeV/c) for minimum bias and for five centrality classes. The e(+)e(-) yield is compared to the expectations from known sources. In the low-mass region (m(ee) = 0.30-0.76 GeV/c(2)) there is an enhancement that increases with centrality and is distributed over the entire pair p(T) range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to 2.3 +/- 0.4(stat) +/- 0.4(syst) +/- 0.2(model) or to 1.7 +/- 0.3(stat) +/- 0.3(syst) +/- 0.2(model) for minimum bias collisions when the open heavy-flavor contribution is calculated with PYTHIA or MC@NLO, respectively. The inclusive mass and p(T) distributions, as well as the centrality dependence, are well reproduced by model calculations where the enhancement mainly originates from the melting of the rho meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region (m(ee) = 1.2-2.8 GeV/c(2)), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons

Measurement of emission-angle anisotropy via long-range angular correlations with high-pT hadrons in d + Au and p + p collisions at √sNN = 200 GeV

We present measurements of two-particle angular correlations between high-transverse-momentum (2 \u3c pT \u3c 11 GeV/c) pi(0) observed at midrapidity (|eta| \u3c 0.35) and particles produced either at forward (3.1 \u3c eta \u3c 3.9) or backward (-3.7 \u3c eta \u3c -3.1) rapidity in d + Au and p + p collisions at root s(NN) = 200 GeV. The azimuthal angle correlations for particle pairs with this large rapidity gap in the Au-going direction exhibit a characteristic structure that persists up to pT approximate to 6 GeV/c and which strongly depends on collision centrality, which is a similar characteristic to the hydrodynamical particle flow in A + A collisions. The structure is absent in the d-going direction as well as in p + p collisions, in the transverse-momentum range studied. The results indicate that the structure is shifted in the Au-going direction toward more central collisions, similar to the charged-particle pseudorapidity distributions

Measurement of parity-violating spin asymmetries in W-+/- production at midrapidity in longitudinally polarized p plus p collisions

We present midrapidity measurements from the PHENIX experiment of large parity-violating single-spin asymmetries of high transverse momentum electrons and positrons from W-+/-/Z decays, produced in longitudinally polarized p + p collisions at center of mass energies of root s = 500 and 510 GeV. These asymmetries allow direct access to the antiquark polarized parton distribution functions due to the parity-violating nature of the W-boson coupling to quarks and antiquarks. The results presented are based on data collected in 2011, 2012, and 2013 with an integrated luminosity of 240 pb(-1), which exceeds previous PHENIX published results by a factor of more than 27. These high Q(2) data probe the parton structure of the proton at W mass scale and provide an important addition to our understanding of the antiquark parton helicity distribution functions at an intermediate Bjorken x value of roughly M-W / root s = 0.16