Acharya, U. A.*; 長谷川 勝一; 今井 憲一*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他306名*
Physical Review Letters, 127(16), p.162001_1 - 162001_8, 2021/10
Studying spin-momentum correlations in hadronic collisions offers a glimpse into a three-dimensional picture of proton structure. The transverse single-spin asymmetry for midrapidity isolated direct photons in collisions at =200 GeV is measured with the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). Because direct photons in particular are produced from the hard scattering and do not interact via the strong force, this measurement is a clean probe of initial-state spin-momentum correlations inside the proton and is in particular sensitive to gluon interference effects within the proton. This is the first time direct photons have been used as a probe of spin-momentum correlations at RHIC. The uncertainties on the results are a fifty-fold improvement with respect to those of the one prior measurement for the same observable, from the Fermilab E704 experiment. These results constrain gluon spin-momentum correlations in transversely polarized protons.
Acharya, U. A.*; 長谷川 勝一; 今井 憲一*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他309名*
Physical Review D, 103(5), p.052009_1 - 052009_10, 2021/03
We present a measurement of the transverse single-spin asymmetry for and mesons in collisions in the pseudorapidity range and at a center-of-mass energy of 200 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. In comparison with previous measurements in this kinematic region, these results have a factor of 3 smaller uncertainties. As hadrons, and mesons are sensitive to both initial- and final-state nonperturbative effects for a mix of parton flavors. Comparisons of the differences in their transverse single-spin asymmetries have the potential to disentangle the possible effects of strangeness, isospin, or mass. These results can constrain the twist-3 trigluon collinear correlation function as well as the gluon Sivers function.
Acharya, U. A.*; 長谷川 勝一; 今井 憲一*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他308名*
Physical Review D, 103(3), p.032007_1 - 032007_8, 2021/02
In 2015, the PHENIX collaboration has measured very forward () single-spin asymmetries of inclusive neutrons in transversely polarized proton-proton and proton-nucleus collisions at a center of mass energy of 200 GeV. A previous publication from this data set concentrated on the nuclear dependence of such asymmetries. In this measurement the explicit transverse-momentum dependence of inclusive neutron single spin asymmetries for proton-proton collisions is extracted using a bootstrapping-unfolding technique on the transverse momenta. This explicit transverse-momentum dependence will help improve the understanding of the mechanisms that create these asymmetries.
Acharya, U.*; 長谷川 勝一; 今井 憲一*; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他397名*
Physical Review C, 102(6), p.064905_1 - 064905_13, 2020/12
The PHENIX experiment at the Relativistic Heavy Ion Collider measured and mesons at midrapidity in UU collisions at GeV in a wide transverse momentum range. Measurements were performed in the decay modes. A strong suppression of and meson production at high transverse momentum was observed in central UU collisions relative to binary scaled results. Yields of and mesons measured in UU collisions show similar suppression pattern to the ones measured in AuAu collisions at GeV for similar numbers of participant nucleons. The / ratios do not show dependence on centrality or transverse momentum, and are consistent with previously measured values in hadron-hadron, hadron-nucleus, nucleus-nucleus, and collisions.
Acharya, U.*; 長谷川 勝一; 今井 憲一*; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他572名*
Physical Review C, 102(5), p.054910_1 - 054910_11, 2020/11
We present direct photon-hadron correlations in 200 GeV/A AuAu, Au and collisions, for direct photon from 5 - 12 GeV/, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in 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 AuAu compared to and Au. As the momentum fraction decreases, the yield of hadrons in AuAu increases to an excess over the yield in collisions. The excess is at large angles and at low hadron 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.
Acharya, U.*; 長谷川 勝一; 今井 憲一*; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他344名*
Physical Review D, 102(9), p.092002_1 - 092002_14, 2020/11
The cross section of bottom quark-antiquark () production in collisions at GeV is measured with the PHENIX detector at the Relativistic Heavy Ion Collider. The results are based on the yield of high mass, like-sign muon pairs measured within the PHENIX muon arm acceptance (). The signal is extracted from like-sign dimuons by utilizing the unique properties of neutral meson oscillation. We report a differential cross section of nb for like-sign muons in the rapidity and ranges and GeV/, and dimuon mass of 5 - 10 GeV/. The extrapolated total cross section at this energy for production is b. The total cross section is compared to a perturbative quantum chromodynamics calculation and is consistent within uncertainties. The azimuthal opening angle between muon pairs from decays and their distributions are compared to distributions generated using , which includes next-to-leading order processes. The azimuthal correlations and pair distribution are not very well described by calculations, but are still consistent within uncertainties. Flavor creation and flavor excitation subprocesses are favored over gluon splitting.
Acharya, U.*; 長谷川 勝一; 今井 憲一*; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他344名*
Physical Review D, 102(7), p.072008_1 - 072008_13, 2020/10
The PHENIX experiment has measured the spin alignment for inclusive decays in collisions at GeV at midrapidity. The angular distributions have been measured in three different polarization frames, and the three decay angular coefficients have been extracted in a full two-dimensional analysis. Previously, PHENIX saw large longitudinal net polarization at forward rapidity at the same collision energy. This analysis at midrapidity, complementary to the previous PHENIX results, sees no sizable polarization in the measured transverse momentum range of GeV/. The results are consistent with a previous one-dimensional analysis at midrapidity at GeV. The transverse-momentum-dependent cross section for midrapidity production has additionally been measured, and after comparison to world data we find a simple logarithmic dependence of the cross section on .
Acharya, U.*; 長谷川 勝一; 今井 憲一*; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他354名*
Physical Review D, 102(3), p.032001_1 - 032001_9, 2020/08
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the longitudinal double spin asymmetries, , for charged pions at midrapidity () in longitudinally polarized collisions at GeV. These measurements are sensitive to the gluon spin contribution to the total spin of the proton in the parton momentum fraction range between 0.04 and 0.09. One can infer the sign of the gluon polarization from the ordering of pion asymmetries with charge alone. The asymmetries are found to be consistent with global quantum-chromodynamics fits of deep-inelastic scattering and data at GeV, which show a nonzero positive contribution of gluon spin to the proton spin.
Acharya, U.*; 長谷川 勝一; 今井 憲一*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他358名*
Physical Review C, 102(1), p.014902_1 - 014902_23, 2020/07
Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of harmonium in small systems have become increasingly relevant. We present the results of measurements at forward and backward rapidity in various small collision systems, , Al, Au and HeAu, at =200 GeV. The results are presented in the form of the observable , the nuclear modification factor, a measure of the ratio of the invariant yield compared to the scaled yield in collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on production with different projectile sizes and He, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for Au and HeAu. However, for 0% - 20% central collisions at backward rapidity, the modification for HeAu is found to be smaller than that for Au, with a mean fit to the ratio of (stat)(syst), possibly indicating final state effects due to the larger projectile size.
Aidala, C.*; 長谷川 勝一; 今井 憲一*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他297名*
Physical Review C, 101(3), p.034910_1 - 034910_16, 2020/03
The PHENIX experiment has studied nuclear effects in Al and Au collisions at GeV on charged hadron production at forward rapidity (, -going direction) and backward rapidity (, -going direction). Such effects are quantified by measuring nuclear modification factors as a function of transverse momentum and pseudorapidity in various collision multiplicity selections. In central Al and Au collisions, a suppression (enhancement) is observed at forward (backward) rapidity compared to the binary scaled yields in + collisions. The magnitude of enhancement at backward rapidity is larger in Au collisions than in Al collisions, which have a smaller number of participating nucleons. However, the results at forward rapidity show a similar suppression within uncertainties. The results in the integrated centrality are compared with calculations using nuclear parton distribution functions, which show a reasonable agreement at the forward rapidity but fail to describe the backward rapidity enhancement.
Acharya, U. A.*; 長谷川 勝一; 今井 憲一*; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他353名*
Physical Review D, 101(5), p.052006_1 - 052006_13, 2020/03
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section, mean transverse momentum, mean transverse momentum squared of inclusive and cross-section ratio of to at forward rapidity in collisions at GeV via the dimuon decay channel. Comparison is made to inclusive cross sections measured at GeV and 2.76 - 13 TeV. The result is also compared to leading-order nonrelativistic QCD calculations coupled to a color-glass-condensate description of the low- gluons in the proton at low transverse momentum () and to next-to-leading order nonrelativistic QCD calculations for the rest of the range. These calculations overestimate the data at low . While consistent with the data within uncertainties above GeV/, the calculations are systematically below the data. The total cross section times the branching ratio is BR GeV/) = 54.3 0.5 (stat) 5.5 (syst) nb.
Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他296名*
Physical Review Letters, 123(12), p.122001_1 - 122001_9, 2019/09
We report on the nuclear dependence of transverse single-spin asymmetries (TSSAs) in the production of positively-charged hadrons in polarized , Al and Au collisions at GeV. The measurements have been performed at forward rapidity () over the range of GeV and . We observed a positive asymmetry for positively-charged hadrons in collisions, and a significantly reduced asymmetry in + collisions. These results reveal a nuclear dependence of charged hadron in a regime where perturbative techniques are relevant. These results provide new opportunities to use A collisions as a tool to investigate the rich phenomena behind TSSAs in hadronic collisions and to use TSSA as a new handle in studying small-system collisions.
Adare, A.*; 長谷川 勝一; 今井 憲一; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他666名*
Physical Review Letters, 123(2), p.022301_1 - 022301_10, 2019/07
The PHENIX collaboration presents first measurements of low-momentum (0.4 3 GeV/) direct-photon yields from AuAu collisions at = 39 and 62.4 GeV. For both beam energies the direct-photon yields are substantially enhanced with respect to expectations from prompt processes, similar to the yields observed in AuAu collisions at = 200. Analyzing the photon yield as a function of the experimental observable reveals that the low-momentum (1 GeV/) direct-photon yield is a smooth function of and can be well described as proportional to with 1.25. This new scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and Large Hadron Collider, for centrality selected samples, as well as for different, collision systems. At a given beam energy the scaling also holds for high (5 GeV/) but when results from different collision energies are compared, an additional -dependent multiplicative factor is needed to describe the integrated-direct-photon yield.
Adare, A.*; 長谷川 勝一; 今井 憲一; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他451名*
Physical Review C, 99(5), p.054903_1 - 054903_29, 2019/05
We present measurements of azimuthal correlations of charged hadron pairs in GeV AuAu collisions after subtracting an underlying event using a model that includes higher-order azimuthal anisotropy , , and . After subtraction, the away-side ( of the highest transverse-momentum trigger ( GeV/) correlations is suppressed compared to that of correlations measured in collisions. At the lowest associated particle , the away-side shape and yield are modified. These observations are consistent with the scenario of radiative-jet energy loss. For the lowest- 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 . The angular correlations show an asymmetry when selecting the sign of the trigger-particle azimuthal angle with respect to the 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 dependence can be resolved within experimental uncertainties.
Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他296名*
Physical Review D, 99(9), p.092003_1 - 092003_21, 2019/05
Measurements of the differential production of electrons from open-heavy-flavor hadrons with charm- and bottom-quark content in collisions at GeV are presented. The measurements proceed through displaced-vertex analyses of electron tracks from the semileptonic decay of charm and bottom hadrons using the PHENIX silicon-vertex detector. The relative contribution of electrons from bottom decays to inclusive heavy-flavor-electron production is found to be consistent with fixed-order-plus-next-to-leading-log perturbative-QCD calculations within experimental and theoretical uncertainties. These new measurements in collisions provide a precision baseline for comparable forthcoming measurements in AA collisions.
Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他293名*
Physical Review C, 99(4), p.044912_1 - 044912_10, 2019/04
The PHENIX collaboration has measured high- dihadron correlations in , Al, and Au collisions at GeV. The correlations arise from inter- and intra-jet correlations and thus have sensitivity to nonperturbative effects in both the initial and final states. The distributions of , the transverse momentum component of the associated hadron perpendicular to the trigger hadron, are sensitive to initial and final state transverse momenta. These distributions are measured multi-differentially as a function of , the longitudinal momentum fraction of the associated hadron with respect to the trigger hadron. The near-side widths, sensitive to fragmentation transverse momentum, show no significant broadening between Au, Al, and . The away-side nonperturbative widths are found to be broadened in Au when compared to ; however, there is no significant broadening in Al compared to collisions. The data also suggest that the away-side broadening is a function of , the number of binary nucleon-nucleon collisions, in the interaction. The potential implications of these results with regard to initial and final state transverse momentum broadening and energy loss of partons in a nucleus, among other nuclear effects, are discussed.
Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他287名*
Physical Review D, 99(7), p.072003_1 - 072003_41, 2019/04
PHENIX reports differential cross sections of pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in collisions at GeV at forward and backward rapidity (). The pairs from , , and Drell-Yan are separated using a simultaneous fit to unlike- and like-sign muon pair spectra in mass and . The azimuthal opening angle correlation between the muons from and decays and the pair- distributions are compared to distributions generated using and models, which both include next-to-leading order processes. The measured distributions for pairs from are consistent with calculations. The data presents narrower azimuthal correlations and softer distributions compared to distributions generated from . The data are well described by both models. The extrapolated total cross section for bottom production is [b], which is consistent with previous measurements at the Relativistic Heavy Ion Collider in the same system at the same collision energy, and is approximately a factor of two higher than the central value calculated with theoretical models. The measured Drell-Yan cross section is in good agreement with next-to-leading-order quantum-chromodynamics calculations.
Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他312名*
Nature Physics, 15(3), p.214 - 220, 2019/03
Experimental studies of the collisions of heavy nuclei at relativistic energies have established the properties of the quark-gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons. In this state, matter behaves as a nearly inviscid fluid that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the particles produced, creating a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton-proton and proton-nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton-gold (p+Au), deuteron-gold (d+Au) and helium-gold (He+Au) collisions at a nucleon-nucleon centre-of-mass energy = 200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide the best simultaneous description of these measurements.
Adare, A.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他317名*
Physical Review C, 99(2), p.024903_1 - 024903_16, 2019/02
We present measurements of elliptic and triangular azimuthal anisotropy of charged particles detected at forward rapidity in AuAu collisions at GeV, as a function of centrality. The multiparticle cumulant technique is used to obtain the elliptic flow coefficients , , , and , and triangular flow coefficients and . Using the small-variance limit, we estimate the mean and variance of the event-by-event distribution from and . In a complementary analysis, we also use a folding procedure to study the distributions of and directly, extracting both the mean and variance. Implications for initial geometrical fluctuations and their translation into the final state momentum distributions are discussed.
Adare, A.*; 長谷川 勝一; 今井 憲一; 永宮 正治; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他448名*
Physical Review C, 98(5), p.054902_1 - 054902_11, 2018/11
We have measured direct photons for GeV/ in minimum bias and 0% - 40% most central events at midrapidity for CuCu collisions at GeV. The contribution from quasi-real direct virtual photons has been determined as an excess over the known hadronic contributions in the mass distribution. A clear enhancement of photons over the binary scaled fit is observed for GeV/ in CuCu data. The spectra are consistent with the AuAu data covering a similar number of participants. The inverse slopes of the exponential fits to the excess after subtraction of the baseline are 28553(stat)57(syst)~MeV/ and 33372(stat)45(syst)~MeV/ for minimum bias and 0% - 40% most central events, respectively. The rapidity density, , of photons demonstrates the same power law as a function of observed in AuAu at the same collision energy.