J/Psi production in p+p collisions at sqrt(s) = 200 GeV has been Measured in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) over a rapidity range of -2.2 < y < 2.2 and a ...transverse momentum range of 0 < pT < 9 GeV/c. The statistics available allow a detailed measurement of both the pT and rapidity distributions and are sufficient to constrain production models. The total cross section times branching ratio determined for J/Psi production is B_{ll} sigma_pp^J/psi = 178 +/- 3(stat) +/- 53(syst) +/- 18(norm) nb.
Differential elliptic flow (v_2) for phi mesons and (anti)deuterons (d^bar)d is measured for Au+Au collisions at sqrt(s_NN) = 200 GeV. The v_2 for phi mesons follows the trend of lighter pi^+/- and ...K^+/- mesons, suggesting that ordinary hadrons interacting with standard hadronic cross sections are not the primary driver for elliptic flow development. The v_2 values for (d^bar)d suggest that elliptic flow is additive for composite particles. This further validation of the universal scaling of v_2 per constituent quark for baryons and mesons suggests that partonic collectivity dominates the transverse expansion dynamics.
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.
Correlations between p and pbar's at transverse momenta typical of enhanced baryon production in Au+Au collisions are reported. The PHENIX experiment measures same and opposite sign baryon pairs in ...Au+Au collisions at sqrt(s_NN) = 200 GeV. Correlated production of p and p^bar with the trigger particle from the range 2.5 < p_T < 4.0 GeV/c and the associated particle with 1.8 < p_T < 2.5 GeV/c is observed to be nearly independent of the centrality of the collisions. Same sign pairs show no correlation at any centrality. The conditional yield of mesons triggered by baryons (and anti-baryons) and mesons in the same pT range rises with increasing centrality, except for the most central collisions, where baryons show a significantly smaller number of associated mesons. These data are consistent with a picture in which hard scattered partons produce correlated p and p^bar in the p_T region of the baryon excess.
Results from the PHENIX experiment of measurements of high-\(p_{\rm T}\) particle production presented at the Hard Probes 2004 Conference are summarized. This paper focuses on a sub-set of the ...measurements presented at the conference, namely the suppression of \(\pi^0\) production at moderate to high \(p_{\rm T}\) as a function of angle with respect to the collision reaction plane, \(\Delta\phi\), for different collision centralities. The data are presented in the form of nuclear modification factor as a function of angle with respect to the reaction plane, \(R_{AA} (\Delta \phi)\). The data are analyzed using empirical estimates of the medium-induced energy loss obtained from the \(R_{AA} (\Delta \phi)\) values. A geometric analysis is performed with the goal of understanding the simultaneous dependence of RAA on \(\Delta\phi\) and centrality. We find that the centrality and \(\Delta\phi\) dependence of the \(\pi^0\) suppression can be made approximately consistent using an admittedly over-simplistic description of the geometry of the jet propagation in the medium but only if the energy loss is effectively reduced for short parton path lengths in the medium. We find that with a more "canonical" treatment of the quenching geometry, the \(\pi^0\) suppression varies more rapidly with \(\Delta\phi\) than would be expected from the centrality dependence of the suppression.
Measurements of neutral pion production at midrapidity in {radical}(s{sub NN}) = 200 GeV Au+Au collisions as a function of transverse momentum, p{sub T}, collision centrality, and angle with respect ...to reaction plane are presented. The data represent the final {pi}{sup 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{sub T} > 6 GeV/c. We evaluate the suppression in the yield of high-p{sub T} {pi}{sup 0}'s relative to point-like scaling expectations using the nuclear modification factor R{sub AA}. We present the p{sub T} dependence of R{sub AA} for nine bins in collision centrality. We separately integrate R{sub AA} over larger p{sub T} bins to show more precisely the centrality dependence of the high-p{sub T} suppression. We then evaluate the dependence of the high-p{sub 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{sub T} {pi}{sup 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}{sup 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}{sup 0} suppression in different p{sub 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.
The second Fourier component v(2) of the azimuthal anisotropy with respect to the reaction plane is measured for direct photons at midrapidity and transverse momentum (p(T)) of 1-12 GeV/c in Au + Au ...collisions at √s(NN) = 200 GeV. Previous measurements of this quantity for hadrons with p(T) < 6 GeV/c indicate that the medium behaves like a nearly perfect fluid, while for p(T) > 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement with the PHENIX detector at the Relativistic Heavy Ion Collider we find that for p(T) > 4 GeV/c the anisotropy for direct photons is consistent with zero, which is as expected if the dominant source of direct photons is initial hard scattering. However, in the p(T) < 4 GeV/c region dominated by thermal photons, we find a substantial direct-photon v(2) comparable to that of hadrons, whereas model calculations for thermal photons in this kinematic region underpredict the observed v(2).
We present results on charged particle (
dN
ch
/
dη) and transverse energy densities (
dE
T/
dη) measured at mid-rapidity in Au
Au collisions at
S
N
N
=
200
GeV. The mean transverse energy per ...charged particle is derived. The results are presented as a function of centrality, which is defined by the number of participating nucleons (
N
p
), and compared to results obtained in Au
Au collisions at
S
N
N
=
130
GeV. A comparison with calculations from various theoretical models is performed.
Phys. Rev. C 107, 014907 (2023) The PHENIX experiment reports systematic measurements at the Relativistic
Heavy Ion Collider of $\phi$-meson production in asymmetric Cu$+$Au collisions
at ...$\sqrt{s_{_{NN}}}$=200 GeV and in U$+$U collisions at $\sqrt{s_{_{NN}}}$=193
GeV. Measurements were performed via the $\phi\rightarrow K^{+}K^{-}$ decay
channel at midrapidity $|\eta|<0.35$. Features of $\phi$-meson production
measured in Cu$+$Cu, Cu$+$Au, Au$+$Au, and U$+$U collisions were found to not
depend on the collision geometry, which was expected because the yields are
averaged over the azimuthal angle and follow the expected scaling with
nuclear-overlap size. The elliptic flow of the $\phi$ meson in Cu$+$Au,
Au$+$Au, and U$+$U collisions scales with second-order-participant eccentricity
and the length scale of the nuclear-overlap region (estimated with the number
of participating nucleons). At moderate $p_T$, $\phi$-meson production measured
in Cu$+$Au and U$+$U collisions is consistent with coalescence-model
predictions, whereas at high $p_T$ the production is in agreement with
expectations for in-medium energy loss of parent partons prior to their
fragmentation. The elliptic flow for $\phi$ mesons measured in Cu$+$Au and
U$+$U collisions is well described by a (2+1)D viscous-hydrodynamic model with
specific-shear viscosity $\eta/s=1/4\pi$.
Recent results on low mass dilepton measurements from the PHENIX experiment are reported. Invariant mass spectra of \(\phi\rightarrow e^ + e^-\) are measured for the first time in Au-Au collisions at ...\(\sqrt{s_{NN}} = 200\) GeV in Run2. In d-Au collisions, the yields and MT slopes of both \(\phi\rightarrow e^ + e^-\) and \(\phi \rightarrow K^ + K^-\) are measured. Both results are consistent with each other within errors. In the future, a Hadron Blind Detector will be installed in PHENIX which will enhance our capabilities of rejecting external photon conversions and Dalitz pairs, that will result in a significant reduction of the large combinatorial background.
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