1,721,471 research outputs found
Beam Energy and Centrality Dependence of Direct-Photon Emission from Ultrarelativistic Heavy-Ion Collisions
No full textThe PHENIX collaboration presents first measurements of low-momentum (0.41 GeV/c) direct-photon yield dNdirγ/dη is a smooth function of dNch/dη and can be well described as proportional to (dNch/dη)α with α≈1.25. This scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and the Large Hadron Collider, for centrality selected samples, as well as for different A+A collision systems. At a given beam energy, the scaling also holds for high pT (>5 GeV/c), but when results from different collision energies are compared, an additional √sNN-dependent multiplicative factor is needed to describe the integrated-direct-photon yield.peerReviewe
Bylaws of the PHENIX Collaboration
No full textThis paper contains the bylaws of the PHENIX Collaboration.
Adopted 9/1/1994; Revised: 1/11/96, 10/22/97, 9/9/99, 6/8/00, 6/13/03, 7/19/08, 12/11/08, 2/17/11, 1/9/13, 4/29/1
Measurement of jet-medium interactions via direct photon-hadron correlations in Au+Au and d+Au collisions at √sNN = 200 GeV
No full textWe present direct photon-hadron correlations in 200 GeV/A Au+Au, d+Au, and p+p collisions, for direct photon pT from 5–12 GeV/c, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in d+Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au+Au compared to p+p and d+Au. As the momentum fraction decreases, the yield of hadrons in Au+Au increases to an excess over the yield in p+p collisions. The excess is at large angles and at low hadron pT and is most pronounced for hadrons associated with lower momentum direct photons. Comparison to theoretical calculations suggests that the hadron excess arises from medium response to energy deposited by jets.peerReviewe
Hydrodynamic flow and jet induced mach shocks at RHIC and LHC
No full textWe discuss the present collective flow signals for the phase transition to quark-gluon plasma (QGP) and the collective flow as a barometer for the equation of state (EoS). A study of Mach shocks induced by fast partonic jets propagating through the QGP is given. We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies as compared to the case of jet propagation in a static medium. Results of a hydrodynamical study of jet energy loss are presented
Single electron yields from semileptonic charm and bottom hadron decays in Au+Au collisions at √sNN = 200 GeV
No full textThe PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open heavy flavor production
in minimum bias Au + Au collisions at √sNN = 200 GeV via the yields of electrons from semileptonic decays
of charm and bottom hadrons. Previous heavy flavor electron measurements indicated substantial modification
in the momentum distribution of the parent heavy quarks owing to the quark-gluon plasma created in these
collisions. For the first time, using the PHENIX silicon vertex detector to measure precision displaced tracking,
the relative contributions from charm and bottom hadrons to these electrons as a function of transverse momentum
are measured in Au + Au collisions. We compare the fraction of electrons from bottom hadrons to previously
published results extracted from electron-hadron correlations in p + p collisions at √sNN = 200 GeV and find
the fractions to be similar within the large uncertainties on both measurements for pT > 4 GeV/c. We use the
bottom electron fractions in Au + Au and p + p along with the previously measured heavy flavor electron RAA
to calculate the RAA for electrons from charm and bottom hadron decays separately. We find that electrons from
bottom hadron decays are less suppressed than those from charm for the region 3 < pT < 4 GeV/c.peerReviewe
Systematic study of nuclear effects in p+Al, p+Au, d+Au, and 3He+Au collisions at √sNN = 200 GeV using π0 production
No full textThe PHENIX Collaboration presents a systematic study of inclusive π0 production from p+p, p+Al, p+Au, d+Au, and 3He+Au collisions at √sNN = 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, RxA, are consistent with unity for pT above 8GeV/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-pT−π0 production, the nucleons in the d and 3He interact mostly independently with the Au nucleus and that the counterintuitive 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 pT 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>3He+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 pT.peerReviewe
Low-pT direct-photon production in Au+Au collisions at √sNN = 39 and 62.4 GeV
No full textThe measurement of direct photons from Au+Au collisions at √sNN=39 and 62.4 GeV in the transverse-momentum range 0.4<3Gev/c is presented by the PHENIX collaboration at the BNLRelativistic Heavy Ion Collider. A significant direct-photon yield is observed in both collision systems. A universal scaling is observed when the direct-photon pT spectra for different center-of-mass energies and for different centrality selections at √sNN=62.4 GeV is scaled with (dNch/dη)α for α=1.21±0.04. This scaling also holds true for direct-photon spectra from Au+Au collisions at √sNN=200 GeV measured earlier by PHENIX, as well as the spectra from Pb+Pb at √sNN=2760 GeV published by ALICE. The scaling power α seems to be independent of pT, center of mass energy, and collision centrality. The spectra from different collision energies have a similar shape up to pT of 2 Gev/c. The spectra have a local inverse slope Teff increasing with pT of 0.174±0.018Gev/c in the range 0.4<1.3Gev/c and increasing to 0.289±0.024Gev/c for 0.9<2.1Gev/c. The observed similarity of low-pT direct-photon production from √sNN=39 to 2760 GeV suggests a common source of direct photons for the different collision energies and event centrality selections, and suggests a comparable space-time evolution of direct-photon emission.peerReviewe
Nonprompt direct-photon production in Au+Au collisions at √sNN = 200 GeV
No full textThe measurement of the direct-photon spectrum from Au+Au collisions at √sNN=200 −−−√=200 GeV is presented by the PHENIX collaboration using the external-photon-conversion technique for 0\%--93\% central collisions in a transverse-momentum (pT) range of 0.8--10 GeV/c. An excess of direct photons, above prompt-photon production from hard-scattering processes, is observed for pT<6 GeV/c. Nonprompt direct photons are measured by subtracting the prompt component, which is estimated as Ncoll-scaled direct photons from p+p collisions at 200 GeV, from the direct-photon spectrum. Results are obtained for 0.8<6.0 GeV/c and suggest that the spectrum has an increasing inverse slope from ≈0.2 to 0.4 GeV/c with increasing pT, which indicates a possible sensitivity of the measurement to photons from earlier stages of the evolution of the collision. In addition, like the direct-photon production, the pT-integrated nonprompt direct-photon yields also follow a power-law scaling behavior as a function of collision-system size. The exponent, α, for the nonprompt component is found to be consistent with 1.1 with no apparent pT dependence.peerReviewe
Measurements of second-harmonic Fourier coefficients from azimuthal anisotropies in p+p, p+Au, d+Au, and 3He+Au collisions at √sNN = 200 GeV
No full textRecently, the PHENIX Collaboration has published second- and third-harmonic Fourier coefficients v2 and v3 for midrapidity (|η|<0.35) charged hadrons in 0%–5% central p+Au, d+Au, and 3He+Au collisions at √sNN=200 GeV, utilizing three sets of two-particle correlations for two detector combinations with different pseudorapidity acceptance [Acharya et al., Phys. Rev. C 105, 024901 (2022)]. This paper extends these measurements of v2 to all centralities in p+Au, d+Au, and 3He+Au collisions, as well as p+p collisions, as a function of transverse momentum (pT) and event multiplicity. The kinematic dependence of v2 is quantified as the ratio R of v2 between the two detector combinations as a function of event multiplicity for 0.5<1 and 2<2.5GeV/c. A multiphase-transport (AMPT) model can reproduce the observed v2 in most-central to midcentral d+Au and 3He+Au collisions. However, the AMPT model systematically overestimates the measurements in p+p, p+Au, and peripheral d+Au and 3He+Au collisions, indicating a higher nonflow contribution in the AMPT model than in the experimental data. The AMPT model fails to describe the observed R for 0.5<1GeV/c, but there is qualitative agreement with the measurements for 2<2.5GeV/c.peerReviewe
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