Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
岩崎 幸生*; 慈道 大介*; 岡 眞; 鈴木 渓
Physics Letters B, 820, p.136498_1 - 136498_6, 2021/09
被引用回数:2 パーセンタイル:18.91(Astronomy & Astrophysics)本論文では、時間依存する空間一様磁場中でのS波チャーモニウムの時間発展を数値的に計算し、各固有状態が磁場の減衰後にどれだけ生き残るかを示す指標(残存確率)を見積もる。このような研究は、RHICやLHCなどで行われている相対論的重イオン衝突実験において瞬間的に生成される磁場の測定(特に、磁場の大きさや磁場の寿命の測定)に役立つことが期待される。本解析では、磁場中で起こる異なるスピン固有状態の混合効果や高軌道励起状態への遷移効果が含まれており、これらの効果は最終的な残存確率に影響を及ぼす。結果として、磁場の寿命が極端に短い場合でさえも残存確率の有意な変化が見られることや、残存確率が初期状態のスピン配位に依存することが判明した。このような残存確率は、スピンパートナー同士(スピン1重項とスピン3重項)の和をとることにより初期配位に依存しない量となり、この量はの関数(は磁場の寿命、は磁場の最大値に対応するパラメータ)として表されることを示す。
岩崎 幸生*; 岡 眞; 鈴木 渓
European Physical Journal A, 57(7), p.222_1 - 222_14, 2021/07
被引用回数:17 パーセンタイル:70.63(Physics, Nuclear)クォーコニウムとは、チャームクォークやボトムクォークのような「重い」クォークとその反クォークから構成される中間子であり、水素原子やポジトロニウムなどの原子物理との類似点を持ちつつも、量子色力学(QCD)由来の性質も併せ持つ興味深い系である。ハドロン物理における典型的なスケールに匹敵する強磁場は、相対論的重イオン衝突実験や強磁場中性子星(マグネター)と関連して注目を集めている。本論文は、強磁場中のクォーコニウムの性質についてまとめたレビュー論文である。磁場中のクォーコニウムにおける特徴的な物理現象として、(1)異なるスピン固有状態間の混合効果、(2)クォーク自由度に対するランダウ準位とハドロン波動関数の変形現象、(3)クォーク・反クォーク間ポテンシャルの修正、(4)運動的シュタルク効果について解説を行う。また、磁場中のクォーコニウムを記述するための理論手法のまとめとして、(1)構成子クォーク模型、(2)有効ラグランジアンによる手法、(3)QCD和則、(4)ホログラフィックQCDについて解説する。さらに、有限温度,有限密度,有限渦度などの磁場以外の外場効果による影響についても述べる。付録において磁場中のクォーコニウムの典型的な質量スペクトルや波動関数を例示する。
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
被引用回数:5 パーセンタイル:52.72(Physics, Nuclear)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.
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
被引用回数:30 パーセンタイル:86.91(Physics, Multidisciplinary)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
被引用回数:15 パーセンタイル:83.07(Physics, Nuclear)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293名*
Physical Review C, 99(4), p.044912_1 - 044912_10, 2019/04
被引用回数:5 パーセンタイル:47.88(Physics, Nuclear)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312名*
Nature Physics, 15(3), p.214 - 220, 2019/03
被引用回数:149 パーセンタイル:99.03(Physics, Multidisciplinary)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
被引用回数:11 パーセンタイル:74.44(Physics, Nuclear)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
被引用回数:14 パーセンタイル:75.94(Physics, Nuclear)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
被引用回数:11 パーセンタイル:68.32(Physics, Nuclear)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
被引用回数:34 パーセンタイル:86.03(Physics, Multidisciplinary)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
被引用回数:7 パーセンタイル:53.6(Physics, Nuclear)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
被引用回数:22 パーセンタイル:86.47(Physics, Nuclear)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
被引用回数:32 パーセンタイル:92.26(Physics, Nuclear)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
被引用回数:42 パーセンタイル:89.79(Physics, Multidisciplinary)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
被引用回数:3 パーセンタイル:27.61(Physics, Nuclear)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
被引用回数:11 パーセンタイル:65.8(Physics, Nuclear)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
被引用回数:11 パーセンタイル:49.91(Astronomy & Astrophysics)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
被引用回数:74 パーセンタイル:97.96(Physics, Nuclear)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
被引用回数:24 パーセンタイル:84.18(Physics, Nuclear)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 .