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.
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).
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 $\pi^{\pm}$.
The first measurement of direct photons in Au+Au collisions at sqrt(s_NN) = 200 GeV is presented. The direct photon signal is extracted as a function of the Au+Au collision centrality and compared to NLO pQCD calculations. The direct photon yield is shown to scale with the number of nucleon-nucleon collisions for all centralities.
Double ratio of measured $(\gamma/\pi^0)_{Measured}$ invariant yield ratio to the background decay $(\gamma/\pi^0)_{Background}$ ratio as a function of $p_T$ for minimum bias and for five centralities of Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The bin range is not an uncertainty in the x-axis because the actual uncertainty by having the finite bin width is corrected for by the bin-shift correction. These bins were constructed using the corrected finite values as centers.
Double ratio of measured $(\gamma/\pi^0)_{Measured}$ invariant yield ratio to the background decay $(\gamma/\pi^0)_{Background}$ ratio as a function of $p_T$ for minimum bias and for five centralities of Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The bin range is not an uncertainty in the x-axis because the actual uncertainty by having the finite bin width is corrected for by the bin-shift correction. These bins were constructed using the corrected finite values as centers.
Direct $\gamma$ invariant yields as a function of transverse momentum for 9 centrality selections and minimum bias Au+AU collisions at $\sqrt{s_{NN}}$ = 200 GeV. Data with no errors represents 90% confidence level upper limit. The bin range is not an uncertainty in the x-axis because the actual uncertainty by having the finite bin width is corrected for by the bin-shift correction. These bins were constructed using the corrected finite values as centers.
The PHENIX collaboration presents a systematic study of $\pi^0$ production from $p$ $+$ $p$, $p$ $+$Al, $p$ $+$Au, $d$ $+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Measurements were performed with different centrality selections as well as the total inelastic, 0%--100%, selection for all collision systems. For 0%--100% collisions, the nuclear modification factors, $R_{xA}$, are consistent with unity for $p_T$ above 8 GeV/$c$, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are similar for all systems for the same centrality class. It is shown that for high-$p_T$-$\pi^0$ production, the nucleons in the $d$ and $^3$He interact mostly independently with the Au nucleus and that the counter intuitive centrality dependence is likely due to a physical correlation between multiplicity and the presence of a hard scattering process. These observations disfavor models where parton energy loss has a significant contribution to nuclear modifications in small systems. Nuclear modifications at lower $p_T$ resemble the Cronin effect -- an increase followed by a peak in central or inelastic collisions and a plateau in peripheral collisions. The peak height has a characteristic ordering by system size as $p$ $+$Au $>$ $d$ $+$Au $>$ $^{3}$He$+$Au $>$ $p$ $+$Al. For collisions with Au ions, current calculations based on initial state cold nuclear matter effects result in the opposite order, suggesting the presence of other contributions to nuclear modifications, in particular at lower $p_T$.
Differential cross section of $\pi^0$ in p+p collisions at $\sqrt{s}$ = 200 GeV
Nuclear modification factors from inelastic (a) p+Al, (b) p+Au, (c) d+Au, and (d) $^{3}$HeAu collisions at $\sqrt{s}$ = 200 GeV. The right boxes are the $N_{coll}$ uncertainties from the Glauber model, while the left box represents the overall normalization uncertainty from p+p collisions
Nuclear modification factors in p+Al, p+Au, d+Au, and $^{3}$He+Au in five centrality bins and for inelastic collisions at $\sqrt{s}$ = 200 GeV. The right boxes are the uncertainties of the $N_{coll}$ collisions from the Glauber model, while the left box represents the overall normalization uncertainty from p+p collisions
PHENIX has measured the centrality dependence of charged hadron p_T spectra from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction of the contribution from hard scattering to high p_T hadron production. For central collisions the yield at high p_T is shown to be suppressed compared to binary nucleon-nucleon collision scaling of p+p data. This suppression is monotonically increasing with centrality, but most of the change occurs below 30% centrality, i.e. for collisions with less than about 140 participating nucleons. The observed p_T and centrality dependence is consistent with the particle production predicted by models including hard scattering and subsequent energy loss of the scattered partons in the dense matter created in the collisions.
Number of participants and binary collisions and their systematic errors for the individual centrality selections used in this analysis. Also given is the ratio of the number of binary collisions for the most central sample relative to the one for each sample. The last column quantifies the ratio of binary collisions to participant pairs.
The ratio $p/h$ represents the proton plus anti-proton yield relative to the total charged hadron multiplicity. This shows the $p_T$ dependence of $p/h$ for minimum bias events.
The top panel gives the nuclear modification factor $R_{AA}$ for three exclusive $p_T$ regions as a function of the centrality of the collision. The lower panel shows essentially the same quantity but normalized to the number of participant pairs rather than to the number of binary collisions. The dotted line indicates the expectation for scaling with the number of binary collisions (top) or with the number of participants (bottom). Only statistical errors are shown. The systematic error on the scale and the centrality dependence are identical to the errors shown in Fig. 5. These errors are correlated, i.e. take their maximum or minimum value simultaneously for all centrality and $p_T$ selections. In addition, there are also $p_T$ dependent systematic errors, which are given in Table 1. The systematic errors do not alter the trends in the data.
We report the measurement of direct photons at midrapidity in Au+Au collisions at sqrt{s_NN} = 200 GeV. The direct photon signal was extracted for the transverse-momentum range of 4 GeV/c < p_T < 22 GeV/c, using a statistical method to subtract decay photons from the inclusive-photon sample. The direct-photon nuclear-modification factor R_AA was calculated as a function of p_T for different Au+Au collision centralities using the measured p+p direct-photon spectrum and compared to theoretical predictions. R_AA was found to be consistent with unity for all centralities over the entire measured p_T range. Theoretical models that account for modifications of initial-direct-photon production due to modified-parton-distribution functions in Au and the different isospin composition of the nuclei, predict a modest change of R_AA from unity and are consistent with the data. Models with compensating effects of the quark-gluon plasma on high-energy photons, such as suppression of jet-fragmentation photons and induced-photon bremsstrahlung from partons traversing the medium, are also consistent with this measurement.
We present measurements of azimuthal correlations of charged hadron pairs in $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions after subtracting an underlying event using a model that includes higher-order azimuthal anisotropy $v_2$, $v_3$, and $v_4$. After subtraction, the away-side ($\Delta\phi\sim\pi)$ of the highest transverse-momentum trigger ($p_T>4$ GeV/$c$) correlations is suppressed compared to that of correlations measured in $p$$+$$p$ collisions. At the lowest associated particle $p_T$, the away-side shape and yield are modified. These observations are consistent with the scenario of radiative-jet energy loss. For the lowest-$p_T$ trigger correlations, an away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle $\Psi_n$. The angular correlations show an asymmetry when selecting the sign of the trigger-particle azimuthal angle with respect to the $\Psi_2$ event plane. This asymmetry and the measured suppression of the pair yield out of plane is consistent with a path-length-dependent energy loss. No $\Psi_3$ dependence can be resolved within experimental uncertainties.
Higher-order flow harmonics for charged hadrons at midrapidity in Au$+$Au collisions at $\sqrt{s_{NN}}$ and their systematics: $v_2$, $v_3$, $v_4$, and $v_4\{\Psi_2\}$. The source of systematic uncertainties are difference among RXN event-planes, matching cut width for CNT hadron tracks, and difference between $v_n$ measured with RXN and BBC event planes .
Per-trigger yields $Y(\Delta\phi)$ of dihadrons pairs measured in Au$+$Au collisions at$\sqrt{s_{NN}}$ after subtracting the underlying event model with several $p_T$ selections and centralities. Systematic uncertainties are due to track matching and the $v_n$ and due to ZYAM.
Per-trigger yields $Y(\Delta\phi)$ of dihadron pairs measured in Au$+$Au collisions after subtracting the underlying event-model with several $p_T$ selections of the trigger and associated particles ($p_T^{t,a}$ and several centralities. Systematic uncertainties are due to track matching and the $v_n$ and due to ZYAM.
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has performed systematic measurements of phi meson production in the K+K- decay channel at midrapidity in p+p, d+Au, Cu+Cu and Au+Au collisions at sqrt(S_NN)=200 GeV. Results are presented on the phi invariant yield and the nuclear modification factor R_AA for Au+Au and Cu+Cu, and R_dA for d+Au collisions, studied as a function of transverse momentum (1<p_T<7 GeV/c) and centrality. In central and mid-central Au+Au collisions, the R_AA of phi exhibits a suppression relative to expectations from binary scaled p+p results. The amount of suppression is smaller than that of the neutral pion and the eta meson in the intermediate p_T range (2--5 GeV/c); whereas at higher p_T the phi, pi^0, and eta show similar suppression. The baryon (protons and anti-protons) excess observed in central Au+Au collisions at intermediate p_T is not observed for the phi meson despite the similar mass of the proton and the phi. This suggests that the excess is linked to the number of constituent quarks rather than the hadron mass. The difference gradually disappears with decreasing centrality and for peripheral collisions the R_AA values for both particles are consistent with binary scaling. Cu+Cu collisions show the same yield and suppression as Au+Au collisions for the same number of N_part. The R_dA of phi shows no evidence for cold nuclear effects within uncertainties.
Invariant $p_T$ spectra of the $\phi$ meson for different centrality bins in Au+Au, Cu+Cu, $d$+Au, and $p$+$p$ collisions at $\sqrt{s_{NN}}$ = 200 GeV.
$R_{AA}$ vs. $p_T$ for $\phi$ in central Au+Au collisions, $R_{AA}$ vs. $p_T$ for $\phi$ and $\pi^0$ in 10-20% mid-central Au+Au collisions, and $R_{AA}$ vs. $p_T$ for $\phi$ and $p$+$\bar{p}$ in 60-92% and for $\pi^0$ in 80-92% peripheral Au+Au collisions. The global uncertainty of ~ 10% related to the $p$+$p$ reference normalization is not shown.
$R_{AA}$ vs. $p_T$ for $\phi$ for 30-40% centrality Au+Au and 0-10% centrality Cu+Cu collisions, and $R_{AA}$ vs. $p_T$ for $\phi$ and $\pi^0$ for 40-50% centrality Au+Au and 10-20% centrality Cu+Cu collisions. The global uncertainty of ~ 10% related to the $p$+$p$ reference normalization is not shown.
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.
Heavy-flavor $e^{\pm}$ $v_2$ from Au+Au collisions, for the centralities indicated.
Nonphotonic electron $v_2$ as a function of $p_T$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
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