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.
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 ( 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 (,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.
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; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他351名*
Physical Review D, 98(9), p.092006_1 - 092006_13, 2018/11
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of (1020) meson production at forward rapidity in collisions at 510 GeV via the dimuon decay channel. The integrated cross section in the rapidity and ranges and GeV/ is ~mb. The energy dependence of (; GeV/) is studied using the PHENIX measurements at 200 and 510 GeV and the Large-Hadron-Collider measurements at 2.76 and 7 TeV. The experimental results are compared to various event generator predictions (pythia6, pythia8, phojet, ampt, epos3, and epos-lhc).
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423名*
Physical Review D, 98(3), p.032007_1 - 032007_14, 2018/08
We have measured the cross section and single spin asymmetries from forward production in longitudinally polarized collisions at GeV using the PHENIX detector at the Relativistic Heavy Ion Collider. The cross sections are consistent with previous measurements at this collision energy, while the most forward and backward longitudinal single spin asymmetries provide new insights into the sea quark helicities in the proton. The charge of the bosons provides a natural flavor separation of the participating partons.
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; 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.
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.
本多 良太郎*; 長谷川 勝一; 早川 修平; 細見 健二; 市川 裕大; 今井 憲一; 永宮 正治; 佐甲 博之; 佐藤 進; 杉村 仁志; et al.
Physical Review C, 96(1), p.014005_1 - 014005_23, 2017/07
We searched for the bound state of the neutron-rich -hypernucleus H, using the Li double charge-exchange reaction at a beam momentum of 1.2 GeV/ at J-PARC. A total of was driven onto a Li target of 3.5 g/cm thickness. No event was observed below the bound threshold, i.e., the mass of H+, in the missing-mass spectrum of the Li reaction in the angular range. Furthermore, no event was found up to 2.8 MeV/c above the bound threshold.
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431名*
Physical Review D, 95(11), p.112001_1 - 112001_15, 2017/06
The cross section and transverse single-spin asymmetries of and from open heavy-flavor decays in polarized collisions at = 200 GeV were measured by the PHENIX experiment during 2012 at the Relativistic Heavy Ion Collider. Because heavy-flavor production is dominated by gluon-gluon interactions at = 200 GeV, these measurements offer a unique opportunity to obtain information on the trigluon correlation functions. The measurements are performed at forward and backward rapidity () over the transverse momentum range of GeV/ for the cross section and GeV/ for the asymmetry measurements. The obtained cross section is compared to a fixed-order-plus-next-to-leading-log perturbative-quantum-chromodynamics calculation. The asymmetry results are consistent with zero within uncertainties, and a model calculation based on twist-3 three-gluon correlations agrees with the data.
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425名*
Physical Review D, 95(9), p.092002_1 - 092002_18, 2017/05
We report the first measurement of the fraction of mesons coming from -meson decay () in collisions at GeV. The measurement is performed using the forward silicon vertex detector and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of due to -meson decays from prompt . The measured value of is for with transverse momenta GeV/ and rapidity . The measured fraction at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-to-leading-logarithm and color-evaporation-model predictions. The cross section per unit rapidity extracted from the obtained and the PHENIX inclusive cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean hadron rapidity in 510 GeV collisions, is b. It is consistent with the fixed-order-next-to-leading-logarithm calculations.
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389名*
Physical Review D, 95(9), p.092003_1 - 092003_13, 2017/05
We report the first measurement of the full angular distribution for inclusive decays in collisions at GeV. The measurements are made for transverse momentum GeV/ and rapidity in the Helicity, Collins-Soper, and Gottfried-Jackson reference frames. In all frames the polar coefficient is strongly negative at low and becomes close to zero at high , while the azimuthal coefficient is close to zero at low , and becomes slightly negative at higher . The frame-independent coefficient is strongly negative at all in all frames. The data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.
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.
佐甲 博之; 原田 寛之; 坂口 貴男*; 中條 達也*; 江角 晋一*; 郡司 卓*; 長谷川 勝一; Hwang, S.; 市川 裕大; 今井 憲一; et al.
Nuclear Physics A, 956, p.850 - 853, 2016/12
We are designing a large acceptance heavy-ion spectrometer at J-PARC based on a Toroidal magnet to measure hadrons, lepton pairs, and event-by-event fluctuations. We are also designing a closed geometry spectrometer to measure hypernuclei to study weak decays and magnetic moments. In this presentation, the preliminary version of the designed acceleration scheme, as well as the spectrometers and their expected performance and physics results are presented.
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.*; 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328名*
Physical Review D, 94(11), p.112008_1 - 112008_10, 2016/12
We report the double-helicity asymmetry, , in inclusive production at forward rapidity as a function of transverse momentum and rapidity . The data analyzed were taken during GeV longitudinally polarized collisions at the Relativistic Heavy Ion Collider in the 2013 run using the PHENIX detector. At this collision energy, particles are predominantly produced through gluon-gluon scatterings, thus is sensitive to the gluon polarization inside the proton. We measured by detecting the decay daughter muon pairs within the PHENIX muon spectrometers in the rapidity range . In this kinematic range, we measured the to be . The can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken : one at moderate range where recent data of jet and double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-x region Thus our new results could be used to further constrain the gluon polarization for .
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.