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論文

Production of $$bbar{b}$$ at forward rapidity in $$p+p$$ collisions at $$sqrt{s}=510$$ GeV

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344名*

Physical Review D, 102(9), p.092002_1 - 092002_14, 2020/11

 被引用回数:0 パーセンタイル:0.01(Astronomy & Astrophysics)

The cross section of bottom quark-antiquark ($$bbar{b}$$) production in $$p+p$$ collisions at $$sqrt{s}=510$$ GeV is measured with the PHENIX detector at the Relativistic Heavy Ion Collider. The results are based on the yield of high mass, like-sign muon pairs measured within the PHENIX muon arm acceptance ($$1.2 < |y| < 2.2$$). The $$bbar{b}$$ signal is extracted from like-sign dimuons by utilizing the unique properties of neutral $$B$$ meson oscillation. We report a differential cross section of $$dsigma_{bbar{b} rightarrow mu^pmmu^pm}/dy = 0.16 pm 0.01~(mbox{stat}) pm 0.02~(mbox{syst}) pm 0.02~(mbox{global})$$ nb for like-sign muons in the rapidity and $$p_T$$ ranges $$1.2 < |y| < 2.2$$ and $$p_T > 1$$ GeV/$$c$$, and dimuon mass of 5 - 10 GeV/$$c^2$$. The extrapolated total cross section at this energy for $$bbar{b}$$ production is $$13.1 pm 0.6~(mbox{stat}) pm 1.5~(mbox{syst}) pm 2.7~(mbox{global})~mu$$b. The total cross section is compared to a perturbative quantum chromodynamics calculation and is consistent within uncertainties. The azimuthal opening angle between muon pairs from $$bbar{b}$$ decays and their $$p_T$$ distributions are compared to distributions generated using ${sc ps pythia 6}$, which includes next-to-leading order processes. The azimuthal correlations and pair $$p_T$$ distribution are not very well described by ${sc pythia}$ calculations, but are still consistent within uncertainties. Flavor creation and flavor excitation subprocesses are favored over gluon splitting.

論文

Polarization and cross section of midrapidity $$J/psi$$ production in $$p+p$$ collisions at $$sqrt{s}=510$$ GeV

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344名*

Physical Review D, 102(7), p.072008_1 - 072008_13, 2020/10

 被引用回数:0 パーセンタイル:0.01(Astronomy & Astrophysics)

The PHENIX experiment has measured the spin alignment for inclusive $$J/psi rightarrow e^{+}e^{-}$$ decays in $$p+p$$ collisions at $$sqrt{s}=510$$ GeV at midrapidity. The angular distributions have been measured in three different polarization frames, and the three decay angular coefficients have been extracted in a full two-dimensional analysis. Previously, PHENIX saw large longitudinal net polarization at forward rapidity at the same collision energy. This analysis at midrapidity, complementary to the previous PHENIX results, sees no sizable polarization in the measured transverse momentum range of $$0.0 < p_T < 10.0$$ GeV/$$c$$. The results are consistent with a previous one-dimensional analysis at midrapidity at $$sqrt{s}=200$$ GeV. The transverse-momentum-dependent cross section for midrapidity $$J/psi$$ production has additionally been measured, and after comparison to world data we find a simple logarithmic dependence of the cross section on $$sqrt{s}$$.

論文

Measurement of charged pion double spin asymmetries at midrapidity in longitudinally polarized $$p$$$$+$$$$p$$ collisions at $$sqrt{s}=510$$ GeV

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354名*

Physical Review D, 102(3), p.032001_1 - 032001_9, 2020/08

 被引用回数:1 パーセンタイル:22.99(Astronomy & Astrophysics)

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the longitudinal double spin asymmetries, $$A_{LL}$$, for charged pions at midrapidity ($$|eta| < 0.35$$) in longitudinally polarized $$p$$$$+$$$$p$$ collisions at $$sqrt{s}=510$$ GeV. These measurements are sensitive to the gluon spin contribution to the total spin of the proton in the parton momentum fraction $$x$$ range between 0.04 and 0.09. One can infer the sign of the gluon polarization from the ordering of pion asymmetries with charge alone. The asymmetries are found to be consistent with global quantum-chromodynamics fits of deep-inelastic scattering and data at $$sqrt{s}=200$$ GeV, which show a nonzero positive contribution of gluon spin to the proton spin.

論文

$$J/psi$$ and $$psi(2S)$$ production at forward rapidity in $$p$$+$$p$$ collisions at $$sqrt{s}=510$$ GeV

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

 被引用回数:2 パーセンタイル:40.85(Astronomy & Astrophysics)

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section, mean transverse momentum, mean transverse momentum squared of inclusive $$J/psi$$ and cross-section ratio of $$psi(2S)$$ to $$J/psi$$ at forward rapidity in $$pp$$ collisions at $$sqrt{s} = 510$$ GeV via the dimuon decay channel. Comparison is made to inclusive $$J/psi$$ cross sections measured at $$sqrt{s} = 200$$ 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-$$x$$ gluons in the proton at low transverse momentum ($$p_T$$) and to next-to-leading order nonrelativistic QCD calculations for the rest of the $$p_T$$ range. These calculations overestimate the data at low $$p_T$$. While consistent with the data within uncertainties above $$approx 3$$ GeV/$$c$$, the calculations are systematically below the data. The total cross section times the branching ratio is BR $$dsigma^{J/psi}_{pp}/dy (1.2 < |y| < 2.2, 0 < p_T < 10$$ GeV/$$c$$) = 54.3 $$pm$$ 0.5 (stat) $$pm$$ 5.5 (syst) nb.

論文

Beam energy and centrality dependence of direct-photon emission from ultrarelativistic heavy-ion 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:13 パーセンタイル:83.95(Physics, Multidisciplinary)

The PHENIX collaboration presents first measurements of low-momentum (0.4 $$< p_T <$$ 3 GeV/$$c$$) direct-photon yields from Au$$+$$Au collisions at $$sqrt{s_{_{NN}}}$$ = 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 Au$$+$$Au collisions at $$sqrt{s_{_{NN}}}$$ = 200. Analyzing the photon yield as a function of the experimental observable $$dN_{rm ch}/deta$$ reveals that the low-momentum ($$>$$1 GeV/$$c$$) direct-photon yield $$dN_{gamma}^{rm dir}/deta$$ is a smooth function of $$dN_{rm ch}/deta$$ and can be well described as proportional to $$(dN_{rm ch}/deta)^alpha$$ with $$alpha approx$$ 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, $$A+A$$ collision systems. At a given beam energy the scaling also holds for high $$p_T$$ ($$>$$5 GeV/$$c$$) but when results from different collision energies are compared, an additional $$sqrt{s_{_{NN}}}$$-dependent multiplicative factor is needed to describe the integrated-direct-photon yield.

論文

Measurement of two-particle correlations with respect to second- and third-order event planes in Au$$+$$Au 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451名*

Physical Review C, 99(5), p.054903_1 - 054903_29, 2019/05

AA2019-0567.pdf:3.42MB

 被引用回数:8 パーセンタイル:84.14(Physics, Nuclear)

We present measurements of azimuthal correlations of charged hadron pairs in $$sqrt{s_{_{NN}}}=200$$ GeV Au$$+$$Au collisions after subtracting an underlying event using a model that includes higher-order azimuthal anisotropy $$v_2$$, $$v_3$$, and $$v_4$$. After subtraction, the away-side ($$Deltaphisimpi)$$ of the highest transverse-momentum trigger ($$p_T > 4$$ GeV/$$c$$) correlations is suppressed compared to that of correlations measured in $$p$$$$+$$$$p$$ collisions. At the lowest associated particle $$p_T$$, the away-side shape and yield are modified. These observations are consistent with the scenario of radiative-jet energy loss. For the lowest-$$p_T$$ 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 $$Psi_n$$. The angular correlations show an asymmetry when selecting the sign of the trigger-particle azimuthal angle with respect to the $$Psi_2$$ 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 $$Psi_3$$ dependence can be resolved within experimental uncertainties.

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

 被引用回数:10 パーセンタイル:76.63(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:5 パーセンタイル:56.63(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

 被引用回数:0 パーセンタイル:0.01(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

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

 被引用回数:10 パーセンタイル:63.01(Astronomy & Astrophysics)

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

 被引用回数:5 パーセンタイル:49.58(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

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:21 パーセンタイル:92.92(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

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:11 パーセンタイル:76.57(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

Missing-mass spectroscopy with the $$^6$$Li$$(pi^-,K^+)X$$ reaction to search for $$^6_Lambda$$H

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

AA2017-0465.pdf:1.08MB

 被引用回数:11 パーセンタイル:76.57(Physics, Nuclear)

We searched for the bound state of the neutron-rich $$Lambda$$-hypernucleus $$^6_Lambda$$H, using the $$^6$$Li$$(pi^-,K^+)X$$ double charge-exchange reaction at a $$pi^-$$ beam momentum of 1.2 GeV/$$c$$ at J-PARC. A total of $$1.4 times 10^{12}$$ $$pi^-$$ was driven onto a $$^6$$Li target of 3.5 g/cm$$^2$$ thickness. No event was observed below the bound threshold, i.e., the mass of $$^4_Lambda$$H+$$2n$$, in the missing-mass spectrum of the $$^6$$Li$$(pi^-,K^+)X$$ reaction in the $$2^{circ} < theta_{pi K} <20^{circ}$$ angular range. Furthermore, no event was found up to 2.8 MeV/c$$^2$$ above the bound threshold.

論文

Cross section and transverse single-spin asymmetry of muons from open heavy-flavor decays in polarized $$p+p$$ collisions at $$sqrt{s}$$=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431名*

Physical Review D, 95(11), p.112001_1 - 112001_15, 2017/06

AA2017-0235.pdf:0.72MB

 被引用回数:12 パーセンタイル:61.01(Astronomy & Astrophysics)

The cross section and transverse single-spin asymmetries of $$mu^-$$ and $$mu^+$$ from open heavy-flavor decays in polarized $$p+p$$ collisions at $$sqrt{s}$$ = 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 $$sqrt{s}$$ = 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 ($$1.4 < |y| < 2.0$$) over the transverse momentum range of $$1.25 < p_T < 7$$ GeV/$$c$$ for the cross section and $$1.25 < p_T < 5$$ GeV/$$c$$ 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.

論文

Measurements of $$B to J/psi$$ at forward rapidity in $$p+p$$ collisions at $$sqrt{s}=510$$ 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425名*

Physical Review D, 95(9), p.092002_1 - 092002_18, 2017/05

AA2017-0101.pdf:1.49MB

 被引用回数:7 パーセンタイル:46.18(Astronomy & Astrophysics)

We report the first measurement of the fraction of $$J/psi$$ mesons coming from $$B$$-meson decay ($$F_{B to J/psi}$$) in $$p+p$$ collisions at $$sqrt{s}=510$$ 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 $$J/psi$$ due to $$B$$-meson decays from prompt $$J/psi$$. The measured value of $$F_{B to J/psi}$$ is $$8.1% pm 2.3%{(rm stat)} pm1.9% {(rm syst)}$$ for $$J/psi$$ with transverse momenta $$0 < p_T < 5$$ GeV/$$c$$ and rapidity $$1.2<|y|<2.2$$. The measured fraction $$F_{B to J/psi}$$ 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 $$bbar{b}$$ cross section per unit rapidity $$[dsigma/dy(pp to bbar{b})]$$ extracted from the obtained $$F_{B to J/psi}$$ and the PHENIX inclusive $$J/psi$$ cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean $$B$$ hadron rapidity $$y=pm 1.7$$ in 510 GeV $$p+p$$ collisions, is $$3.63_{-1.70}^{+1.92}$$ $$mu$$b. It is consistent with the fixed-order-next-to-leading-logarithm calculations.

論文

Angular decay coefficients of $$J/psi$$ mesons at forward rapidity from $$p+p$$ 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389名*

Physical Review D, 95(9), p.092003_1 - 092003_13, 2017/05

AA2017-0100.pdf:0.69MB

 被引用回数:2 パーセンタイル:17.75(Astronomy & Astrophysics)

We report the first measurement of the full angular distribution for inclusive $$J/psirightarrowmu^{+}mu^{-}$$ decays in $$p$$$$+$$$$p$$ collisions at $$sqrt{s}=510$$ GeV. The measurements are made for $$J/psi$$ transverse momentum $$2 < p_{T} < 10$$ GeV/$$c$$ and rapidity $$1.2 < y < 2.2$$ in the Helicity, Collins-Soper, and Gottfried-Jackson reference frames. In all frames the polar coefficient $$lambda_{theta}$$ is strongly negative at low $$p_{T}$$ and becomes close to zero at high $$p_{T}$$, while the azimuthal coefficient $$lambda_{phi}$$ is close to zero at low $$p_{T}$$, and becomes slightly negative at higher $$p_{T}$$. The frame-independent coefficient $$tilde{lambda}$$ is strongly negative at all $$p_{T}$$ in all frames. The data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.

論文

Nonperturbative-transverse-momentum effects and evolution in dihadron and direct photon-hadron angular correlations in $$p+p$$ 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462名*

Physical Review D, 95(7), p.072002_1 - 072002_19, 2017/04

AA2017-0102.pdf:1.1MB

 被引用回数:9 パーセンタイル:54.4(Astronomy & Astrophysics)

Dihadron and isolated direct photon-hadron angular correlations are measured in $$p+p$$ collisions at $$sqrt{s}$$ = 510 GeV. Correlations of charged hadrons of $$0.7 < p_T < 10$$ GeV/$$c$$ with $$pi^0$$ mesons of $$4 < p_T < 15$$ GeV/$$c$$ or isolated direct photons of $$7 < p_T < 15$$ GeV/$$c$$ 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 $$p_{rm out}$$ perpendicular to the axis of the trigger particle, which is the high-$$p_T$$ direct photon or $$pi^0$$. Nonperturbative evolution effects are extracted from Gaussian fits to the away-side inclusive-charged-hadron yields for different trigger-particle transverse momenta ($$p_{T}^{rm trig}$$). The Gaussian widths and root mean square of $$p_{rm out}$$ are reported as a function of the interaction hard scale $$p_{T}^{rm trig}$$ to investigate possible transverse-momentum-dependent evolution differences between the $$pi^0$$-$$h^pm$$ and direct photon-$$h^{pm}$$ correlations and factorization breaking effects. The widths are found to decrease with $$p_{T}^{rm trig}$$, 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 $$p+p$$ collisions. This behavior is in contrast to Drell-Yan and semi-inclusive deep-inelastic scattering measurements.

論文

Studies of high density baryon matter with high intensity heavy-ion beams at J-PARC

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

 被引用回数:11 パーセンタイル:71(Physics, Nuclear)

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.

論文

Azimuthally anisotropic emission of low-momentum direct photons in Au+Au 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545名*

Physical Review C, 94(6), p.064901_1 - 064901_14, 2016/12

AA2016-0473.pdf:0.66MB

 被引用回数:53 パーセンタイル:97.71(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 $$sqrt{s_{NN}}$$ = 200 GeV for various collision centralities. Combining two different analysis techniques, results were obtained in the transverse momentum range of $$0.4 < p_T < 4.0$$ GeV/$$c$$. At low $$p_T$$ the second-order coefficients, $$v_2$$, are similar to the ones observed in hadrons. Third-order coefficients, $$v_3$$, are nonzero and almost independent of centrality. These new results on $$v_2$$ and $$v_3$$, 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.

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