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Sökning: WFRF:(Ichimiya R.)

  • Resultat 1-10 av 60
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  • Adare, A., et al. (författare)
  • Inclusive double-helicity asymmetries in neutral-pion and eta-meson production in <(p) over right arrow> + <(p) over right arrow> collisions at root s=200 GeV
  • 2014
  • Ingår i: Physical Review D. - Amer. Physical Soc.. - 1550-7998. ; 90:1, s. 012007
  • Tidskriftsartikel (refereegranskat)abstract
    • Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, A(LL), for pi(0) and eta production in root s = 200 GeV polarized p + p collisions. Comparison of the pi(0) results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, Delta G, in the proton in the probed Bjorken x range. The effect of adding the new 2009 pi(0) data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit Delta G(DSSV)([0.05,0.2]) = 0.06(-0.15)(+0.11) in the range 0.05 &lt; x &lt; 0.2, with the uncertainty at Delta chi(2) = 9 when considering only statistical experimental uncertainties. Shifting the PHENIX data points by their systematic uncertainty leads to a variation of the best-fit value of Delta G(DSSV)([0.05,0.2]) between 0.02 and 0.12, demonstrating the need for full treatment of the experimental systematic uncertainties in future global analyses.
  • Adare, A., et al. (författare)
  • Charged-pion cross sections and double-helicity asymmetries in polarized p plus p collisions at root s=200 GeV
  • 2015
  • Ingår i: Physical Review D. - Amer Physical Soc. - 1550-7998. ; 91:3, s. 032001
  • Tidskriftsartikel (refereegranskat)abstract
    • We present midrapidity charged-pion invariant cross sections, the ratio of the pi(-) to pi(+) cross sections and the charge-separated double-spin asymmetries in polarized p + p collisions at root s = p + 200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The charge-separated pion asymmetries presented here sample an x range of similar to 0.03-0.16 and provide unique information on the sign of the gluon-helicity distribution.
  • Adare, A., et al. (författare)
  • Cross Section and Parity-Violating Spin Asymmetries of W-+/- Boson Production in Polarized p plus p Collisions at root s=500 Gev
  • 2011
  • Ingår i: Physical Review Letters. - Amer Physical Soc. - 0031-9007. ; 106:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Large parity-violating longitudinal single-spin asymmetries A(L)(e+) = 0.86(-0.14)(+0.30) and Ae(L)(e-) = 0.88(-0.71)(+0.12) are observed for inclusive high transverse momentum electrons and positrons in polarized p + p collisions at a center-of-mass energy of root s = 500 GeV with the PHENIX detector at RHIC. These e(+/-) come mainly from the decay of W-+/- and Z(0) bosons, and their asymmetries directly demonstrate parity violation in the couplings of the W-+/- to the light quarks. The observed electron and positron yields were used to estimate W-+/- boson production cross sections for the e(+/-) channels of sigma(pp -&gt; W+X) X BR(W+ -&gt; e(+) nu(e)) = 144.1 +/- 21.2(stat)(-10.3)(+3.4)(syst) +/- 21.6(norm) pb, and sigma(pp -&gt; W-X) X BR(W- -&gt; e(-) (nu) over bar (e)) = 3.17 +/- 12.1(stat)(-8.2)(+10.1)(syst) +/- 4.8(norm) pb.
  • Adare, A., et al. (författare)
  • Double-spin asymmetry of electrons from heavy-flavor decays in p plus p collisions at root s=200 GeV
  • 2013
  • Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 87:1, s. 012011
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the first measurement of the double-spin asymmetry, A(LL), of electrons from the decays of hadrons containing heavy flavor in longitudinally polarized p + p collisions at root s = 200 GeV for p(T) = 0.5 to 3.0 GeV/c. The asymmetry was measured at midrapidity (vertical bar eta vertical bar &lt; 0.35) with the PHENIX detector at the Relativistic Heavy Ion Collider. The measured asymmetries are consistent with zero within the statistical errors. We obtained a constraint for the polarized gluon distribution in the proton of vertical bar Delta g/g(log(10)(x) = -1.6(-0.4)(+0.5), mu = m(T)(c)vertical bar(2) &lt; 0.030 (1 sigma) based on a leading-order perturbative quantum chromodynamics model, using the measured asymmetry. DOI: 10.1103/PhysRevD.87.012011
  • Adare, A., et al. (författare)
  • Cold-Nuclear-Matter Effects on Heavy-Quark Production at Forward and Backward Rapidity in d + Au Collisions at root s(NN) = GeV
  • 2014
  • Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 112:25, s. 252301
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment has measured open heavy-flavor production via semileptonic decay over the transverse momentum range 1 &lt; p(T) &lt; 6 GeV/c at forward and backward rapidity (1.4 &lt; vertical bar y vertical bar &lt; 2.0) in d + Au and p + p collisions at root s(NN) = 200 GeV. In central d + Au collisions, relative to the yield in p + p collisions scaled by the number of binary nucleon-nucleon collisions, a suppression is observed at forward rapidity (in the d-going direction) and an enhancement at backward rapidity (in the Au-going direction). Predictions using nuclear-modified-parton-distribution functions, even with additional nuclear-p(T) broadening, cannot simultaneously reproduce the data at both rapidity ranges, which implies that these models are incomplete and suggests the possible importance of final-state interactions in the asymmetric d + Au collision system. These results can be used to probe cold-nuclear-matter effects, which may significantly affect heavy-quark production, in addition to helping constrain the magnitude of charmonia-breakup effects in nuclear matter.
  • Adare, A, et al. (författare)
  • Measurement of Long-Range Angular Correlation and Quadrupole Anisotropy of Pions and (Anti)Protons in Central d+Au Collisions at sqrt[s_{NN}]=200 GeV.
  • 2015
  • Ingår i: Physical review letters. - American Physical Society. - 1079-7114. ; 114:19, s. 192301
  • Tidskriftsartikel (refereegranskat)abstract
    • We present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central d+Au and minimum bias p+p collisions at sqrt[s_{NN}]=200 GeV. The charged hadron is measured at midrapidity |?|&lt;0.35, and the energy is measured at large rapidity (-3.7&lt;?&lt;-3.1, Au-going direction). An enhanced near-side angular correlation across |??|&gt;2.75 is observed in d+Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength v_{2} for inclusive charged hadrons at midrapidity up to p_{T}=4.5 GeV/c. We also present the measurement of v_{2} for identified ?^{±} and (anti)protons in central d+Au collisions, and observe a mass-ordering pattern similar to that seen in heavy-ion collisions. These results are compared with viscous hydrodynamic calculations and measurements from p+Pb at sqrt[s_{NN}]=5.02 TeV. The magnitude of the mass ordering in d+Au is found to be smaller than that in p+Pb collisions, which may indicate smaller radial flow in lower energy d+Au collisions.
  • Adare, A., et al. (författare)
  • Centrality categorization Rp(d)+A in high-energy collisions
  • 2014
  • Ingår i: Physical Review C. - Amer Physical Soc. - 0556-2813. ; 90:3, s. 034902
  • Tidskriftsartikel (refereegranskat)abstract
    • High-energy proton- and deuteron-nucleus collisions provide an excellent tool for studying a wide array of physics effects, including modifications of parton distribution functions in nuclei, gluon saturation, and color neutralization and hadronization in a nuclear environment, among others. All of these effects are expected to have a significant dependence on the size of the nuclear target and the impact parameter of the collision, also known as the collision centrality. In this article, we detail a method for determining centrality classes in p(d) + A collisions via cuts on the multiplicity at backward rapidity (i.e., the nucleus-going direction) and for determining systematic uncertainties in this procedure. For d + Au collisions at root s(NN) = 200 GeV we find that the connection to geometry is confirmed by measuring the fraction of events in which a neutron from the deuteron does not interact with the nucleus. As an application, we consider the nuclear modification factors Rp(d)+A, for which there is a bias in the measured centrality-dependent yields owing to auto correlations between the process of interest and the backward-rapidity multiplicity. We determine the bias-correction factors within this framework. This method is further tested using the HIJING Monte Carlo generator. We find that for d + Au collisions at root s(NN) = 200 GeV, these bias corrections are small and vary by less than 5% (10%) up to p(T) = 10 (20) GeV/c. In contrast, for p + Pb collisions at v root s(NN) = 5.02 TeV we find that these bias factors are an order of magnitude larger and strongly pT dependent, likely attributable to the larger effect of multiparton interactions.
  • Adare, A., et al. (författare)
  • Cold-Nuclear-Matter Effects on Heavy-Quark Production in d+Au Collisions at root S-NN=200 GeV
  • 2012
  • Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 109:24, s. 242301
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d + Au and p + p collisions at root S-NN = 200 GeV in the transverse-momentum range 0.85 &lt;= p(T)(e) &lt;= 8.5 GeV/c. In central d + Au collisions, the nuclear modification factor R-dA at 1.5 &lt; p(T) &lt; 5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p + p collisions, and shows that the mass-dependent Cronin enhancement observed at the Relativistic Heavy Ion Collider extends to the heavy D meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the pi(0) and heavy-flavor-electron nuclear modification factors R-AA. DOI: 10.1103/PhysRevLett.109.242301
  • Adare, A., et al. (författare)
  • Cross section for b(b)over-bar production via dielectrons in d plus Au collisions at root s(NN)=200 GeV
  • 2015
  • Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 91:1, s. 014907
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a measurement of e(+)e(-) pairs from semileptonic heavy-flavor decays in d + Au collisions at root s(NN) = 200 GeV. By exploring the mass and transverse-momentum dependence of the yield, the bottom decay contribution can be isolated from charm, and quantified by comparison to PYTHIA and MC@NLO simulations. The resulting b (b) over bar -production cross section is sigma(dAu)(b (b) over bar) = 1.37 +/- 0.28 (stat) +/- 0.46 (syst) mb, which is equivalent to a nucleon-nucleon cross section of sigma(NN)(b (b) over bar) = 3.4 +/- 0.8 (stat) +/- 1.1 ( syst) mu b.
  • Adare, A., et al. (författare)
  • Nuclear Modification of psi ', chi(c), and J/psi Production in d plus Au Collisions at root s(NN)=200 GeV
  • 2013
  • Ingår i: Physical Review Letters. - Amer. Physical Soc.. - 0031-9007. ; 111:20, s. 202301
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results for three charmonia states (psi&#39; chi(c), and J/ psi) in d + Au collisions at vertical bar y vertical bar &lt; 0.35 and root s(NN) = 200 GeV. We find that the modification of the psi&#39; yield relative to that of the J/ psi scales approximately with charged particle multiplicity at midrapidity across p + A, d + Au, and A + A results from the Super Proton Synchrotron and the Relativistic Heavy Ion Collider. In large-impact-parameter collisions we observe a similar suppression for the psi&#39; and J/ psi, while in small-impact-parameter collisions the more weakly bound psi&#39; is more strongly suppressed. Owing to the short time spent traversing the Au nucleus, the larger psi&#39; suppression in central events is not explained by an increase of the nuclear absorption owing to meson formation time effects.
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