Distributions of event-by-event fluctuations of the mean transverse momentum and mean transverse energy near mid-rapidity have been measured in Au+Au collisions at sqrt(s_NN) = 130 GeV at RHIC. By comparing the distributions to what is expected for statistically independent particle emission, the magnitude of non-statistical fluctuations in mean transverse momentum is determined to be consistent with zero. Also, no significant non-random fluctuations in mean transverse energy are observed. By constructing a fluctuation model with two event classes that preserve the mean and variance of the semi-inclusive p_T or e_T spectra, we exclude a region of fluctuations in sqrt(s_NN) = 130 GeV Au+Au collisions.
The $N_{tracks}$ distribution for the $0-10\%$ centrality class (data points) compared to the $N_{mix}$ distribution from the mixed event sample (curve).
The $M_{p_T}$ distributions for four different centrality classes. The curves are the random baseline mixed event distributions.
The residual distribution between the data and mixed event $M_{p_T}$ in units of standard deviations for all centrality classes. The total ${\chi}^2$ and the number of degrees of freedom for the $0-5\%$, $0-10\%$, $10-20\%$, $20-30\%$ centrality classes are 89.0/39, 155.7/40,163.3/47, and 218.4/61, respectively.
The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment $(g-2)_\mu$ deviates from SM calculations by 3.6$\sigma$. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, $U$, in $\pi^0,\eta \rightarrow \gamma e^+e^-$ decays and obtained upper limits of $\mathcal{O}(2\times10^{-6})$ on $U$-$\gamma$ mixing at 90% CL for the mass range $30<m_U<90$ MeV/$c^2$. Combined with other experimental limits, the remaining region in the $U$-$\gamma$ mixing parameter space that can explain the $(g-2)_\mu$ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of $29<m_U<32$ MeV/$c^2$ remaining.
The experimental sensitivity and observed limit on the number of dark photon candidates as a function of the assumed dark photon mass.
The experimental sensitivity and observed limit on the number of dark photon candidates as a function of the assumed dark photon mass.
The experimental sensitivity and observed limit on the number of dark photon candidates as a function of the assumed dark photon mass.
Dihadron and isolated direct photon-hadron angular correlations are measured in $p$$+$$p$ collisions at $\sqrt{s}=510$ 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 $p_{\rm out}$ 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 ($p_T^{\rm trig}$). The Gaussian widths and root mean square of $p_{\rm out}$ are reported as a function of the interaction hard scale $p_T^{\rm trig}$ to investigate possible transverse-momentum-dependent evolution differences between the $\pi^0$-h$^\pm$ and direct photon-h$^\pm$ correlations and factorization breaking effects. The widths are found to decrease with $p_T^{\rm trig}$, 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.
Per-trigger yield of charged hadrons shown as a function of the azimuthal angle between the $\pi^0$ trigger particle and associated charged hadron.
Per-trigger yield of charged hadrons shown as a function of the azimuthal angle between the direct photon trigger particle and associated charged hadron.
$\pi^0$-h$^{\pm}$ $\sqrt{\langle p^2_{out} \rangle}$ values from fits to the $\Delta \phi$ correlations.
The transverse momentum dependence of the azimuthal anisotropy parameter v_2, the second harmonic of the azimuthal distribution, for electrons at mid-rapidity (|eta| < 0.35) has been measured with the PHENIX detector in Au+Au collisions at sqrt(s_NN) = 200 GeV. The measurement was made with respect to the reaction plane defined at high rapidities (|eta| = 3.1 -- 3.9). From the result we have measured the v_2 of electrons from heavy flavor decay after subtraction of the v_2 of electrons from other sources such as photon conversions and Dalitz decay from light neutral mesons. We observe a non-zero single electron v_2 with a 90% confidence level in the intermediate p_T region.
Transverse momentum dependence of inclusive electron $v_2$ and heavy quark electron $v_2$.
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.
We report on the yield of protons and anti-protons, as a function of centrality and transverse momentum, in Au+Au collisions at sqrt(s_NN) = 200 GeV measured at mid-rapidity by the PHENIX experiment at RHIC. In central collisions at intermediate transverse momenta (1.5 < p_T < 4.5 GeV/c) a significant fraction of all produced particles are protons and anti-protons. They show a centrality-scaling behavior different from that of pions. The p-bar/pion and p/pion ratios are enhanced compared to peripheral Au+Au, p+p, and electron+positron collisions. This enhancement is limited to p_T < 5 GeV/c as deduced from the ratio of charged hadrons to pi^0 measured in the range 1.5 < p_T < 9 GeV/c.
$p$/$\pi^+$ and $p$/$\pi^-$ ratios for central (0-10%) mid-central (20-30%) and peripheral (60-92%) Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
$p$/$\pi^-$ and $p$/$\pi^0$ ratios for central (0-10%) mid-central (20-30%) and peripheral (60-92%) Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
$p$ and $\bar{p}$ invariant yields scaled by $N_{coll}$. Error bars are statistical. Systematic errors on $N_{coll}$ range from ~ 10% for central to ~ 28% for 60-92% centrality. Multiplicity dependent normalization errors are ~3%.
Transverse momentum spectra of electrons from Au+Au collisions at sqrt(s_NN) = 130 GeV have been measured by the PHENIX experiment at RHIC. The spectra show an excess above the background from photon conversions and light hadron decays. The electron signal is consistent with that expected from semi-leptonic decays of charm. The yield of the electron signal dN_e/dy for p_T > 0.8 GeV/c is 0.025 +/- 0.004 (stat.) +/- 0.010 (sys.) in central collisions, and the corresponding charm cross section is 380 +/- 60 (stat.) +/- 200 (sys.) micro barns per binary nucleon-nucleon collision.
Transverse momentum spectra of electrons in PHENIX from Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV.
Transverse momentum spectra of electrons in PHENIX from Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV.
Transverse momentum spectra of electrons in PHENIX from Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV. The upper limit for 1.9 GeV/$c$ is 4.10224e-05.
The energy dependence of the single-transverse-spin asymmetry, A_N, and the cross section for neutron production at very forward angles were measured in the PHENIX experiment at RHIC for polarized p+p collisions at sqrt(s)=200 GeV. The neutrons were observed in forward detectors covering an angular range of up to 2.2 mrad. We report results for neutrons with momentum fraction of x_F=0.45 to 1.0. The energy dependence of the measured cross sections were consistent with x_F scaling, compared to measurements by an ISR experiment which measured neutron production in unpolarized p+p collisions at sqrt(s)=30.6--62.7 GeV. The cross sections for large x_F neutron production for p+p collisions, as well as those in e+p collisions measured at HERA, are described by a pion exchange mechanism. The observed forward neutron asymmetries were large, reaching A_N=-0.08+/-0.02 for x_F=0.8; the measured backward asymmetries, for negative x_F, were consistent with zero. The observed asymmetry for forward neutron production is discussed within the pion exchange framework, with interference between the spin-flip amplitude due to the pion exchange and nonflip amplitudes from all Reggeon exchanges. Within the pion exchange description, the measured neutron asymmetry is sensitive to the contribution of other Reggeon exchanges even for small amplitudes.
The cross section results for forward neutron production in $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV are shown. Two different forms, exponential and Gaussian, were used for the $p_T$ distribution. The integrated $p_T$ region for each bin is 0 < $p_T$ < 0.11$x_F$ GeV/$c$.
The $x_F$ dependence of $A_N$ for neutron production in the ZDC trigger sample.
The $x_F$ dependence of $A_N$ for neutron production for the ZDC$\otimes$BBC trigger sample.
Direct photons have been measured in sqrt(s_NN)=200 GeV d+Au collisions at midrapidity. A wide p_T range is covered by measurements of nearly-real virtual photons (1<p_T<6 GeV/c) and real photons (5<p_T<16 GeV/c). The invariant yield of the direct photons in d+Au collisions over the scaled p+p cross section is consistent with unity. Theoretical calculations assuming standard cold nuclear matter effects describe the data well for the entire p_T range. This indicates that the large enhancement of direct photons observed in Au+Au collisions for 1.0<p_T<2.5 GeV/c is due to a source other than the initial-state nuclear effects.
Direct photon fraction. The direct-photon fractions from the virtual-photon analysis as a function of $p_{T}$ in $p+p$ (MB) [1] collisions. The values in the table are equal to this mean value. The statistical and systematic uncertainties are shown by the bars and bands, respectively. The curves show expectations from a NLO pQCD calculation [17, 18] with different cutoff mass scales: (solid) $\mu$ = 0.5 $p_{T}$ , (dash) $\mu$ = 1.0 $p_{T}$ , and (dash-dot) $\mu$ = 2.0 $p_{T}$.
Direct photon fraction. The direct-photon fractions from the virtual-photon analysis as a function of $p_{T}$ in $d$+Au (MB) [1] collisions. The values in the table are equal to this mean value. The statistical and systematic uncertainties are shown by the bars and bands, respectively. The curves show expectations from a NLO pQCD calculation [17, 18] with different cutoff mass scales: (solid) $\mu$ = 0.5 $p_{T}$ , (dash) $\mu$ = 1.0 $p_{T}$ , and (dash-dot) $\mu$ = 2.0 $p_{T}$.
Direct photon cross section. (a) The invariant cross sections of the direct photon in $p+p$ [3, 4] and $d$+Au collisions. The $p+p$ fit result with the empirical parameterization described in the text is shown as well as NLO pQCD calculations, and the scaled $p+p$ fit is compared with the $d$+Au data. The closed and open symbols show the results from the virtual photon and $\pi_{0}$-tagging methods, respectively. The asterisk symbols show the result from the statistical subtraction method for $d$+Au data, overlapping with the virtual photon result in 3 < $p_{T}$ < 5 GeV/c. The values in the table are equal to this mean value. The bars and bands represent the point-to-point (ptp.) and $p_{T}$-correlated (cor.) uncertainties, respectively. (b) The $p+p$ data over the fit. The uncertainties of the fit due to both point-to-point (ptp.) and pT -correlated uncertainties of the data are summed quadratically, and the sum is shown as dotted lines. The NLO pQCD calculations divided by the fit are also shown.
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured 2nd and 3rd order Fourier coefficients of the azimuthal distributions of direct photons emitted at midrapidity in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV for various collision centralities. Combining two different analysis techniques, results were obtained in the transverse momentum range of $0.4<p_{T}<4.0$ GeV/$c$. At low $p_T$ the second-order coefficients, $v_2$, are similar to the ones observed in hadrons. Third order coefficients, $v_3$, are nonzero and almost independent of centrality. These new results on $v_2$ and $v_3$, combined with previously published results on yields, are compared to model calculations that provide yields and asymmetries in the same framework. Those models are challenged to explain simultaneously the observed large yield and large azimuthal anisotropies.
Direct photon $v_2$ and $v_3$ at midrapidity ($|\eta|$ < 0.35), for different centralities, measured with the conversion method. The event plane was determined with the reaction plane detector (1 < $|\eta|$ < 2.8).
Direct photon $v_2$ and $v_3$ at midrapidity ($|\eta|$ < 0.35), for different centralities, measured with the calorimeter method. The event plane was determined with the reaction plane detector (1 < $|\eta|$ < 2.8).
Differential measurements of the elliptic (v_2) and hexadecapole (v_4) Fourier flow coefficients are reported for charged hadrons as a function of transverse momentum (p_T) and collision centrality or the number of participant nucleons (N_part) for Au+Au collisions at sqrt(s_NN)=200 GeV. The v_{2,4} measurements at pseudorapidity |\eta|<=0.35 obtained with four separate reaction plane detectors positioned in the range 1.0<|\eta|<3.9 show good agreement, indicating the absence of significant \eta-dependent nonflow perturbations. Sizable values for v_4(p_T) are observed with a ratio v_4(p_T,N_part)/v_2^2(p_T,N_part)~0.8 for 50<N_part<200, which is compatible with the combined effects of a finite viscosity and initial eccentricity fluctuations. For N_part>200 this ratio increases up to 1.7 in the most central collisions.
Glauber quantities ($N_{part}$, $N_{coll}$, $b$) for Au+Au collisions at 200 GeV (PHENIX Run 2007)
Event-plane resolution factors vs. $N_{part}$ for $v_2$ and $v_4$ measurements for the indicated event planes.
Comparison of $v_2$ vs. $N_{part}$ and $v_4$ vs. $N_{part}$ for charged hadrons obtained with several reaction plane detectors for the $p_T$ selections indicated.
We present measurements of electrons and positrons from the semileptonic decays of heavy-flavor hadrons at midrapidity ($|y|<$ 0.35) in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ GeV. The data were collected in 2010 by the PHENIX experiment that included the new hadron-blind detector. The invariant yield of electrons from heavy-flavor decays is measured as a function of transverse momentum in the range $1<p_T^e<5$ GeV/$c$. The invariant yield per binary collision is slightly enhanced above the $p$$+$$p$ reference in Au$+$Au 0%--20%, 20%--40% and 40%--60% centralities at a comparable level. This may be a result of the interplay between initial-state Cronin effects, final-state flow, and energy loss for heavy-quark production at this low beam energy. The $v_2$ of electrons from heavy-flavor decays is nonzero when averaged between $1.3<p_T^e<2.5$ GeV/$c$ from $0<{\rm centrality}<40$% collisions at $\sqrt{s_{_{NN}}}=62.4$ GeV. For 20%--40% centrality collisions, the $v_2$ at $\sqrt{s_{_{NN}}}=62.4$ GeV is smaller than that for heavy flavor decays at $\sqrt{s_{_{NN}}}=200$ GeV. The $v_2$ of the electrons from heavy-flavor decay at the lower beam energy is also smaller than $v_2$ for pions. Both results indicate that the heavy-quarks interact with the medium formed in these collisions, but they may not be at the same level of thermalization with the medium as observed at $\sqrt{s_{_{NN}}}=200$ GeV.
Invariant yield of candidate electrons measured in Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV for different centrality bins. The yields are scaled by powers of 10 for clarity. The systematic uncertainty is shown as boxes and is, in many cases, comparable to the symbol size.
Cocktail prediction for photonic electron invariant yield. Invariant yield of (black dots) candidate electrons and (solid lines) electrons calculated from different photonic sources in Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV for MB events.
Invariant yield of heavy-flavor electrons measured in Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4 GeV for different centrality bins. The yields are scaled by powers of 10 for clarity. The uncertainty bars (boxes) show the statistical (systematic) uncertainties.
We present measurements of $e^+e^-$ production at midrapidity in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass ($m_{ee} <$ 5 GeV/$c^2$) and pair transverse momentum ($p_T$ $<$ 5 GeV/$c$), for minimum bias and for five centrality classes. The \ee 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 \pt range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to $2.3\pm0.4({\rm stat})\pm0.4({\rm syst})\pm0.2^{\rm model}$ or to $1.7\pm0.3({\rm stat})\pm0.3({\rm syst})\pm0.2^{\rm model}$ for minimum bias collisions when the open-heavy-flavor contribution is calculated with {\sc pythia} or {\sc 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.
Cocktail of hadronic sources for the 2010 run using the PYTHIA generator for the open heavy flavor contributions.
Invariant mass spectrum of $e^+e^-$ pairs in MB Au+Au collisions within the PHENIX acceptance compared to the cocktail of expected decays.
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.
The PHENIX experiment at RHIC has measured charged hadron yields at mid-rapidity over a wide range of transverse momentum (0.5 < p_T < 10 GeV/c) in Au+Au collisions at sqrt(s_NN)=200 GeV. The data are compared to pi^zero measurements from the same experiment. For both charged hadrons and neutral pions, the yields per nucleon-nucleon collision are significantly suppressed in central compared to peripheral and nucleon-nucleon collisions. The suppression sets in gradually and increases with increasing centrality of the collisions. Above 4-5 GeV/c in p_T, a constant and almost identical suppression of charged hadrons and pi^zeroes is observed. The p_T spectra are compared to published spectra from Au+Au at sqrt(s_NN)=130 in terms of x_t scaling. Central and peripheral pi^zero as well as peripheral charged spectra exhibit the same x_t scaling as observed in p+p data.
$p_T$ spectra of charged hadrons for minimum bias collisions along with spectra for 9 centrality classes derived from the pseudo-rapidity region $|\eta|$ < 0.18. Stat. stands for statistical error, syst. stands for the systematic errors and occ. stands for occupancy error.
$p_T$ spectra of charged hadrons for minimum bias collisions along with spectra for 9 centrality classes derived from the pseudo-rapidity region $|\eta|$ < 0.18. Stat. stands for statistical error, syst. stands for the systematic errors and occ. stands for occupancy error.
$p_T$ spectra of charged hadrons for minimum bias collisions along with spectra for 9 centrality classes derived from the pseudo-rapidity region $|\eta|$ < 0.18. Stat. stands for statistical error, syst. stands for the systematic errors and occ. stands for occupancy error.
We report the total and differential cross sections for $J/\psi$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/\psi$ photoproduction and its relation to the $J/\psi-$proton interaction. These measurements of $J/\psi$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon Generalized Parton Distribution (GPD) of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states.
$\gamma p \rightarrow J/\psi p$ total cross sections in bins of beam energy. The first uncertainties are statistical, and the second are systematic. There is an additional fully correlated systematic uncertainty of 19.5% on the total cross section, not included here.
$\gamma p \rightarrow J/\psi p$ differential cross sections 8.2–9.28 GeV beam energy range, average $t$ and beam energy in bins of $t$. The first cross section uncertainties are statistical, and the second are systematic. The overall average beam energy is 8.93 GeV. There is an additional fully correlated systematic uncertainty of 19.5% on the total cross section, not included here.
$\gamma p \rightarrow J/\psi p$ differential cross sections 9.28–10.36 GeV beam energy range, average $t$ and beam energy in bins of $t$. The first cross section uncertainties are statistical, and the second are systematic. The overall average beam energy is 9.86 GeV. There is an additional fully correlated systematic uncertainty of 19.5% on the total cross section, not included here.
The differential cross section for the production of direct photons in p+p collisions at sqrt(s)=200 GeV at midrapidity was measured in the PHENIX detector at the Relativistic Heavy Ion Collider. Inclusive-direct photons were measured in the transverse-momentum range from 5.5--25 GeV/c, extending the range beyond previous measurements. Event structure was studied with an isolation criterion. Next-to-leading-order perturbative-quantum-chromodynamics calculations give a good description of the spectrum. When the cross section is expressed versus x_T, the PHENIX data are seen to be in agreement with measurements from other experiments at different center-of-mass energies.
Cross section of midrapidity inclusive-direct photon production in $p+p$ collisions at $\sqrt{s}$ = 200 GeV as a function of transverse momentum ($p_T$). Asymmetric statistical uncertainties occur in $p_T$ bins with no tagged $π^0$ counts.
Ratio of isolated/inclusive-direct photon (Fig. 13). Upper(+) and lower bounds(-) on systematics can be different, and are listed separately.
Ratio of isolated/inclusive photon from $π^0$ (Fig. 13).
Neutral pion transverse momentum (pT) spectra at mid-rapidity (|y| < 0.35) were measured in Cu+Cu collisions at \sqrt s_NN = 22.4, 62.4, and 200 GeV. Relative to pi -zero yields in p+p collisions scaled by the number of inelastic nucleon-nucleon collisions (Ncoll) at the respective energies, the pi-zero yields for pT \ge 2 GeV/c in central Cu+Cu collisions at 62.4 and 200 GeV are suppressed, whereas an enhancement is observed at 22.4 GeV. A comparison with a jet quenching model suggests that final state parton energy loss dominates in central Cu+Cu collisions at 62.4 GeV and 200 GeV, while the enhancement at 22.4 GeV is consistent with nuclear modifications in the initial state alone.
Invariant $\pi^0$ yields in central Cu+Cu collisions and invariant $\pi^0$ cross sections in $p$+$p$ collisions at $\sqrt{s_{NN}}$ = 22.4 GeV. The error (tot.) includes the quadratic sum of the statistical and total systematic uncertainties.
Invariant $\pi^0$ yields in central Cu+Cu collisions and invariant $\pi^0$ cross sections in $p$+$p$ collisions at $\sqrt{s_{NN}}$ = 62.4 GeV. The error (tot.) includes the quadratic sum of the statistical and total systematic uncertainties.
Invariant $\pi^0$ yields in central Cu+Cu collisions and invariant $\pi^0$ cross sections in $p$+$p$ collisions at $\sqrt{s_{NN}}$ = 200 GeV. The error (tot.) includes the quadratic sum of the statistical and total systematic uncertainties.
The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV down to $p_T=0.4$ GeV/$c$. Photons are detected via photon conversions to $e^+e^-$ pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low $p_T$. We find an excess of direct photons above the $N_{\rm coll}$-scaled yield measured in $p$$+$$p$ collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/$c$ in the $p_T$ range from 0.6--2.0 GeV/$c$. While the shape of the $p_T$ distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with $N_{\rm part}^\alpha$, where $\alpha=1.48{\pm}0.08({\rm stat}){\pm}0.04({\rm syst})$.
Ratio $R_{\gamma}$ as function of photon $p_T$ from the 2007 and 2010 data sets in minimum-bias Au+Au collisions, and the $R_{\gamma}$ in the combined 2007+2010 measurement.
Ratio $R_{\gamma}$ as function of photon $p_T$ for the combined 2007 and 2010 data sets in different centrality bins.
Direct photon $p_T$ spectra in different centrality bins.
Unpolarized cross sections and double-helicity asymmetries of single-inclusive positive and negative charged hadrons at midrapidity from p+p collisions at sqrt(s)=62.4 GeV are presented. The PHENIX measurements for 1.0 < p_T < 4.5 GeV/c are consistent with perturbative QCD calculations at next-to-leading order in the strong coupling constant, alpha_s. Resummed pQCD calculations including terms with next-to-leading-log accuracy, yielding reduced theoretical uncertainties, also agree with the data. The double-helicity asymmetry, sensitive at leading order to the gluon polarization in a momentum-fraction range of 0.05 ~< x_gluon ~< 0.2, is consistent with recent global parameterizations disfavoring large gluon polarization.
Fit-function parameters for the efficiency curves for different hadron species.
Fit-function parameters for relative fractions of different species in the hadron mix.
Systematic uncertainties of cross-section measurements from various sources.
High-energy proton- and deuteron-nucleus collisions provide an excellent tool for studying a wide array of physics effects, including modifications of parton distribution functions in nuclei, gluon saturation, and color neutralization and hadronization in a nuclear environment, among others. All of these effects are expected to have a significant dependence on the size of the nuclear target and the impact parameter of the collision, also known as the collision centrality. In this article, we detail a method for determining centrality classes in p(d)+A collisions via cuts on the multiplicity at backward rapidity (i.e., the nucleus-going direction) and for determining systematic uncertainties in this procedure. For d+Au collisions at sqrt(s_NN) = 200 GeV we find that the connection to geometry is confirmed by measuring the fraction of events in which a neutron from the deuteron does not interact with the nucleus. As an application, we consider the nuclear modification factors R_{p(d)+A}, for which there is a potential bias in the measured centrality dependent yields due to auto-correlations between the process of interest and the backward rapidity multiplicity. We determine the bias correction factor within this framework. This method is further tested using the HIJING Monte Carlo generator. We find that for d+Au collisions at sqrt(s_NN)=200 GeV, these bias corrections are small and vary by less than 5% (10%) up to p_T = 10 (20) GeV. In contrast, for p+Pb collisions at sqrt(s_NN) = 5.02 TeV we find these bias factors are an order of magnitude larger and strongly p_T dependent, likely due to the larger effect of multi-parton interactions.
Different physical quantities characterizing $d$+Au collisions, and the bias-factor corrections, for nine PHENIX centrality bins.
Different physical quantities characterizing $d$+Au collisions, and the bias-factor corrections, for nine PHENIX centrality bins.
Different physical quantities characterizing $d$+Au collisions, and the bias-factor corrections, for four PHENIX centrality bins.
The PHENIX experiment at RHIC has measured transverse energy and charged particle multiplicity at mid-rapidity in Au+Au collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV as a function of centrality. The presented results are compared to measurements from other RHIC experiments, and experiments at lower energies. The sqrt(s_NN) dependence of dE_T/deta and dN_ch/deta per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of dE_T/deta and dN_ch/deta is similar at all measured incident energies. At RHIC energies the ratio of transverse energy per charged particle was found independent of centrality and growing slowly with sqrt(s_NN). A survey of comparisons between the data and available theoretical models is also presented.
$B$/$A$ ratio from the fit to the data.
$B$/$A$ ratio from the fit to the data.
Parameter $\alpha$ from the fit to the data.
We present the first results of meson production in the K^+K^- decay channel from Au+Au collisions at sqrt(s_NN) = 200 GeV as measured at mid-rapidity by the PHENIX detector at RHIC. Precision resonance centroid and width values are extracted as a function of collision centrality. No significant variation from the PDG accepted values is observed. The transverse mass spectra are fitted with a linear exponential function for which the derived inverse slope parameter is seen to be constant as a function of centrality. These data are also fitted by a hydrodynamic model with the result that the freeze-out temperature and the expansion velocity values are consistent with the values previously derived from fitting single hadron inclusive data. As a function of transverse momentum the collisions scaled peripheral.to.central yield ratio RCP for the is comparable to that of pions rather than that of protons. This result lends support to theoretical models which distinguish between baryons and mesons instead of particle mass for explaining the anomalous proton yield.
Average number of participants and collisions in Au + Au reaction at RHIC for different centralities determined from a Glauber model.
$\phi$ meson mass centroid and width for minimum-bias Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Minimum-bias $dN/dy$ and $T$ for different subsystem combinations.
Measurements of the fractional momentum loss ($S_{\rm loss}\equiv{\delta}p_T/p_T$) of high-transverse-momentum-identified hadrons in heavy ion collisions are presented. Using $\pi^0$ in Au$+$Au and Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=62.4$ and 200 GeV measured by the PHENIX experiment at the Relativistic Heavy Ion Collider and and charged hadrons in Pb$+$Pb collisions measured by the ALICE experiment at the Large Hadron Collider, we studied the scaling properties of $S_{\rm loss}$ as a function of a number of variables: the number of participants, $N_{\rm part}$, the number of quark participants, $N_{\rm qp}$, the charged-particle density, $dN_{\rm ch}/d\eta$, and the Bjorken energy density times the equilibration time, $\varepsilon_{\rm Bj}\tau_{0}$. We find that the $p_T$ where $S_{\rm loss}$ has its maximum, varies both with centrality and collision energy. Above the maximum, $S_{\rm loss}$ tends to follow a power-law function with all four scaling variables. The data at $\sqrt{s_{_{NN}}}$=200 GeV and 2.76 TeV, for sufficiently high particle densities, have a common scaling of $S_{\rm loss}$ with $dN_{\rm ch}/d\eta$ and $\varepsilon_{\rm Bj}\tau_{0}$, lending insight on the physics of parton energy loss.
Global variables for Au+Au collisions at RHIC from PHENIX.
Global variables for Au+Au collisions at RHIC from PHENIX.
Global variables for Cu+Cu collisions at RHIC from PHENIX.
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured $\phi$ meson production and its nuclear modification in asymmetric Cu$+$Au heavy-ion collisions at $\sqrt{s_{NN}}=200$ GeV at both forward Cu-going direction ($1.2<y<2.2$) and backward Au-going direction ($-2.2<y<-1.2$), rapidities. The measurements are performed via the dimuon decay channel and reported as a function of the number of participating nucleons, rapidity, and transverse momentum. In the most central events, 0\%--20\% centrality, the $\phi$ meson yield integrated over $1<p_T<5$ GeV/$c$ prefers a smaller value, which means a larger nuclear modification, in the Cu-going direction compared to the Au-going direction. Additionally, the nuclear-modification factor in Cu$+$Au collisions averaged over all centrality is measured to be similar to the previous PHENIX result in $d$$+$Au collisions for these rapidities.
Invariant yield as a function of the number of participating nucleons for 1.2 < $|y|$ < 2.2 and 1 < $p_T$ < 5 GeV/$c$. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
Invariant yield as a function of transverse momentum for 1.2 < $|y|$ < 2.2 and 0%–93% centrality. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
Invariant yield as a function of rapidity for 1 < $p_T$ < 5 GeV/$c$ and 0%–93% centrality. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
We report the transverse single-spin asymmetries of $J/\psi$ production at forward and backward rapidity, $1.2<|y|<2.2$, as a function of $J/\psi$ transverse momentum ($p_T$) and Feynman-$x$ ($x_F$). The data analyzed were recorded by the PHENIX experiment at the Relativistic Heavy Ion Collider in 2015 from $p$$+$$p$, $p$$+$Al, and $p$$+$Au collisions with transversely polarized proton beams at $\sqrt{s_{_{NN}}}=200$ GeV. At this collision energy, single-spin asymmetries for heavy-flavor particle production of $p$$+$$p$ collisions provide access to the spin-dependent gluon distribution and higher-twist correlation functions inside the nucleon, such as the gluon Qiu-Sterman and trigluon correlation functions. Proton+nucleus collisions offer an excellent opportunity to study nuclear effects on the correlation functions. The data indicate negative asymmetries at the two-standard-deviation level in the $p$$+$Au data for $p_T<2$ GeV/$c$ at both forward and backward rapidity, while in $p$$+$$p$ and $p$$+$Al collisions the asymmetries are consistent with zero within the range of experimental uncertainties.
Forward [$x_F$ > 0] $A^{J/\psi}_N$ vs low $p_T$ for $p$+$p$, $p$+Al, and $p$+Au collisions.
Forward [$x_F$ > 0] $A^{J/\psi}_N$ vs high $p_T$ for $p$+$p$, $p$+Al, and $p$+Au collisions.
Backward [$x_F$ < 0] $A^{J/\psi}_N$ vs low $p_T$ for $p$+$p$, $p$+Al, and $p$+Au collisions.
We present azimuthal angle correlations of intermediate transverse momentum (1-4 GeV/c) hadrons from {dijets} in Cu+Cu and Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV. The away-side dijet induced azimuthal correlation is broadened, non-Gaussian, and peaked away from \Delta\phi=\pi in central and semi-central collisions in all the systems. The broadening and peak location are found to depend upon the number of participants in the collision, but not on the collision energy or beam nuclei. These results are consistent with sound or shock wave models, but pose challenges to Cherenkov gluon radiation models.
The measured correlation $C(\Delta\phi)$ and the dijet correlation $J(\Delta\phi)$ in central Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Dijet correlations in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV.
Dijet correlations in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV.
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.
Measurements of bottomonium production in heavy ion and $p$$+$$p$ collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three $\Upsilon$ states, $\Upsilon(1S+2S+3S)$, was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au$+$Au and $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The $\Upsilon(1S+2S+3S)\rightarrow e^+e^-$ differential cross section at midrapidity was found to be $B_{\rm ee} d\sigma/dy =$ 108 $\pm$ 38 (stat) $\pm$ 15(syst) $\pm$ 11 (luminosity) pb in $p$$+$$p$ collisions. The nuclear modification factor in the 30\% most central Au$+$Au collisions indicates a suppression of the total $\Upsilon$ state yield relative to the extrapolation from $p$$+$$p$ collision data. The suppression is consistent with measurements made by STAR at RHIC and at higher energies by the CMS experiment at the Large Hadron Collider.
Summary of the measured $\Upsilon$ invariant multiplicities, $BdN/dy$, for one $p + p$ three Au + Au data sets.
Summary of the measured $\Upsilon$ nuclear modification factors, $R_{AA}$, for Au + Au data sets.
Summary of the measured $\Upsilon$ nuclear modification factors, $R_{AA}$, for Au + Au data sets.
Two particle azimuthal correlation functions are presented for charged hadrons produced in Au + Au collisions at RHIC sqrt(s_NN) = 130 GeV. The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values v_2 show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone, epsilon, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low p_T. A breakdown of this epsilon scaling is observed for charged hadrons with p_T > 1.0 GeV/c for the most central collisions.
Azimuthal correlation functions for charged hadrons as a function of centrality and $p_T$ selection. The solid curves represent Fourier fits following Eq. (2). Error bars are statistical only.
$v_2$ vs. centrality for several $p_T$ selections. [F] and [A] indicate results obtained with the fixed-$p_T$ and assorted-$p_T$ methods respectively. Systematic errors are estimated to be $\sim 5$%; they are dominated by the normalization of the correction function for real tracks. For the centrality range 0-5%, the data points are statistically uncertain and the points are omitted.
$v_2$ vs. centrality for several $p_T$ selections. [F] and [A] indicate results obtained with the fixed-$p_T$ and assorted-$p_T$ methods respectively. Systematic errors are estimated to be $\sim 5$%; they are dominated by the normalization of the correction function for real tracks. For the centrality range 0-5%, the data points are statistically uncertain and the points are omitted.
The azimuthal distribution of identified pi^0 and inclusive photons has been measured in sqrt{s_{NN}} = 200 GeV Au+Au collisions with the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). The second harmonic parameter (v_2) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon v_2 is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured p_T range 1-6 GeV/c. An attempt is made to extract v_2 of direct photons.
The measured $v_2$ of $\pi^0$ ($v_2^{\pi^0}$) for 4 centrality selections.
The measured $v_2$ of inclusive photon ($v_2^{inclusive \gamma}$) for 4 centrality selections.
The expected photon $v_2$ from hadronic decay $v_2^{(b.g.)}$ and the subtracted $v_2$ quantity $R v_2^{(inclusive \gamma)}$ - $v_2^{(b.g.)}$.
We report a measurement of $e^+e^-$ pairs from semileptonic heavy-flavor decays in $p$+$p$ collisions at $\sqrt{s_{NN}}=200$~GeV. The $e^+e^-$ pair yield from $b\bar{b}$ and $c\bar{c}$ is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and $p_T$. We used three different event generators, {\sc pythia}, {\sc mc@nlo}, and {\sc powheg}, to simulate the $e^+e^-$ spectra from $c\bar{c}$ and $b\bar{b}$ 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\bar{b}$ than for $c\bar{c}$. 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.
Step by step extrapolation from the number of $e^+e^-$ pairs for $m_{e^+e^-}$ > 1.16 GeV/$c^2$ from $c\bar{c}$ in the PHENIX acceptance to the number of $c\bar{c}$ pairs in 4$\pi$ for PYTHIA, MC@NLO, and POWHEG. Numbers are in units of pairs per event using the $c\bar{c}$ cross sections determined in this paper.
Step by step extrapolation from the number of $e^+e^-$ pairs for $m_{e^+e^-}$ > 1.16 GeV/$c^2$ from $b\bar{b}$ in the PHENIX acceptance to the number of $b\bar{b}$ pairs in 4$\pi$ for PYTHIA, MC@NLO, and POWHEG. Numbers are in units of pairs per event using the $b\bar{b}$ cross sections determined in this paper.
Summary of $c\bar{c}$ and $b\bar{b}$ cross sections measured in $p$+$p$ collisions using three different generators, PYTHIA, MC@NLO, and POWHEG.
The production of prompt $\Lambda^+_\mathrm{c}$ baryons is measured via the exclusive decay channel $\Lambda^+_\mathrm{c}$$\to$ pK$^-\pi^+$ at a center-of-mass energy per nucleon pair of 5.02 TeV, using proton-proton (pp) and lead-lead (PbPb) collision data collected by the CMS experiment at the CERN LHC. The pp and PbPb data were obtained in 2017 and 2018 with integrated luminosities of 252 and 0.607 nb$^{-1}$, respectively. The measurements are performed within the $\Lambda^+_\mathrm{c}$ rapidity interval $\vert y \vert$$\lt$ 1 with transverse momentum ($p_\mathrm{T}$) ranges of 3-30 and 6-40 GeV/$c$ for pp and PbPb collisions, respectively. Compared to the yields in pp collisions scaled by the expected number of nucleon-nucleon interactions, the observed yields of $\Lambda^+_\mathrm{c}$ with $p_\mathrm{T}$$\gt$ 10 GeV/$c$ are strongly suppressed in PbPb collisions. The level of suppression depends significantly on the collision centrality. The $\Lambda^+_\mathrm{c}$ / D$^0$ production ratio is similar in PbPb and pp collisions at $p_\mathrm{T}$$\gt$ 10 GeV/$c$, suggesting that the coalescence process does not play a dominant role in prompt $\Lambda^+_\mathrm{c}$ baryon production at higher $p_\mathrm{T}$.
The product of acceptance and efficiency ($A \epsilon$) as a function of $p_{\mathrm{T}}$ for prompt $\Lambda^+_c$ in pp collisions and within centrality regions of 0-90, 0-10, 10-30, 30-50 and 50-90% in PbPb collisions.
The $p_{\mathrm{T}}$ differential cross sections for prompt $\Lambda^+_c$ production in pp collisions. The global fit uncertainty is 8.6%.
The $\mathrm{T_{AA}}$-scaled $\Lambda^+_c$ yields as a function of $p_{\mathrm{T}}$ for PbPb collisions within centrality regions of 0-90, 0-10, 10-30, 30-50 and 50-90%.
We report PHENIX measurements of the correlation of a trigger hadron at intermediate transverse momentum (2.5<p_{T,trig}<4 GeV/c), with associated mesons or baryons at lower p_{T,assoc}, in Au+Au collisions at sqrt(s_NN) = 200 GeV. The jet correlations for both baryons and mesons show similar shape alterations as a function of centrality, characteristic of strong modification of the away-side jet. The ratio of jet-associated baryons to mesons for this jet increases with centrality and p_{T,assoc} and, in the most central collisions, reaches a value similar to that for inclusive measurements. This trend is incompatible with in-vacuum fragmentation, but could be due to jet-like contributions from correlated soft partons which recombine upon hadronization.
<p>Correlation functions for associated partner mesons for centrality selections of 20-40% and 70-90%.</p> <p><i>Note that only statistical uncertainties are available.</i></p>
<p>Correlation functions for associated partner baryons for centrality selections of 20-40% and 70-90%.</p> <p><i>Note that only statistical uncertainties are available.</i></p>
<p>Jet-pair distributions for associated mesons for $1 < p_{T,assoc} < 1.3\ \mathrm{GeV}/c$ and $1.6 < p_{T,assoc} < 2.0\ \mathrm{GeV}/c$. Results are for a hadron trigger $2.5 < p_T < 4.0\ \mathrm{GeV}/c$ and centrality selections of 0-20% and 20-40%.</p> <p><i>Note that only statistical uncertainties are available.</i></p>
The PHENIX experiment has measured $\phi$ meson production in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV using the dimuon and dielectron decay channels. The $\phi$ meson is measured in the forward (backward) $d$-going (Au-going) direction, $1.2<y<2.2$ ($-2.2<y<-1.2$) in the transverse-momentum ($p_T$) range from 1--7 GeV/$c$, and at midrapidity $|y|<0.35$ 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.
Invariant yields of $\phi$ meson production as a function of $p_T$ at different $d$+Au centrality classes. Type B represents uncertainties that are correlated from point to point.
Invariant yields of $\phi$ meson production as a function of $p_T$ at different $d$+Au centrality classes. Type B represents uncertainties that are correlated from point to point.
Invariant yields of $\phi$ meson production as a function of $p_T$ at different $d$+Au centrality classes. Type B represents uncertainties that are correlated from point to point.
The PHENIX experiment has measured open heavy-flavor production via semileptonic decay muons over the transverse momentum range 1 < pT < 6 GeV/c at forward and backward rapidity (1.4 < |y| < 2.0) in d+Au and p+p collisions at ?sNN = 200 GeV. In central d+Au collisions an enhancement (suppression) of heavy-flavor muon production is observed at backward (forward) rapidity relative to the yield in p+p collisions scaled by the number of binary collisions. Modification of the gluon density distribution in the Au nucleus contributes in terms of anti-shadowing enhancement and shadowing suppression; however, the enhancement seen at backward rapidity exceeds expectations from this effect alone. These results, implying an important role for additional cold nuclear matter effects, serves as a key baseline for heavy-quark measurements in A+A collisions and in constraining the magnitude of charmonia breakup effects at the Relativistic Heavy Ion Collider and the Large Hadron Collider.
Invariant yield of negatively charged heavy-flavor muons as a function of $p_T$ in $d$+Au collisions for different centralities at (a) backward rapidity (Au-going) and (b) forward rapidity (d-going).
Invariant yield of negatively charged heavy-flavor muons as a function of $p_T$ in $d$+Au collisions for different centralities at (a) backward rapidity (Au-going) and (b) forward rapidity (d-going).
Invariant yield of negatively charged heavy-flavor muons as a function of $p_T$ in $d$+Au collisions for different centralities at (a) backward rapidity (Au-going) and (b) forward rapidity (d-going).
Transverse momentum (p^e_T) spectra of electrons from semileptonic weak decays of heavy flavor mesons in the range of 0.3 < p^e_T < 9.0 GeV/c have been measured at mid-rapidity (|eta| < 0.35) by the PHENIX experiment at the Relativistic Heavy Ion Collider in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The nuclear modification factor R_AA with respect to p+p collisions indicates substantial energy loss of heavy quarks in the produced medium. In addition, the azimuthal anisotropy parameter v_2 has been measured for 0.3 < p^e_T < 5.0 GeV/c in Au+Au collisions. Comparisons of R_AA and v_2 are made to various model calculations.
Charm cross section per $N$+$N$ collision in centrality bins in Au+Au and $p$+$p$. $T_{AA}$ is the nuclear overlap integral of the centrality.
Charm cross section per $N$+$N$ collision in centrality bins in Au+Au and $p$+$p$. $T_{AA}$ is the nuclear overlap integral of the centrality.
Heavy-flavor $e^{\pm}$ $v_2$ from Au+Au collisions, for the centralities indicated.
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 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 $\Delta\phi$.
We present measured J/psi production rates in d+Au collisions at sqrt(s_NN) = 200 GeV over a broad range of transverse momentum (p_T=0-14 GeV/c) and rapidity (-2.2<y<2.2). We construct the nuclear-modification factor R_dAu for these kinematics and as a function of collision centrality (related to impact parameter for the R_dAu collision). We find that the modification is largest for collisions with small impact parameters, and observe a suppression (R_dAu<1) for p_T<4 GeV/c at positive rapidities. At negative rapidity we observe a suppression for p_T<2 GeV/c then an enhancement (R_dAu>1) for p_T>2 GeV/c. The observed enhancement at negative rapidity has implications for the observed modification in heavy-ion collisions at high p_T.
$J/\psi$ invariant yield as a function of $p_T$ for $p+p$ and 0–100% centrality integrated $d$+Au collisions. The type C systematic uncertainty for each distribution is given as a percentage in the legend. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
$J/\psi$ invariant yield as a function of $p_T$ for $p+p$ and 0–100% centrality integrated $d$+Au collisions. The type C systematic uncertainty for each distribution is given as a percentage in the legend. Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
$J/\psi$ invariant yield as a function of $p_T$ for $p+p$ and 0–100% centrality integrated $d$+Au collisions. The type C systematic uncertainty for each distribution is given as a percentage in the legend.Type A represents uncertainties that are uncorrelated from point to point, Type B represents uncertainties that are correlated from point to point, and Type C represents uncertainties in the overall normalization.
Two particle correlations between identified meson and baryon trigger particles with 2.5 < p_T < 4.0 GeV/c and lower p_T charged hadrons have been measured at midrapidity by the PHENIX experiment at RHIC in p+p, d+Au and Au+Au collisions at sqrt(s_NN) = 200 GeV. The probability of finding a hadron near in azimuthal angle to the trigger particle is almost identical for leading mesons and baryons for non-central Au+Au. The yield for both trigger baryons and mesons is significantly higher in Au+Au than in p+p and d+Au, except for trigger baryons in central collisions. The baryon excess is likely to arise predominantly from hard scattering processes.
$\Delta\phi$ distributions for meson and baryon triggers with 2.5 < $p_T$ < 4.0 GeV/$c$ and associated charged hadrons with 1.7 < $p_T$ < 2.5 GeV/$c$ for five centralities in Au+Au collisions.
$\Delta\phi$ distributions for meson triggers with 2.5 < $p_T$ < 4.0 GeV/$c$ and associated charged hadrons with 1.7 < $p_T$ < 2.5 GeV/$c$ in $d$+Au collisions.
$\Delta\phi$ distributions unidentified triggers with 2.5 < $p_T$ < 4.0 GeV/$c$ and associated charged hadrons with 1.7 < $p_T$ < 2.5 GeV/$c$ in $p$+$p$ collisions.
We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at mid-rapidity in deuteron-gold (d+Au) and proton-proton (p+p) collisions at sqrt(s_NN) = 200 GeV. Jet structures are observed in the correlations which we quantify in terms of the conditional yield and angular width of away side partners. The kinematic region studied here samples partons in the gold nucleus carrying nucleon momentum fraction x~0.1 to x~0.01. Within this range, we find no x dependence of the jet structure in d+Au collisions.
Azimuthal angle correlation functions. Note that the y-axis is zero-suppressed on the middle and bottom panels. In the additonal resource, the Gaussian widths from the fits and the signal to background ration integrated over $\pi$ - 1 < $\Delta\phi$ < $\pi$ + 1 are shown.
Conditional yields (CY) shown as a function of trigger particle pseudorapitidy for trigger particle $p_T$ from 2.5 to 4.0 and associated particle $p_T$ from 1.0 to 2.5 GeV/$c$. The additional $\pm$0.037 systematic error on the mid-rapidity $p+p$ point is from jet yield extraction. There is a 1% point-by-point systematical error on all points except central arm triggers. There is also a 10% systematic error for all data points due to the determination of associated particle efficiency. For $p + p$ point, forward and backward trigger are combined, so the results are identical.
$I_{dAu}$ vs. $p_T^{assoc}$ for different centrality, $p_T^{trig}$ and $\eta^{trig}$ bins.
Measurements of the anisotropy parameter v_2 of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum p_T, and transverse kinetic energy KE_T at midrapidity (|\eta|<0.35) in Au+Au collisions at sqrt(s_NN) = 200 GeV are presented. Pions and protons are identified up to p_T = 6 GeV/c, and kaons up to p_T = 4 GeV/c, by combining information from time-of-flight and aerogel Cherenkov detectors in the PHENIX Experiment. The scaling of v_2 with the number of valence quarks (n_q) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KE_T/n_q in noncentral Au+Au collisions (20--60%), but this scaling remains valid in central collisions (0--10%).
Identified hadron $v_2$ in central (0–20% centrality, left panels) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Panels (a) and (b) show $v_2$ as a function of transverse momentum $p_T$. The $v_2$ of all species for centrality 0–20% has been scaled up by a factor of 1.6 for better comparison with results of 20–60% centrality. The error bars (shaded boxes) represent the statistical (systematic) uncertainties. The systematic uncertainties shown are type A and B only.
Identified hadron $v_2$ in central (0–20% centrality, left panels) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Panels (a) and (b) show $v_2$ as a function of transverse momentum $p_T$. The $v_2$ of all species for centrality 0–20% has been scaled up by a factor of 1.6 for better comparison with results of 20–60% centrality. The error bars (shaded boxes) represent the statistical (systematic) uncertainties. The systematic uncertainties shown are type A and B only.
Identified hadron $v_2$ in central (0–20% centrality, left panels) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Panels (a) and (b) show $v_2$ as a function of transverse momentum $p_T$. The $v_2$ of all species for centrality 0–20% has been scaled up by a factor of 1.6 for better comparison with results of 20–60% centrality. The error bars (shaded boxes) represent the statistical (systematic) uncertainties. The systematic uncertainties shown are type A and B only.
We have measured the azimuthal anisotropy of pi0's for 1 < pT < 18 GeV/c for Au+Au collisions at sqrt s_NN = 200 GeV. The observed anisotropy shows a gradual decrease in 3 < pT < 7 - 10 GeV/c, but remains positive beyond 10 GeV/c. The magnitude of this anisotropy is under-predicted, up to at least 10 GeV/c, by current perturbative QCD (pQCD) energy-loss model calculations. An estimate of the increase in anisotropy expected from initial-geometry modification due to gluon saturation effects and initial-geometry fluctuations is insufficient to account for this discrepancy. Calculations which implement a path length dependence steeper than what is implied by current pQCD energy-loss models, show reasonable agreement with the data.
$\pi^0$ $v_2$ using the reaction plane determined with MPC and RXN$_{in}$ combined as a function of $p_T$ for different centralities.
Ratios of $v_2$ measured separately using MPC and RXN$_{in}$ to combine results.
$v_2$ vs $N_{part}$ in two $p_T$ ranges and $R_{AA}$ vs $N_{part}$ in the same $p_T$ ranges.
PHENIX has measured the centrality dependence of mid-rapidity pion, kaon and proton transverse momentum distributions in d+Au and p+p collisions at sqrt(s_NN) = 200 GeV. The p+p data provide a reference for nuclear effects in d+Au and previously measured Au+Au collisions. Hadron production is enhanced in d+Au, relative to independent nucleon-nucleon scattering, as was observed in lower energy collisions. The nuclear modification factor for (anti) protons is larger than that for pions. The difference increases with centrality, but is not sufficient to account for the abundance of baryon production observed in central Au+Au collisions at RHIC. The centrality dependence in d+Au shows that the nuclear modification factor increases gradually with the number of collisions suffered by each participant nucleon. We also present comparisons with lower energy data as well as with parton recombination and other theoretical models of nuclear effects on particle production.
Mean number of binary collisions, particpating nucleons from the Au nucleus, number of collisions per participating deuteron nucleon, and trigger bias corrections for the $d$+Au centrality bins.
Transverse momentum in GeV/$c$ for $\pi^{\pm}$.
Transverse momentum in GeV/$c$ for $\pi^{\pm}$.
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 three 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.
Forward neutron $A_N$ in $p$+$A$ collisions for $A$ = 1 ($p$), 27 (Al), and 197 (Au), for ZDC inclusive, ZDC $\otimes$ BBC-tag, and ZDC $\otimes$ BBC-veto triggered samples. The 3% scale uncertainty is from the polarization normalization uncertaintiy.
We present measurements of the transverse-momentum dependence of elliptic flow $v_2$ for identified pions and (anti)protons at midrapidity ($|\eta|<0.35$), in 0%--5% central $p$$+$Au and $^3$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. When taken together with previously published measurements in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, the results cover a broad range of small-collision-system multiplicities and intrinsic initial geometries. We observe a clear mass-dependent splitting of $v_2(p_{T})$ in $d$$+$Au and $^3$He$+$Au collisions, just as in large nucleus-nucleus ($A$$+$$A$) collisions, and a smaller splitting in $p$$+$Au collisions. Both hydrodynamic and transport model calculations successfully describe the data at low $p_T$ ($< 1.5$ GeV/$c$), but fail to describe various features at higher $p_T$. In all systems, the $v_2$ values follow an approximate quark-number scaling as a function of the hadron transverse kinetic energy per constituent quark($KE_T/n_q$), which was also seen previously in $A$$+$$A$ collisions.
Values of $v_2$($p_T$) for kaons in central 0-5% $p$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Values of $v_2$($p_T$) for kaons in central 0-5% $^3$He+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Transverse momentum dependence of $v_2$ for identified pions and protons within $|\eta|$ < 0.35 in 0-5% central $p$+Au collisions.
Charged-pion-interferometry measurements were made with respect to the 2$^{\rm nd}$- and 3$^{\rm rd}$-order event plane for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. A strong azimuthal-angle dependence of the extracted Gaussian-source radii was observed with respect to both the 2$^{\rm nd}$- and 3$^{\rm rd}$-order event planes. The results for the 2$^{\rm nd}$-order dependence indicate that the initial eccentricity is reduced during the medium evolution, but not reversed in the final state, which is consistent with previous results. In contrast, the results for the 3$^{\rm rd}$-order dependence indicate that the initial triangular shape is significantly reduced and potentially reversed by the end of the medium evolution, and that the 3$^{\rm rd}$-order oscillations are largely dominated by the dynamical effects from triangular flow.
The azimuthal dependence of $R^2_s$, $R^2_o$, $R^2_l$, and $R^2_{os}$ for charged pions in 0.2 < $k_T$ < 2.0 GeV/$c$ with respect to second-(a)-(d) and third-order (e)-(h) event plane in Au + Au collisions at $\sqrt{S_{NN}}$ 200 GeV.
The azimuthal dependence of $R^2_s$, $R^2_o$, $R^2_l$, and $R^2_{os}$ for charged pions in 0.2 < $k_T$ < 2.0 GeV/$c$ with respect to second-(a)-(d) and third-order (e)-(h) event plane in Au + Au collisions at $\sqrt{S_{NN}}$ 200 GeV.
The solid points are the oscillation amplitudes relative to the average of HBT radii for four different combinations (a) $2R^{2}_{s,n}/R^{2}_{s,0}$, (b) $2R^{2}_{os,n}/R^{2}_{s,0}$, (c) $2R^{2}_{o,n}/R^{2}_{o,0}$, and (d) $2R^{2}_{o,n}/R^{2}_{s,0}$ as a function of initial spatial anisotropy ($\varepsilon_{n}$), which are calculated using the Glauber model.
The dependence of transverse momentum spectra of neutral pions and eta mesons with p_T <16 GeV/c and p_T < 12 GeV/c, respectively, on the centrality of the collision has been measured at mid-rapidity by the PHENIX experiment at RHIC in d+Au collisions at sqrt(s_(NN)) = 200 GeV. The measured yields are compared to those in p + p collisions at the same sqrt(s_(NN)) scaled by the number of underlying nucleon-nucleon collisions in d+Au. At all centralities the yield ratios show no suppression, in contrast to the strong suppression seen for central Au+Au collisions at RHIC. Only a weak p_T and centrality dependence can be observed.
Invariant yields at mid-rapidity for $\pi^0$ and $\eta$ in $d$+Au collisions as a function of $p_T$ for different centrality selections.
Invariant yields at mid-rapidity for $\pi^0$ and $\eta$ in $d$+Au collisions as a function of $p_T$ for different centrality selections.
Invariant yields at mid-rapidity for $\pi^0$ and $\eta$ in $d$+Au collisions as a function of $p_T$ for different centrality selections.
Measurements of neutral pion production at midrapidity in sqrt(s_NN) = 200 GeV Au+Au collisions as a function of transverse momentum, p_T, collision centrality, and angle with respect to reaction plane are presented. The data represent the final pi^0 results from the PHENIX experiment for the first RHIC Au+Au run at design center-of-mass-energy. They include additional data obtained using the PHENIX Level-2 trigger with more than a factor of three increase in statistics over previously published results for p_T > 6 GeV/c. We evaluate the suppression in the yield of high-p_T pi^0's relative to point-like scaling expectations using the nuclear modification factor R_AA. We present the p_T dependence of R_AA for nine bins in collision centrality. We separately integrate R_AA over larger p_T bins to show more precisely the centrality dependence of the high-p_T suppression. We then evaluate the dependence of the high-p_T suppression on the emission angle \Delta\phi of the pions with respect to event reaction plane for 7 bins in collision centrality. We show that the yields of high-p_T pi^0's vary strongly with \Delta\phi, consistent with prior measurements. We show that this variation persists in the most peripheral bin accessible in this analysis. For the peripheral bins we observe no suppression for neutral pions produced aligned with the reaction plane while the yield of pi^0's produced perpendicular to the reaction plane is suppressed by more than a factor of 2. We analyze the combined centrality and \Delta\phi dependence of the pi^0 suppression in different p_T bins using different possible descriptions of parton energy loss dependence on jet path-length averages to determine whether a single geometric picture can explain the observed suppression pattern.
Neutral pion invariant yields as a function of $p_T$ measured in minimum bias and 9 centrality classes in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Neutral pion invariant yields as a function of $p_T$ measured in minimum bias and 9 centrality classes in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Neutral pion invariant yields as a function of $p_T$ measured in minimum bias and 9 centrality classes in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
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