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.*; 今井 憲一; 永宮 正治; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他506名*
Physical Review C, 93(1), p.011901_1 - 011901_8, 2016/01
We report the measurement of cumulants (, ) of the net-charge distributions measured within pseudorapidity () in Au + Au collisions at = 7.7-200 GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider. The ratios of cumulants (e.g., , ) of the net-charge distributions, which can be related to volume independent susceptibility ratios, are studied as a function of centrality and energy. These quantities are important to understand the quantum-chromodynamics phase diagram and possible existence of a critical end point. The measured values are very well described by expectation from negative binomial distributions. We do not observe any nonmonotonic behavior in the ratios of the cumulants as a function of collision energy. The measured values of and can be directly compared to lattice quantum-chromodynamics calculations and thus allow extraction of both the chemical freeze-out temperature and the baryon chemical potential at each center-of-mass energy. The extracted baryon chemical potentials are in excellent agreement with a thermal-statistical analysis model.
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477名*
Physical Review C, 92(4), p.044909_1 - 044909_14, 2015/10
The PHENIX Collaboration has measured meson production in + Au collisions at = 200 GeV using the dimuon and dielectron decay channels. The meson is measured in the forward (backward) -going (Au-going) direction, in the transverse-momentum () range from 1-7 GeV/ and at midrapidity in the range below 7 GeV/. The meson invariant yields and nuclear-modification factors as a function of , rapidity, and centrality are reported. An enhancement of meson production is observed in the Au-going direction, while suppression is seen in the -going direction, and no modification is observed at midrapidity relative to the yield in collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects.
Adare, A.*; 今井 憲一; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他420名*
Physical Review C, 92(3), p.034913_1 - 034913_20, 2015/09
We have studied the dependence of azimuthal anisotropy for inclusive and identified charged hadrons in Au + Au and Cu + Cu collisions on collision energy, species, and centrality. The values of as a function of transverse momentum and centrality in Au+Au collisions at = 200 and 62.4 GeV are the same within uncertainties. However, in Cu + Cu collisions we observe a decrease in values as the collision energy is reduced from 200 to 62.4 GeV. The decrease is larger in the more peripheral collisions. By examining both Au + Au and Cu + Cu collisions we find that depends both on eccentricity and the number of participants, . We observe that divided by eccentricity () monotonically increases with and scales as . The Cu + Cu data at 62.4 GeV falls below the other scaled data. For identified hadrons, divided by the number of constituent quarks is independent of hadron species as a function of transverse kinetic energy between GeV. Combining all of the above scaling and normalizations, we observe a near-universal scaling, with the exception of the Cu + Cu data at 62.4 GeV, of vs for all measured particles.
Adare, A.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他493名*
Physical Review C, 92(3), p.034914_1 - 034914_21, 2015/09
We present a systematic study of charged-pion and kaon interferometry in Au + Au collisions at = 200 GeV. The kaon mean source radii are found to be larger than pion radii in the outward and longitudinal directions for the same transverse mass; this difference increases for more central collisions. The azimuthal angle dependence of the radii was measured with respect to the second-order event plane and similar oscillations of the source radii were found for pions and kaons. Hydrodynamic models qualitatively describe the similar oscillations of the mean source radii for pions and kaons, but they do not fully describe the transverse-mass dependence of the oscillations.
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 Letters, 115(14), p.142301_1 - 142301_9, 2015/09
We present the first measurement of elliptic () and triangular () flow in high-multiplicity He + Au collisions at = 200 GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in He + Au and in collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the He + Au system. The collective behavior is quantified in terms of elliptic and triangular anisotropy coefficients measured with respect to their corresponding event planes. The values are comparable to those previously measured in + Au collisions at the same nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three He nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.
Adare, A.*; 今井 憲一; 谷田 聖; PHENIX Collaboration*; 他504名*
Physical Review C, 91(2), p.024913_1 - 024913_16, 2015/02
Measurements of bottomonium production in heavy-ion and collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three states, , was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au+Au and collisions at GeV. The differential cross section at midrapidity was found to be pb in collisions. The nuclear modification factor in the 30% most central Au+Au collisions indicates a suppression of the total state yield relative to the extrapolation from collision data. The suppression is consistent with measurements made by STAR at RHIC and at higher energies by the CMS experiment at the Large Hadron Collider.
秋村 友香; 丸山 敏毅; 吉永 尚孝*; 千葉 敏
European Physical Journal A, 25(3), p.405 - 411, 2005/09
丸山 敏毅; 千葉 敏
JAERI-Conf 2003-009, 233 Pages, 2003/08
no journal, ,
通常の近藤効果は金属中に局在する不純物によって引き起こされ、系の電気的/熱的/輸送的性質に対して大きな影響を及ぼす。一方で、高密度のクォーク物質においては、比較的重い不純物クォークと軽いクォークとのカラー交換相互作用によって同様の効果が起こることが期待されている(QCD近藤効果)。この講演では、Refs.~[1,2]において予言された、ライトクォークとヘビークォークから成る凝縮によって特徴づけられる新しい相についてレビューを行う。特に、この相における励起状態として現れる様々なエキシトンモードについて議論を行う~。これらのモードは高密度クォーク物質における輸送的性質に寄与することが期待される。 S. Yasui, K. Suzuki, and K. Itakura, Nucl. Phys. A983 (2019) 90.  S. Yasui, K. Suzuki, and K. Itakura, Phys. Rev. D96 (2017) 014016.  D. Suenaga, K. Suzuki, and S. Yasui, arXiv:1909.07573.