We report $e^\pm-\mu^\mp$ pair yield from charm decay measured between midrapidity electrons ($|\eta|<0.35$ and $p_T>0.5$ GeV/$c$) and forward rapidity muons ($1.4<\eta<2.1$ and $p_T>1.0$ GeV/$c$) as a function of $\Delta\phi$ in both $p$$+$$p$ and in $d$+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Comparing the $p$$+$$p$ results with several different models, we find the results are consistent with a total charm cross section $\sigma_{c\bar{c}} =$ 538 $\pm$ 46 (stat) $\pm$ 197 (data syst) $\pm$ 174 (model syst) $\mu$b. These generators also indicate that the back-to-back peak at $\Delta\phi = \pi$ is dominantly from the leading order contributions (gluon fusion), while higher order processes (flavor excitation and gluon splitting) contribute to the yield at all $\Delta\phi$. We observe a suppression in the pair yield per collision in $d$+Au. We find the pair yield suppression factor for $2.7<\Delta\phi<3.2$ rad is $J_{dA}$ = 0.433 $\pm$ 0.087 (stat) $\pm$ 0.135 (syst), indicating cold nuclear matter modification of $c\bar{c}$ pairs.
The fully-corrected like-sign-subtracted heavy flavor $e$-$\mu$ pair yield in $p$+$p$.
The fully corrected like-sign-subtracted heavy flavor $e$-$\mu$ pair yield in $d$+Au.
$J_{dA}$ plotted as a function of $\Delta\phi$.
The three Upsilon states, Upsilon(1S+2S+3S), are measured in d+Au and p+p collisions at sqrt(s_NN)=200 GeV and rapidities 1.2<|y|<2.2 by the PHENIX experiment at the Relativistic Heavy-Ion Collider. Cross sections for the inclusive Upsilon(1S+2S+3S) production are obtained. The inclusive yields per binary collision for d+Au collisions relative to those in p+p collisions (R_dAu) are found to be 0.62 +/- 0.26 (stat) +/- 0.13 (syst) in the gold-going direction and 0.91 +/- 0.33 (stat) +/- 0.16 (syst) in the deuteron-going direction. The measured results are compared to a nuclear-shadowing model, EPS09 [JHEP 04, 065 (2009)], combined with a final-state breakup cross section, sigma_br, and compared to lower energy p+A results. We also compare the results to the PHENIX J/psi results [Phys. Rev. Lett. 107, 142301 (2011)]. The rapidity dependence of the observed Upsilon suppression is consistent with lower energy p+A measurements.
$\Upsilon$ invariant yields and cross sections of $p$+$p$ and $d$+Au collisions.
We report on the first measurement of double-spin asymmetry, A_LL, of electrons from the decays of hadrons containing heavy flavor in longitudinally polarized p+p collisions at sqrt(s)=200 GeV for p_T= 0.5 to 3.0 GeV/c. The asymmetry was measured at mid-rapidity (|eta|<0.35) with the PHENIX detector at the Relativistic Heavy Ion Collider. The measured asymmetries are consistent with zero within the statistical errors. We obtained a constraint for the polarized gluon distribution in the proton of |Delta g/g(log{_10}x= -1.6^+0.5_-0.4, {mu}=m_T^c)|^2 < 0.033 (1 sigma), based on a leading-order perturbative-quantum-chromodynamics model, using the measured asymmetry.
Invariant differential cross sections of electrons from heavy-flavor decays.
Double-spin asymmetry of the heavy flavor electron production.
We present measurements of the J/psi invariant yields in sqrt(s_NN)=39 and 62.4 GeV Au+Au collisions at forward rapidity (1.2<|y|<2.2). Invariant yields are presented as a function of both collision centrality and transverse momentum. Nuclear modifications are obtained for central relative to peripheral Au+Au collisions (R_CP) and for various centrality selections in Au+Au relative to scaled p+p cross sections obtained from other measurements (R_AA). The observed suppression patterns at 39 and 62.4 GeV are quite similar to those previously measured at 200 GeV. This similar suppression presents a challenge to theoretical models that contain various competing mechanisms with different energy dependencies, some of which cause suppression and others enhancement.
Estimates used for the 39- and 62.4-GeV $J/\psi$ $p$+$p$ cross sections along with their uncertainties.
$J/\psi$ invariant yields are shown for Au+Au collisions at 39 and 62.4 GeV as a function of the number of participating nucleons.
$J/\psi$ invariant yields are shown for Au+Au collisions at 39 and 62.4 GeV as a function of the number of participating nucleons.
Background: Heavy-flavor production in p+p collisions tests perturbative-quantum-chromodynamics (pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative to binary-collision scaling from p+p results, quantified with the nuclear-modification factor (R_AA), provides information on both cold- and hot-nuclear-matter effects. Purpose: Determine transverse-momentum, pt, spectra and the corresponding R_AA for muons from heavy-flavor mesons decay in p+p and Cu+Cu collisions at sqrt(s_NN)=200 GeV and y=1.65. Method: Results are obtained using the semi-leptonic decay of heavy-flavor mesons into negative muons. The PHENIX muon-arm spectrometers measure the p_T spectra of inclusive muon candidates. Backgrounds, primarily due to light hadrons, are determined with a Monte-Carlo calculation using a set of input hadron distributions tuned to match measured-hadron distributions in the same detector and statistically subtracted. Results: The charm-production cross section in p+p collisions at sqrt{s}=200 GeV, integrated over pt and in the rapidity range 1.4<y<1.9 is found to be dsigma_ccbar/dy = 0.139 +/- 0.029 (stat) ^{+0.051}_{-0.058} (syst) mb. This result is consistent with calculations and with expectations based on the corresponding midrapidity charm-production cross section measured earlier by PHENIX. The R_AA for heavy-flavor muons in Cu+Cu collisions is measured in three centrality intervals for 1<pt<4 GeV/c. Suppression relative to binary-collision scaling (R_AA<1) increases with centrality. Conclusions: Within experimental and theoretical uncertainties, the measured heavy-flavor yield in p+p collisions is consistent with state-of-the-art pQCD calculations. Suppression in central Cu+Cu collisions suggests the presence of significant cold-nuclear-matter effects and final-state energy loss.
Production cross section of negative muons from heavy-flavor mesons decay as a function of $p_T$ in $p$+$p$ collisions at $\sqrt{s}=200$ GeV.
Invariant production yields of negative muons from heavy-flavor-mesons decay as a function $p_T$ in Cu+Cu collisions for three different centrality intervals (40-94%, 20-40%, and 0-20%), scaled by powers of ten for clarity. The solid line associated to each set of points corresponds to a fit to the $p$+$p$ invariant yield distribution described in the text, scaled by the appropriate number of binary collisions $N_{coll}$ when comparing to the Cu+Cu measurements.
Invariant production yields of negative muons from heavy-flavor-mesons decay as a function $p_T$ in $p$+$p$ collisions at $\sqrt{s}=200$ GeV. The solid line associated to each set of points corresponds to a fit to the $p$+$p$ invariant yield distribution described in the text, scaled by the appropriate number of binary collisions $N_{coll}$ when comparing to the Cu+Cu measurements.
We report on charmonium measurements [J/psi(1S), psi'(2S), and chi_c(1P)] in p+p collisions at sqrt(s)=200 GeV. We find that the fraction of J/psi coming from the feed-down decay of psi' and chi_c in the midrapidity region ($|\eta|<0.35$) is 9.6+/-2.4% and 32+/-9%, respectively. We also report new, higher statistics p_T and rapidity dependencies of the J/psi yield via dielectron decay in the same midrapidity range and at forward rapidity (1.2<|eta|<2.4) via dimuon decay. These results are compared with measurements from other experiments and discussed in the context of current charmonium production models.
Foreground, background counts in the $J/\psi$ mass region, and the signal count.
Foreground, background counts in the $J/\psi$ mass region, and the signal count.
$\psi^{\prime}(J/\psi)$ dielectron yield ratio measured at $|y|$ < 0.35 followed by point-to-point uncorrelated (uncorr.) (statistical and uncorrelated systematic uncertainties) and correlated systematic (corr.) uncertainties.
Back-to-back hadron pair yields in d+Au and p+p collisions at sqrt(s_NN)=200 GeV were measured with the PHENIX detector at the Relativistic Heavy Ion Collider. Rapidity separated hadron pairs were detected with the trigger hadron at pseudorapidity |eta|<0.35 and the associated hadron at forward rapidity (deuteron direction, 3.0<eta<3.8). Pairs were also detected with both hadrons measured at forward rapidity; in this case the yield of back-to-back hadron pairs in d+Au collisions with small impact parameters is observed to be suppressed by a factor of 10 relative to p+p collisions. The kinematics of these pairs is expected to probe partons in the Au nucleus with low fraction x of the nucleon momenta, where the gluon densities rise sharply. The observed suppression as a function of nuclear thickness, p_T, and eta points to cold nuclear matter effects arising at high parton densities.
$J_{dA}$ versus $x^{frag}_{Au}$ for $d$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for different centrality classes.
$J_{dA}$ versus $x^{frag}_{Au}$ for $d$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for different centrality classes.
$J_{dA}$ versus $x^{frag}_{Au}$ for $d$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for different centrality classes.
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured omega meson production via leptonic and hadronic decay channels in p+p, d+Au, Cu+Cu, and Au+Au collisions at sqrt(s_NN) = 200 GeV. The invariant transverse momentum spectra measured in different decay modes give consistent results. Measurements in the hadronic decay channel in Cu+Cu and Au+Au collisions show that omega production has a suppression pattern at high transverse momentum, similar to that of pi^0 and eta in central collisions, but no suppression is observed in peripheral collisions. The nuclear modification factors, R_AA, are consistent in Cu+Cu and Au+Au collisions at similar numbers of participant nucleons.
Invariant transverse momentum spectra of $\omega$ production in $p$+$p$ and $d$+Au collisions at $\sqrt{s}$=200 GeV.
Invariant transverse momentum spectra of $\omega$ production in $p$+$p$ and $d$+Au collisions at $\sqrt{s}$=200 GeV.
Invariant transverse momentum spectra of $\omega$ production in $p$+$p$ and $d$+Au collisions at $\sqrt{s}$=200 GeV.
We report on event structure and double helicity asymmetry ($A_LL$) of jet production in longitudinally polarized p+p collisions at $\sqrt{s}$=200 GeV. Photons and charged particles were measured at midrapidity $|\eta| < 0.35$ with the requirement of a high-momentum ($>2$ GeV/$c$) photon in each event. Measured event structure is compared with {\sc pythia} and {\sc geant} simulations. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet $A_{LL}$, photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster $p_T$ sum ($p_T^{\rm reco}$). The effect of detector response and the underlying events on $p_T^{\rm reco}$ was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the NLO pQCD jet production cross section. For $4 < p_T^{\rm reco} < 12$ GeV/$c$ with an average beam polarization of $< P > = 49%$ we measured $A_{LL} = -0.0014 \pm 0.0037^{\rm stat}$ at the lowest $p_T^{\rm reco}$ bin (4-5 GeV/$c$) and $-0.0181 \pm 0.0282^{\rm stat}$ at the highest $p_T^{\rm reco}$ bin (10-12 GeV/$c$) with a beam polarization scale error of 9.4% and a $\pT$ scale error of 10%. Jets in the measured $p_T^{\rm reco}$ range arise primarily from hard-scattered gluons with momentum fraction $0.02 < x < 0.3$ according to {\sc pythia}. The measured $A_{LL}$ is compared with predictions that assume various $\Delta G(x)$ distributions based on the GRSV parameterization. The present result imposes the limit $-1.1 < \int_{0.02}^{0.3}dx \Delta G(x, \mu^2 = 1 {\rm GeV}^2) < 0.4$ at 95% confidence level or $\int_{0.02}^{0.3}dx \Delta G(x, \mu^2 = 1 {\rm GeV}^2) < 0.5$ at 99% confidence level.
The relative yields of $q$+$q$, $q$+$g$, and $g$+$g$ subprocesses in the PYTHIA+GEANT simulation.
The correction factor $\epsilon^j_{trig+acc}$ for high-$p_T$ photon trigger efficiency and acceptance effect.
Reconstructed-jet $A_{LL}$ as a function of $p_T^{reco}$.
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the invariant differential cross section for production of K^0_S , \omega, \eta prime, and \phi mesons in p + p collisions at = 200 GeV. Measurements \omega and \phi production in different decay channels give consistent results. New results for the \phi are in agreement with previously published data and extend the measured pT coverage. The spectral shapes of all hadron transverse momentum distributions measured by PHENIX are well described by a Tsallis distribution functional form with only two parameters, n and T, determining the high-pT and characterizing the low-pT regions of the spectra, respectively. The values of these parameters are very similar for all analyzed meson spectra, but with a lower parameter T extracted for protons. The integrated invariant cross sections calculated from the fitted distributions are found to be consistent with existing measurements and with statistical model predictions.
Parameters of the Tsallis fit with Eq. 8 in the paper with all parameters free to vary. Cross sections are in $\mu$b for $J/\psi$ and $\psi^{\prime}$ and in mb for all other particles.
Parameters of the power law fit with Eq. 3 in the paper. Units of $A$ are mb(GeV/$c$)$^{\upsilon + 2}$.
Constant and linear fits to the power law and Tsallis fit parameters. The last column (Prob.) gives the probability estimated by the $\chi^2$/$n.d.f.$ of the fit.
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