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.
Aidala, C.*; 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, 98(5), p.054903_1 - 054903_11, 2018/11
Production of and mesons has been measured at midrapidity in CuAu collisions at =200 GeV. Measurements were performed in decay channel in the 1(2)-20 GeV/ transverse momentum range. A strong suppression is observed for and meson production at high transverse momentum in central CuAu collisions relative to the results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to AuAu with comparable nuclear overlap. The ratio measured as a function of transverse momentum is consistent with -scaling parameterization down to 2 GeV/, its asymptotic value is constant and consistent with AuAu and and does not show any significant dependence on collision centrality. Similar results were obtained in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions as well as in collisions in a range of collision energies 3-1800 GeV. This suggests that the quark-gluon-plasma medium produced in CuCu collisions either does not affect the jet fragmentation into light mesons or it affects the and the same way.
Adare, A.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他362名*
Physical Review Letters, 121(22), p.222301_1 - 222301_8, 2018/11
Asymmetric nuclear collisions of +Al, +Au, +Au, and He+Au at = 200 GeV provide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.
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468名*
Physical Review C, 98(1), p.014912_1 - 014912_16, 2018/07
We present measurements of two-particle angular correlations between high-transverse-momentum ( GeV/) observed at midrapidity () and particles produced either at forward () or backward () rapidity in Au and collisions at GeV. The azimuthal angle correlations for particle pairs with this large rapidity gap in the Au-going direction exhibit a ridge-like structure that persists up to GeV/ and which strongly depends on collision centrality, which is a similar characteristic to the hydrodynamical particle flow in A+A collisions. The ridge-like structure is absent in the -going direction as well as in collisions, in the transverse-momentum range studied. The results indicate that the ridge-like structure is shifted in the Au-going direction toward more central collisions, similar to the charged-particle pseudorapidity distributions.
Adare, A.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他347名*
Physical Review C, 97, p.064904_1 - 064904_11, 2018/06
We present measurements of the transverse-momentum dependence of elliptic flow for identified pions and (anti)protons at midrapidity (), in 0% - 5% central + Au and He + Au collisions at = 200 GeV. When taken together with previously published measurements in + Au collisions at = 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 in + Au and He + Au collisions, just as in large nucleus-nucleus ( + ) collisions, and a smaller splitting in + Au collisions. Both hydrodynamic and transport model calculations successfully describe the data at low ( GeV/), but fail to describe various features at higher . In all systems, the values follow an approximate quark-number scaling as a function of the hadron transverse kinetic energy per constituent quark(), which was also seen previously in + collisions.
Adare, A.*; 長谷川 勝一; 永宮 正治; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他448名*
Physical Review C, 97(6), p.064911_1 - 064911_22, 2018/06
We present a detailed measurement of charged two-pion correlation functions in 0%-30% centrality GeV AuAu collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Lvy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter , the Lvy index of stability and the Lvy length scale parameter as a function of average transverse mass of the pair . We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same Lvy-stable source functions. The measurements indicate a decrease of the strength of the correlations at low . The Lvy length scale parameter decreases with increasing , following a hydrodynamically predicted type of scaling behavior. The values of the Lvy index of stability are found to be significantly lower than the Gaussian case of , but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.
Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他311名*
Physical Review Letters, 120(6), p.062302_1 - 062302_8, 2018/02
Recently, multiparticle-correlation measurements of relativistic HeAu, Pb, and even collisions have shown surprising collective signatures. Here we present beam-energy-scan measurements of 2-, 4-, and 6-particle angular correlations in Au collisions at =200, 62.4, 39, and 19.6 GeV. We also present measurements of 2- and 4-particle angular correlations in Au collisions at =200 GeV. We find the 4-particle cumulant to be real-valued for Au collisions at all four energies. We also find that the 4-particle cumulant in Au has the opposite sign as that in Au, indicating that the correlations are geometrical and therefore collective in origin. Further we find that the 6-particle cumulant agrees with the 4-particle cumulant in Au collisions at 200 GeV, which indicates that nonflow effects are subdominant and provides strong evidence of collectivity.
Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他456名*
Physical Review C, 96(6), p.064901_1 - 064901_18, 2017/12
The fraction of mesons which come from B-meson decay, , is measured for J/ rapidity and in + and Cu+Au collisions at =200 GeV with the PHENIX detector. The extracted fraction is = 0.025 0.006(stat) 0.010(syst) for + collisions. For Cu+Au collisions, is 0.094 0.028(stat) 0.037(syst) in the Au-going direction () and 0.089 0.026(stat) 0.040(syst) in the Cu-going direction (). The nuclear modification factor, , of B mesons in Cu+Au collisions is consistent with binary scaling of measured yields in + at both forward and backward rapidity.
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497名*
Physical Review C, 96(2), p.024907_1 - 024907_19, 2017/08
We report a measurement of pairs from semileptonic heavy-flavor decays in collisions at = 200 GeV. The pair yield from and is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and . We used three different event generators, , , and , to simulate the spectra from and production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to , significant differences are observed for the total cross section. These difference are less pronounced for than for . The same model dependence was observed in already published data. The data are also directly compared with data in mass and , and within the statistical accuracy no nuclear modification is seen.
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462名*
Physical Review D, 95(7), p.072002_1 - 072002_19, 2017/04
Dihadron and isolated direct photon-hadron angular correlations are measured in collisions at = 510 GeV. Correlations of charged hadrons of GeV/ with mesons of GeV/ or isolated direct photons of GeV/ 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 perpendicular to the axis of the trigger particle, which is the high- direct photon or . Nonperturbative evolution effects are extracted from Gaussian fits to the away-side inclusive-charged-hadron yields for different trigger-particle transverse momenta (). The Gaussian widths and root mean square of are reported as a function of the interaction hard scale to investigate possible transverse-momentum-dependent evolution differences between the - and direct photon- correlations and factorization breaking effects. The widths are found to decrease with , 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 collisions. This behavior is in contrast to Drell-Yan and semi-inclusive deep-inelastic scattering measurements.
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545名*
Physical Review C, 94(6), p.064901_1 - 064901_14, 2016/12
The PHENIX experiment at the BNL Relativistic Heavy Ion Collider has measured second- and third-order Fourier coefficients of the azimuthal distributions of direct photons emitted at midrapidity in Au+Au collisions at = 200 GeV for various collision centralities. Combining two different analysis techniques, results were obtained in the transverse momentum range of GeV/. At low the second-order coefficients, , are similar to the ones observed in hadrons. Third-order coefficients, , are nonzero and almost independent of centrality. These new results on and , 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.
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397名*
Physical Review C, 94(5), p.054910_1 - 054910_18, 2016/11
Measurements of anisotropic flow Fourier coefficients () for inclusive charged particles and identified hadrons , , , and produced at midrapidity in Cu+Au collisions at = 200 GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The particle azimuthal distributions with respect to different-order symmetry planes , for 1, 2, and 3 are studied as a function of transverse momentum over a broad range of collision centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three harmonics. The charged-particle results are compared with hydrodynamical and transport model calculations. We also compare these Cu+Au results with those in Cu+Cu and Au+Au collisions at the same and find that the and , as a function of transverse momentum, follow a common scaling with .
Adare, A.*; 今井 憲一; 永宮 正治; 谷田 聖; PHENIX Collaboration*; 他385名*
Physical Review C, 93(5), p.051902_1 - 051902_8, 2016/05
Measurements of the anisotropic flow coefficients , , , and , for identified particles (, , and ) at midrapidity, obtained relative to the event planes at forward rapidities in Au + Au collisions at 200 GeV, are presented as a function of collision centrality and particle transverse momenta . The coefficients show characteristic patterns consistent with hydrodynamical expansion of the matter produced in the collisions. For each harmonic , a modified valence quark-number scaling [plotting versus transverse kinetic energies ] is observed to yield a single curve for all the measured particle species for a broad range of . A simultaneous blast-wave model fit to the observed coefficients and published particle spectra identifies radial flow anisotropies and spatial eccentricities at freeze-out. These are generally smaller than the initial-state participant-plane geometric eccentricities as also observed in the final eccentricity from quantum interferometry measurements with respect to the event plane.
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397名*
Physical Review C, 93(3), p.034903_1 - 034903_12, 2016/03
The invariant yields, , for production at forward rapidity () in U+U collisions at = 193 GeV have been measured as a function of collision centrality. The invariant yields and nuclear-modification factor are presented and compared with those from Au + Au collisions in the same rapidity range. Additionally, the direct ratio of the invariant yields from U + U and Au + Au collisions within the same centrality class is presented, and used to investigate the role of coalescence. Two different parametrizations of the deformed Woods-Saxon distribution were used in Glauber calculations to determine the values of the number of nucleon-nucleon collisions in each centrality class, , and these were found to give significantly different values. Results using values from both deformed Woods-Saxon distributions are presented. The measured ratios show that the suppression, relative to binary collision scaling, is similar in U + U and Au + Au for peripheral and midcentral collisions, but that show less suppression for the most central U + U collisions. The results are consistent with a picture in which, for central collisions, increase in the yield due to coalescence becomes more important than the decrease in yield due to increased energy density. For midcentral collisions, the conclusions about the balance between coalescence and suppression depend on which deformed Woods-Saxon distribution is used to determine .
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426名*
Physical Review C, 93(3), p.034904_1 - 034904_29, 2016/03
The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open heavy flavor production in minimum bias Au + Au collisions at = 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 collisions at = 200 GeV and find the fractions to be similar within the large uncertainties on both measurements for 4 GeV/. We use the bottom electron fractions in Au + Au and along with the previously measured heavy flavor electron to calculate the 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 4 GeV/.
Adare, A.*; 今井 憲一; 長谷川 勝一; 永宮 正治; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他477名*
Physical Review Letters, 116(12), p.122301_1 - 122301_9, 2016/03
Jet production rates are measured in and Au collisions at = 200 GeV recorded in 2008 with the PHENIX detector at the Relativistic Heavy Ion Collider. Jets are reconstructed using the =0.3 anti- algorithm from energy deposits in the electromagnetic calorimeter and charged tracks in multiwire proportional chambers, and the jet transverse momentum () spectra are corrected for the detector response. Spectra are reported for jets with GeV/ within a pseudorapidity acceptance of . The nuclear-modification factor () values and central-to-peripheral ratios () show large, -dependent deviations from unity, challenging the conventional models that relate hard-process rates and soft-particle production in collisions involving nuclei.
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505名*
Physical Review C, 93(2), p.024904_1 - 024904_13, 2016/02
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured meson production and its nuclear modification in asymmetric Cu + Au heavy-ion collisions at = 200 GeV at both forward Cu-going direction (1.2 y 2.2) 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 meson yield integrated over 1 5 GeV/ 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 + Au collisions for these rapidities.
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699名*
Physical Review C, 93(2), p.024901_1 - 024901_30, 2016/02
Measurements of midrapidity charged-particle multiplicity distributions, , and midrapidity transverse-energy distributions, , are presented for a variety of collision systems and energies. Included are distributions for Au+Au collisions at d^3p + pN_N_N_N_dE_T/ddN_/deta$, the latter of which is seen to be constant as a function of centrality for all systems.
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623名*
Physical Review C, 93(2), p.024911_1 - 024911_20, 2016/02
Measurements of the fractional momentum loss () of high-transverse-momentum-identified hadrons in heavy-ion collisions are presented. Using in Au+Au and Cu+Cu collisions at = 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 as a function of a number of variables: the number of participants, , the number of quark participants, , the charged-particle density, , and the Bjorken energy density times the equilibration time, . We find that the , where has its maximum, varies both with centrality and collision energy. Above the maximum, tends to follow a power-law function with all four scaling variables. The data at = 200 and 2.76 TeV, for sufficiently high particle densities, have a common scaling of with and , lending insight into the physics of parton energy loss.
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440名*
Physical Review C, 93(1), p.014904_1 - 014904_34, 2016/01
We present measurements of production at midrapidity in Au + Au collisions at = 200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass ( GeV/) and pair transverse momentum ( GeV/) for minimum bias and for five centrality classes. The yield is compared to the expectations from known sources. In the low-mass region (0.30-0.76 GeV/) there is an enhancement that increases with centrality and is distributed over the entire pair range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to or to for minimum bias collisions when the open heavy-flavor contribution is calculated with pythia or mc@nlo, respectively. The inclusive mass and distributions, as well as the centrality dependence, are well reproduced by model calculations where the enhancement mainly originates from the melting of the meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region (1.2-2.8 GeV/), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.