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Träfflista för sökning "WFRF:(Mitchell J. T.) "

Sökning: WFRF:(Mitchell J. T.)

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1.
  • Adare, A, et al. (författare)
  • Angular decay coefficients of J /ψ mesons at forward rapidity from p+p collisions at s =510 GeV
  • 2017
  • Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - American Physical Society. - 2470-0010. ; 95:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the first measurement of the full angular distribution for inclusive J/ψ→μ+μ- decays in p+p collisions at s=510 GeV. The measurements are made for J/ψ transverse momentum 2<pT<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 λθ is strongly negative at low pT and becomes close to zero at high pT, while the azimuthal coefficient λφ is close to zero at low pT, and becomes slightly negative at higher pT. The frame-independent coefficient λ is strongly negative at all pT in all frames. The data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.
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2.
  • Adare, A., et al. (författare)
  • Production of omega mesons in p plus p, d plus Au, Cu plus Cu, and Au plus Au collisions at root s(NN)=200 GeV
  • 2011
  • Ingår i: Physical Review C (Nuclear Physics). - American Physical Society. - 0556-2813. ; 84:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment at the Relativistic Heavy Ion Collider has measured omega meson production via leptonic and hadronic decay channels in p + p, d + Au, Cu+ Cu, and Au + Au collisions at root s(NN) = 200 GeV. The invariant transverse momentum spectra measured in different decay modes give consistent results. Measurements in the hadronic decay channel in Cu Cu and Au + Au collisions show that. production has a suppression pattern at high transverse momentum, similar to that of pi(0) and eta in central collisions, but no suppression is observed in peripheral collisions. The nuclear modification factors, R-AA, are consistent in Cu + Cu and Au + Au collisions at similar numbers of participant nucleons.
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3.
  • Adare, A, et al. (författare)
  • Nonperturbative-transverse-momentum effects and evolution in dihadron and direct photon-hadron angular correlations in p+p collisions at s =510 GeV
  • 2017
  • Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - American Physical Society. - 2470-0010. ; 95:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Dihadron and isolated direct photon-hadron angular correlations are measured in p+p collisions at s=510 GeV. Correlations of charged hadrons of 0.7<pT<10 GeV/c with π0 mesons of 4<pT<15 GeV/c or isolated direct photons of 7<pT<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 pout perpendicular to the axis of the trigger particle, which is the high-pT direct photon or π0. Nonperturbative evolution effects are extracted from Gaussian fits to the away-side inclusive-charged-hadron yields for different trigger-particle transverse momenta (pTtrig). The Gaussian widths and root mean square of pout are reported as a function of the interaction hard scale pTtrig to investigate possible transverse-momentum-dependent evolution differences between the π0-h± and direct photon-h± correlations and factorization breaking effects. The widths are found to decrease with pTtrig, 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.
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4.
  • Adare, A., et al. (författare)
  • Direct photon production in d+Au collisions at root s(NN)=200 GeV
  • 2013
  • Ingår i: Physical Review C (Nuclear Physics). - American Physical Society. - 0556-2813. ; 87:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Direct photons have been measured in root s(NN) = 200 GeV d + Au collisions at midrapidity. A wide p(T) range is covered by measurements of nearly real virtual photons (1 < p(T) < 6 GeV/c) and real photons (5 < p(T) < 16 GeV/c). The invariant yield of the direct photons in d + Au collisions over the scaled p + p cross section is consistent with unity. Theoretical calculations assuming standard cold-nuclear-matter effects describe the data well for the entire p(T) range. This indicates that the large enhancement of direct photons observed in Au + Au collisions for 1.0 < p(T) < 2.5 GeV/c is attributable to a source other than the initial-state nuclear effects.
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5.
  • Adare, A., et al. (författare)
  • Nuclear modification factors of phi mesons in d plus Au, Cu plus Cu, and Au plus Au collisions at root s(NN)=200 GeV
  • 2011
  • Ingår i: Physical Review C (Nuclear Physics). - American Physical Society. - 0556-2813. ; 83:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX experiment at the Relativistic Heavy Ion Collider has performed systematic measurements of phi meson production in the K+K- decay channel at midrapidity in p + p, d + Au, Cu + Cu, and Au + Au collisions at root s(NN) = 200 GeV. Results are presented on the phi invariant yield and the nuclear modification factor R-AA for Au + Au and Cu + Cu, and R-dA for d + Au collisions, studied as a function of transverse momentum (1 < p(T) < 7 GeV/c) and centrality. In central and midcentral Au + Au collisions, the R-AA of phi exhibits a suppression relative to expectations from binary scaled p + p results. The amount of suppression is smaller than that of the pi(0) and the. in the intermediate p(T) range (2-5 GeV/c), whereas, at higher p(T), the phi, pi(0), and. show similar suppression. The baryon (proton and antiproton) excess observed in central Au + Au collisions at intermediate p(T) is not observed for the phi meson despite the similar masses of the proton and the phi. This suggests that the excess is linked to the number of valence quarks in the hadron rather than its mass. The difference gradually disappears with decreasing centrality, and, for peripheral collisions, the R-AA values for both particle species are consistent with binary scaling. Cu + Cu collisions show the same yield and suppression as Au + Au collisions for the same number of N-part. The R-dA of phi shows no evidence for cold nuclear effects within uncertainties.
6.
  • Adare, A., et al. (författare)
  • phi meson production in d plus Au collisions at root s(NN)=200 GeV
  • 2015
  • Ingår i: Physical Review C (Nuclear Physics). - American Physical Society. - 0556-2813. ; 92:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The PHENIX Collaboration has measured phi meson production in d + Au collisions at root s(NN) = 200 GeV using the dimuon and dielectron decay channels. The phi meson is measured in the forward (backward) d-going (Au-going) direction, 1.2 < y < 2.2 (-2.2 < y < -1.2) in the transverse-momentum (pT) range from 1-7 GeV/c and at midrapidity vertical bar y vertical bar < 0.35 in the p(T) range below 7 GeV/c. The phi meson invariant yields and nuclear-modification factors as a function of p(T), rapidity, and centrality are reported. An enhancement of phi meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p + p 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.
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7.
  • Adare, A, et al. (författare)
  • Dielectron production in Au + Au collisions at sNN =200 GeV DIELECTRON PRODUCTION in Au + Au COLLISIONS ⋯ A. ADARE et al.
  • 2016
  • Ingår i: Physical Review C: covering nuclear physics. - American Physical Society. - 2469-9985. ; 93:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of e+e- production at midrapidity in Au+Au collisions at sNN=200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (mee<5 GeV/c2) and pair transverse momentum (pT<5 GeV/c) for minimum bias and for five centrality classes. The e+e- yield is compared to the expectations from known sources. In the low-mass region (mee=0.30-0.76 GeV/c2) there is an enhancement that increases with centrality and is distributed over the entire pair pT range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to 2.3±0.4(stat)±0.4(syst)±0.2(model) or to 1.7±0.3(stat)±0.3(syst)±0.2(model) for minimum bias collisions when the open heavy-flavor contribution is calculated with pythia or mc@nlo, respectively. The inclusive mass and pT distributions, as well as the centrality dependence, are well reproduced by model calculations where the enhancement mainly originates from the melting of the ρ meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region (mee=1.2-2.8 GeV/c2), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.
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8.
  • Adare, A, et al. (författare)
  • Dielectron production in Au plus Au collisions at root s(NN)=200 GeV
  • 2016
  • Ingår i: Physical Review C (Nuclear Physics). - American Physical Society. - 0556-2813. ; 93:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of e+e- production at midrapidity in Au+Au collisions at sNN=200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (mee<5 GeV/c2) and pair transverse momentum (pT<5 GeV/c) for minimum bias and for five centrality classes. The e+e- yield is compared to the expectations from known sources. In the low-mass region (mee=0.30-0.76 GeV/c2) there is an enhancement that increases with centrality and is distributed over the entire pair pT range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to 2.3±0.4(stat)±0.4(syst)±0.2(model) or to 1.7±0.3(stat)±0.3(syst)±0.2(model) for minimum bias collisions when the open heavy-flavor contribution is calculated with pythia or mc@nlo, respectively. The inclusive mass and pT distributions, as well as the centrality dependence, are well reproduced by model calculations where the enhancement mainly originates from the melting of the ρ meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region (mee=1.2-2.8 GeV/c2), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.
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9.
  • Adare, A., et al. (författare)
  • Cross section and transverse single-spin asymmetry of eta mesons in p up arrow plus p collisions at root s=200 GeV at forward rapidity
  • 2014
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - American Physical Society. - 1550-2368. ; 90:7
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a measurement of the cross section and transverse single-spin asymmetry (AN) for. mesons at large pseudorapidity from root s = 200 GeV p up arrow + p collisions. The measured cross section for 0.5 < p(T) < 5.0 GeV/c and 3.0 < vertical bar eta vertical bar < 3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries A(N) have been measured as a function of Feynman-x (x(F)) from 0.2 < vertical bar x(F)vertical bar < 0.7, as well as transverse momentum (p(T)) from 1.0 < p(T) < 4.5 GeV/c. The asymmetry averaged over positive x(F) is < A(N)> = 0.061 +/- 0.014. The results are consistent with prior transverse single-spin measurements of forward eta and pi(0) mesons at various energies in overlapping x(F) ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p up arrow + p collisions.
10.
  • Adare, A., et al. (författare)
  • Inclusive cross section and double-helicity asymmetry for pi(0) production at midrapidity in p plus p collisions at root s=510 GeV
  • 2016
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - American Physical Society. - 1550-2368. ; 93:1
  • Tidskriftsartikel (refereegranskat)abstract
    • PHENIX measurements are presented for the cross section and double-helicity asymmetry (A(LL)) in inclusive pi(0) production at midrapidity from p + p collisions at root s = 510 GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The pi(0)A(LL) results follow an increasingly positive asymmetry trend with p(T) and root s with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on pi(0) and jet A(LL) and suggested a positive contribution of gluon polarization to the spin of the proton Delta G for the gluon momentum fraction range x > 0.05. The data presented here extend to a currently unexplored region, down to x similar to 0.01, and thus provide additional constraints on the value of Delta G.
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