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論文

Observation of a Be double-Lambda hypernucleus in the J-PARC E07 experiment

江川 弘行; 足利 沙希子; 長谷川 勝一; 橋本 直; 早川 修平; 細見 健二; 市川 裕大; 今井 憲一; 金原 慎二*; 七村 拓野; et al.

Progress of Theoretical and Experimental Physics (Internet), 2019(2), p.021D02_1 - 021D02_11, 2019/02

A double-$$Lambda$$ hypernucleus, $${}_{LambdaLambda}mathrm{Be}$$, was observed by the J-PARC E07 collaborationin nuclear emulsions tagged by the $$(K^{-},K^{+})$$ reaction. This event was interpreted as a production and decay of $$ {}_{LambdaLambda}^{;10}mathrm{Be}$$,$${}_{LambdaLambda}^{;11}mathrm{Be}$$, or $${}_{LambdaLambda}^{;12}mathrm{Be}^{*}$$ via $$Xi^{-}$$ capture in $${}^{16}mathrm{O}$$.By assuming the capture in the atomic 3D state, the binding energy of two $$Lambda$$ hyperons$$,$$($$B_{LambdaLambda}$$)of these double-$$Lambda$$ hypernuclei are obtained to be$$15.05 pm 0.11,mathrm{MeV}$$, $$19.07 pm 0.11,mathrm{MeV}$$, and $$13.68 pm 0.11,mathrm{MeV}$$, respectively. Based on the kinematic fitting, $${}_{LambdaLambda}^{;11}mathrm{Be}$$ is the most likely explanation for the observed event.

論文

Low-momentum direct-photon measurement in Cu + Cu collisions at $$sqrt{s_{_{NN}}}=200$$ GeV

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

 パーセンタイル:100(Physics, Nuclear)

We have measured direct photons for $$p_T< 5~$$GeV/$$c$$ in minimum bias and 0% - 40% most central events at midrapidity for Cu$$+$$Cu collisions at $$sqrt{s_{_{NN}}}=200$$ GeV. The $$e^{+}e^{-}$$ contribution from quasi-real direct virtual photons has been determined as an excess over the known hadronic contributions in the $$e^{+}e^{-}$$ mass distribution. A clear enhancement of photons over the binary scaled $$p$$$$+$$$$p$$ fit is observed for $$p_T < 4$$ GeV/$$c$$ in Cu$$+$$Cu data. The $$p_T$$ spectra are consistent with the Au$$+$$Au data covering a similar number of participants. The inverse slopes of the exponential fits to the excess after subtraction of the $$p$$$$+$$$$p$$ baseline are 285$$pm$$53(stat)$$pm$$57(syst)~MeV/$$c$$ and 333$$pm$$72(stat)$$pm$$45(syst)~MeV/$$c$$ for minimum bias and 0% - 40% most central events, respectively. The rapidity density, $$dN/dy$$, of photons demonstrates the same power law as a function of $$dN_{rm ch}/deta$$ observed in Au$$+$$Au at the same collision energy.

論文

Production of $$pi^0$$ and $$eta$$ mesons in Cu+Au collisions at $$sqrt{s_{_{NN}}}$$=200 GeV

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:1 パーセンタイル:49.68(Physics, Nuclear)

Production of $$pi^0$$ and $$eta$$ mesons has been measured at midrapidity in Cu$$+$$Au collisions at $$sqrt{s_{_{NN}}}$$=200 GeV. Measurements were performed in $$pi^0(eta)rightarrowgammagamma$$ decay channel in the 1(2)-20 GeV/$$c$$ transverse momentum range. A strong suppression is observed for $$pi^0$$ and $$eta$$ meson production at high transverse momentum in central Cu$$+$$Au collisions relative to the $$p$$$$+$$$$p$$ results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au$$+$$Au with comparable nuclear overlap. The $$eta/pi^0$$ ratio measured as a function of transverse momentum is consistent with $$m_T$$-scaling parameterization down to $$p_T=$$2 GeV/$$c$$, its asymptotic value is constant and consistent with Au$$+$$Au and $$p$$$$+$$$$p$$ 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 $$e^+e^-$$ collisions in a range of collision energies $$sqrt{s_{_{NN}}}=$$ 3-1800 GeV. This suggests that the quark-gluon-plasma medium produced in Cu$$+$$Cu collisions either does not affect the jet fragmentation into light mesons or it affects the $$pi^0$$ and $$eta$$ the same way.

論文

Measurement of $$phi$$-meson production at forward rapidity in $$p+p$$ collisions at $$sqrt{s}=510$$ GeV and its energy dependence from $$sqrt{s}=200$$ GeV to 7 TeV

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

 パーセンタイル:100(Astronomy & Astrophysics)

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of $$phi$$(1020) meson production at forward rapidity in $$p$$$$+$$$$p$$ collisions at $$sqrt{s}=$$510 GeV via the dimuon decay channel. The integrated cross section in the rapidity and $$p_T$$ ranges $$1.2 < |y| < 2.2$$ and $$2 < p_T < 7$$ GeV/$$c$$ is $$sigma_phi=2.79 pm 0.20,{rm (stat)} pm 0.17,{rm (syst)} pm 0.34, {rm (norm)} times 10^{-2}$$~mb. The energy dependence of $$sigma_phi$$ ($$1.2 < |y|<2.2$$; $$2<p_T<5$$ GeV/$$c$$) is studied using the PHENIX measurements at $$sqrt{s}=$$200 and 510 GeV and the Large-Hadron-Collider measurements at $$sqrt{s}=$$2.76 and 7 TeV. The experimental results are compared to various event generator predictions (pythia6, pythia8, phojet, ampt, epos3, and epos-lhc).

論文

Pseudorapidity dependence of particle production and elliptic flow in asymmetric nuclear collisions of $$p$$+Al, $$p$$+Au, $$d$$+Au, and $$^{3}$$He+Au at $$sqrt{s_{_{NN}}}$$ = 200 GeV

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:3 パーセンタイル:29.91(Physics, Multidisciplinary)

Asymmetric nuclear collisions of $$p$$+Al, $$p$$+Au, $$d$$+Au, and $$^{3}$$He+Au at $$sqrt{s_{_{NN}}}$$ = 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 $$dN_{rm ch}/deta$$ 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 $$v_{2}$$ over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.

論文

Nonperturbative transverse-momentum-dependent effects in dihadron and direct photon-hadron angular correlations in $$p+p$$ collisions at $$sqrt{s}=200$$ GeV

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, 98(7), p.072004_1 - 072004_13, 2018/10

 被引用回数:1 パーセンタイル:64.74(Astronomy & Astrophysics)

Dihadron and isolated direct photon-hadron angular correlations are measured in $$p$$$$+$$$$p$$ collisions at $$sqrt{s}=200$$ GeV. The correlations are sensitive to nonperturbative initial-state and final-state transverse momentum $$k_T$$ and $$j_T$$ in the azimuthal nearly back-to-back region $$Deltaphisimpi$$. In this region, transverse-momentum-dependent evolution can be studied when several different hard scales are measured. To have sensitivity to small transverse momentum scales, nonperturbative momentum widths of $$p_{rm out}$$, the out-of-plane transverse momentum component perpendicular to the trigger particle, are measured. These widths are used to investigate possible effects from transverse-momentum-dependent factorization breaking. When accounting for the longitudinal momentum fraction of the away-side hadron with respect to the near-side trigger particle, the widths are found to increase with the hard scale; this is qualitatively similar to the observed behavior in Drell-Yan and semi-inclusive deep-inelastic scattering interactions. The momentum widths are also studied as a function of center-of-mass energy by comparing to previous measurements at $$sqrt{s}=510$$ GeV. The nonperturbative jet widths also appear to increase with $$sqrt{s}$$ at a similar $$x_T$$, which is qualitatively consistent to similar measurements in Drell-Yan interactions.

論文

Cross section and longitudinal single-spin asymmetry $$A_L$$ for forward $$W^{pm}rightarrowmu^{pm}nu$$ production in polarized $$p$$$$+$$$$p$$ collisions at $$sqrt{s}=510$$ GeV

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 $$W^{pm}rightarrowmu^{pm}nu$$ production in longitudinally polarized $$p$$$$+$$$$p$$ collisions at $$sqrt{s}=510$$ 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 $$W$$ bosons provides a natural flavor separation of the participating partons.

論文

Measurement of emission angle anisotropy via long-range angular correlations with high-$$p_T$$ hadrons in $$d$$$$+$$Au and $$p$$$$+$$$$p$$ collisions at $$sqrt{s_{_{NN}}}=200$$ GeV

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

 パーセンタイル:100(Physics, Nuclear)

We present measurements of two-particle angular correlations between high-transverse-momentum ($$2<p_T<11$$ GeV/$$c$$) $$pi^0$$ observed at midrapidity ($$|eta|<0.35$$) and particles produced either at forward ($$3.1<eta<3.9$$) or backward ($$-3.7<eta<-3.1$$) rapidity in $$d$$$$+$$Au and $$p$$$$+$$$$p$$ collisions at $$sqrt{s_{_{NN}}}=200$$ 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 $$p_T{approx}6$$ GeV/$$c$$ 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 $$d$$-going direction as well as in $$p$$$$+$$$$p$$ 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.

論文

Single-spin asymmetry of $$J/psi$$ production in $$p$$$$+$$$$p$$, $$p$$$$+$$Al, and $$p$$$$+$$Au collisions with transversely polarized proton beams at $$sqrt{s_{_{NN}}}=200$$ GeV

Aidala, C.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他286名*

Physical Review D, 98(1), p.012006_1 - 012006_11, 2018/07

 被引用回数:2 パーセンタイル:44.38(Astronomy & Astrophysics)

We report the transverse single-spin asymmetries of $$J/psi$$ production at forward and backward rapidity, $$1.2<|y|<2.2$$, as a function of $$J/psi$$ transverse momentum ($$p_T$$) and Feynman-$$x$$ ($$x_F$$). The data analyzed were recorded by the PHENIX experiment at the Relativistic Heavy Ion Collider in 2015 from $$p$$$$+$$$$p$$, $$p$$$$+$$Al, and $$p$$$$+$$Au collisions with transversely polarized proton beams at $$sqrt{s_{_{NN}}}=200$$ GeV. At this collision energy, single-spin asymmetries for heavy-flavor particle production of $$p$$$$+$$$$p$$ collisions provide access to the spin-dependent gluon distribution and higher-twist correlation functions inside the nucleon, such as the gluon Qiu-Sterman and trigluon correlation functions. Proton + nucleus collisions offer an excellent opportunity to study nuclear effects on the correlation functions. The data indicate negative asymmetries at the two-standard-deviation level in the $$p$$$$+$$Au data for $$p_T<2$$ GeV/$$c$$ at both forward and backward rapidity, while in $$p$$$$+$$$$p$$ and $$p$$$$+$$Al collisions the asymmetries are consistent with zero within the range of experimental uncertainties.

論文

Measurements of mass-dependent azimuthal anisotropy in central $$p$$ + Au, $$d$$ + Au, and $$^3$$He + Au collisions at $$sqrt{s_{_{NN}}}$$ = 200 GeV

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:4 パーセンタイル:12.26(Physics, Nuclear)

We present measurements of the transverse-momentum dependence of elliptic flow $$v_2$$ for identified pions and (anti)protons at midrapidity ($$|eta|<0.35$$), in 0% - 5% central $$p$$ + Au and $$^3$$He + Au collisions at $$sqrt{s_{_{NN}}}$$ = 200 GeV. When taken together with previously published measurements in $$d$$ + Au collisions at $$sqrt{s_{_{NN}}}$$ = 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 $$v_2(p_{T})$$ in $$d$$ + Au and $$^3$$He + Au collisions, just as in large nucleus-nucleus ($$A$$ + $$A$$) collisions, and a smaller splitting in $$p$$ + Au collisions. Both hydrodynamic and transport model calculations successfully describe the data at low $$p_T$$ ($$< 1.5$$ GeV/$$c$$), but fail to describe various features at higher $$p_T$$. In all systems, the $$v_2$$ values follow an approximate quark-number scaling as a function of the hadron transverse kinetic energy per constituent quark($$KE_T/n_q$$), which was also seen previously in $$A$$ + $$A$$ collisions.

論文

L$'{e}$vy-stable two-pion Bose-Einstein correlations in $$sqrt{s_{NN}}=200$$ GeV Au$$+$$Au 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:3 パーセンタイル:18(Physics, Nuclear)

We present a detailed measurement of charged two-pion correlation functions in 0%-30% centrality $$sqrt{s_{_{NN}}}=200$$ GeV Au$$+$$Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from L$'e$vy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter $$lambda$$, the L$'e$vy index of stability $$alpha$$ and the L$'e$vy length scale parameter $$R$$ as a function of average transverse mass of the pair $$m_T$$. 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 L$'e$vy-stable source functions. The $$lambda(m_T)$$ measurements indicate a decrease of the strength of the correlations at low $$m_T$$. The L$'e$vy length scale parameter $$R(m_T)$$ decreases with increasing $$m_T$$, following a hydrodynamically predicted type of scaling behavior. The values of the L$'e$vy index of stability $$alpha$$ are found to be significantly lower than the Gaussian case of $$alpha=2$$, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.

論文

First determination of the level structure of an $$sd$$-shell hypernucleus, $$^{19}_{Lambda}$$F

Yang, S. B.*; 江川 弘行; 長谷川 勝一; 早川 修平; 細見 健二; 市川 裕大; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; et al.

Physical Review Letters, 120, p.132505_1 - 132505_5, 2018/03

 被引用回数:1 パーセンタイル:49.95(Physics, Multidisciplinary)

We report on the first observation of $$gamma$$ rays emitted from an $$sd$$-shell hypernucleus, $$^{19}_{Lambda}$$F. The energy spacing between the ground state doublet, $$1/2^+$$ and $$3/2^+$$ states, of $$^{19}_{Lambda}$$F is determined to be $$315.5pm0.4({rm stat.})^{+0.6}_{-0.5}({rm syst.})$$ keV by measuring the $$gamma$$-ray energy of the $$M1(3/2^+ to 1/2^+)$$ transition. In addition, three $$gamma$$-ray peaks are observed and assigned as $$E2(5/2^+ to 1/2^+)$$, $$E1(1/2^- to 1/2^+)$$, and $$E1(1/2^- to 3/2^+)$$ transitions. The excitation energies of the $$5/2^+$$ and $$1/2^-$$ states are determined to be $$895.2pm0.3({rm stat.})pm0.5({rm syst.})$$ keV and $$1265.6pm1.2({rm stat.})^{+0.5}_{-0.7}({rm syst.})$$ keV, respectively. It is found that the ground state doublet spacing is well described by theoretical models based on existing $$s$$- and $$p$$-shell hypernuclear data.

論文

Heavy ion acceleration at J-PARC

佐藤 進; J-PARC Heavy Ion Collaboration*

EPJ Web of Conferences (Internet), 171, p.21002_1 - 21002_4, 2018/02

 パーセンタイル:100

J-PARCは現在、大強度陽子加速器を用いた研究が精力的に進められているが、近年、国内だけでなく国際的なコミュニティーから、重イオンの加速を併設する計画研究(J-PARC-HI)が活発になっている。本発表では、このJ-PARC-HIにおける物理研究テーマを報告するととともに、J-PARCの現状についても併せて報告する。

論文

Measurements of multiparticle correlations in $$d$$+Au Collisions at 200, 62.4, 39, and 19.6 GeV and $$p$$+Au Collisions at 200 GeV and implications for collective behavior

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:8 パーセンタイル:5.39(Physics, Multidisciplinary)

Recently, multiparticle-correlation measurements of relativistic $$p/d/^3$$He$$+$$Au, $$p$$$$+$$Pb, and even $$p$$$$+$$$$p$$ collisions have shown surprising collective signatures. Here we present beam-energy-scan measurements of 2-, 4-, and 6-particle angular correlations in $$d$$$$+$$Au collisions at $$sqrt{s_{_{NN}}}$$=200, 62.4, 39, and 19.6 GeV. We also present measurements of 2- and 4-particle angular correlations in $$p$$$$+$$Au collisions at $$sqrt{s_{_{NN}}}$$=200 GeV. We find the 4-particle cumulant to be real-valued for $$d$$$$+$$Au collisions at all four energies. We also find that the 4-particle cumulant in $$p$$$$+$$Au has the opposite sign as that in $$d$$$$+$$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 $$d$$$$+$$Au collisions at 200 GeV, which indicates that nonflow effects are subdominant and provides strong evidence of collectivity.

論文

Nuclear dependence of the transverse-single-spin asymmetry for forward neutron production in polarized $$p$$$$+$$$$A$$ collisions at $$sqrt{s_{_{NN}}}=200$$ GeV

Aidala, C.*; 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 Letters, 120, p.022001_1 - 022001_9, 2018/01

 被引用回数:2 パーセンタイル:29.91(Physics, Multidisciplinary)

During 2015 the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized $$p+p$$ collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in $$p+p$$ collisions predicts only a moderate atomic-mass-number ($$A$$) dependence. In contrast, the asymmetries observed at RHIC in $$p+A$$ collisions showed a surprisingly strong $$A$$ dependence in inclusive forward neutron production. The observed asymmetry in $$p$$+Al collisions is much smaller, while the asymmetry in $$p$$ + Au collisions is a factor of three larger in absolute value and of opposite sign. The interplay of different neutron production mechanisms is discussed as a possible explanation of the observed $$A$$ dependence.

論文

$$B$$-meson production at forward and backward rapidity in $$p+p$$ and Cu + Au collisions at $$sqrt{s_{_{NN}}}$$ = 200 GeV

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:1 パーセンタイル:72.32(Physics, Nuclear)

The fraction of $$J/psi$$ mesons which come from B-meson decay, $$textrm{F}_{B{rightarrow}J/psi}$$, is measured for J/$$psi$$ rapidity $$1.2<|y|< 2.2$$ and $$p_T>0$$ in $$p$$+$$p$$ and Cu+Au collisions at $$sqrt{s_{_{NN}}}$$=200 GeV with the PHENIX detector. The extracted fraction is $$textrm{F}_{B{rightarrow}J/psi}$$ = 0.025 $$pm$$ 0.006(stat) $$pm$$ 0.010(syst) for $$p$$+$$p$$ collisions. For Cu+Au collisions, $$textrm{F}_{B{rightarrow}J/psi}$$ is 0.094 $$pm$$ 0.028(stat) $$pm$$ 0.037(syst) in the Au-going direction ($$-2.2<y<-1.2$$) and 0.089 $$pm$$ 0.026(stat) $$pm$$ 0.040(syst) in the Cu-going direction ($$1.2<y<2.2$$). The nuclear modification factor, $$R_{rm CuAu}$$, of B mesons in Cu+Au collisions is consistent with binary scaling of measured yields in $$p$$+$$p$$ at both forward and backward rapidity.

論文

Measurements of azimuthal anisotropy and charged-particle multiplicity in $$d$$ + Au collisions at $$sqrt{s_{_{NN}}}$$ = 200, 62.4, 39, and 19.6 GeV

Aidala, C.*; 長谷川 勝一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他246名*

Physical Review C, 96(6), p.064905_1 - 064905_21, 2017/12

 被引用回数:12 パーセンタイル:6.79(Physics, Nuclear)

We present measurements of the elliptic flow, $$v_2$$, as a function of transverse momentum ($$p_T$$), pseudorapidity ($$eta$$), and centrality in $$d$$$$+$$Au collisions at $$sqrt{s_{_{NN}}}=$$200, 62.4, 39, and 19.6 GeV. The beam-energy scan of $$d$$$$+$$Au collisions provides a testing ground for the onset of flow signatures in small collision systems. We measure a nonzero $$v_2$$ signal at all four collision energies, which, at midrapidity and low $$p_T$$, is consistent with predictions from viscous hydrodynamic models. Comparisons with calculations from parton transport models (based on the ${sc ampt}$ Monte Carlo generator) show good agreement with the data at midrapidity to forward ($$d$$-going) rapidities and low $$p_T$$. At backward (Au-going) rapidities and $$p_T > 1.5$$ GeV/$$c$$, the data diverges from ${sc ampt}$ calculations of $$v_2$$ relative to the initial geometry, indicating the possible dominance of nongeometry related correlations, referred to as nonflow. We also present measurements of the charged-particle multiplicity ($$dN_{rm ch}/deta$$) as a function of $$eta$$ in central $$d$$$$+$$Au collisions at the same energies. We find that in $$d$$$$+$$Au collisions at $$sqrt{s_{_{NN}}}=$$200 GeV the $$v_2$$ scales with $$dN_{rm ch}/deta$$ over all $$eta$$ in the PHENIX acceptance. At $$sqrt{s_{_{NN}}}=$$62.4, and 39 GeV, $$v_2$$ scales with $$dN_{rm ch}/deta$$ at midrapidity and forward rapidity, but falls off at backward rapidity. This departure from the $$dN_{rm ch}/deta$$ scaling may be a further indication of nonflow effects dominating at backward rapidity.

論文

Spectroscopy of nuclei with multi-strangeness by using new S-2S spectrometer at J-PARC

後神 利志*; 江川 弘行; 長谷川 勝一; 早川 修平; 細見 健二; 今井 憲一; 市川 裕大; 七村 拓野; 成木 恵; 佐甲 博之; et al.

JPS Conference Proceedings (Internet), 18, p.011031_1 - 011031_6, 2017/11

The missing mass spectroscopy of $$Xi^-$$ hypernuclei is planned at the Japan Proton Accelerator Research Complex (J-PARC) by using the $$(K^-,K^+)$$ reaction. We are constructing a new magnetic spectrometer, S-2S, which has a better momentum resolution [$$Delta p/p = 5 times 10^{-4}$$ (FHWM)] than that of an existing spectrometer (SKS) at J-PARC. S-2S would give us an opportunity to confirm the existence of $$Xi^-$$ hypernuclei as a peak structure owing to both the high momentum resolution and its reasonably large solid angle. Brief descriptions of our experiment and of its preparation status are presentedin this article.

論文

Measurements of $$e^+e^-$$ pairs from open heavy flavor in $$p+p$$ and $$d+A$$ collisions at $$sqrt{s_{NN}}$$ = 200 GeV

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

AA2017-0466.pdf:2.14MB

 被引用回数:9 パーセンタイル:11.96(Physics, Nuclear)

We report a measurement of $$e^+e^-$$ pairs from semileptonic heavy-flavor decays in $$p+p$$ collisions at $$sqrt{s_{NN}}$$ = 200 GeV. The $$e^+e^-$$ pair yield from $$bbar{b}$$ and $$cbar{c}$$ is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and $$p_T$$. We used three different event generators, ${sc pythia}$, ${sc mc@nlo}$, and ${sc powheg}$, to simulate the $$e^+e^-$$ spectra from $$bbar{b}$$ and $$cbar{c}$$ production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to $$4pi$$, significant differences are observed for the total cross section. These difference are less pronounced for $$bbar{b}$$ than for $$cbar{c}$$. The same model dependence was observed in already published $$d+A$$ data. The $$p+p$$ data are also directly compared with $$d+A$$ data in mass and $$p_T$$, and within the statistical accuracy no nuclear modification is seen.

論文

$$gamma$$-ray spectroscopy of hypernuclei; Recent results and prospect at J-PARC

田村 裕和*; 江川 弘行; 長谷川 勝一; 早川 修平; 細見 健二; Hwang, S.; 市川 裕大; 今井 憲一; 佐甲 博之; 佐藤 進; et al.

JPS Conference Proceedings (Internet), 17, p.011004_1 - 011004_11, 2017/07

The present status and future prospects of precision $$gamma$$-ray spectroscopy of $$Lambda$$ hypernuclei are described. A new experiment (J-PARC E13) has been performed at the J-PARC K1.8 line employing a newly-developed germanium (Ge) detector array, Hyperball-J, via the $$(K^-,pi^-)$$ reaction on $$^4$$He and $$^{19}$$F targets. This is the first study of $$s$$-shell and $$sd$$-shell $$Lambda$$ hypernuclei with Ge detectors. The $$^4$$He target spectrum exhibited a $$gamma$$-ray peak of $$^4_{Lambda}{rm He}(1^+to 0^+)$$ at $$1.406 pm 0.002 pm 0.002$$ MeV. Compared with the energy ($$1.09 pm 0.02$$ MeV) of the corresponding transition for the mirror hypernucleus, $$^4_{Lambda}{rm H}(1^+to 0^+)$$, the present result clearly indicates a large charge symmetry breaking (CSB) effect. This decisive data for CSB allows a stringent test of baryon-baryon interaction models. As for the $$^{19}$$F target run, a preliminary spectrum shows several $$gamma$$-ray peaks assigned to $$^{19}_{Lambda}{rm F}$$ transitions. Future plans of $$gamma$$-ray spectroscopy are also discussed.

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