L.A. Linden-Levy

Publications (128)297.31 Total impact

• Article: Quadrupole anisotropy in dihadron azimuthal correlations in central d+Au collisions at sqrt(s_NN)=200 GeV

  A. Adare, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander, A. Angerami, K. Aoki, N. Apadula, Y. Aramaki, [......], R. Yang, A. Yanovich, J. Ying, S. Yokkaichi, Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, S. Zhou
  [show abstract] [hide abstract]
  ABSTRACT: The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC) reports measurements of azimuthal dihadron correlations near midrapidity in d+Au collisions at sqrt(s_NN)=200 GeV. These measurements complement recent analyses by experiments at the Large Hadron Collider (LHC) involving central p+Pb collisions at sqrt(s_NN)=5.02 TeV, which have indicated strong anisotropic long-range correlations in angular distributions of hadron pairs. The origin of these anisotropies is currently unknown. Various competing explanations include parton saturation and hydrodynamic flow. We observe qualitatively similar anisotropies at RHIC to those seen at the LHC, and when both are divided by an estimate of the initial-state eccentricity, the anisotropies follow a common multiplicity scaling. This scaling is also found to extend to heavy ion data at RHIC and the LHC, where the anisotropies are widely thought to be due to hydrodynamic flow. The results presented here, at much lower collision energy and with a deuteron projectile (instead of a proton), provide important new information for understanding the origin of these new long-range correlations.
  03/2013;
• Source

  Available from: Sarkis Taroian

  Article: Exclusive rho0 electroproduction on transversely polarized protons

  A. Airapetian, N. Akopov, Z. Akopov, E.C. Aschenauer, W. Augustyniak, A. Avetissian, E. Avetisyan, B. Ball, N. Bianchi, H.P. Blok, [......], C. Vogel, S. Wang, S. Yaschenko, H. Ye, Z. Ye, S. Yen, W. Yu, D. Zeiler, B. Zihlmann, P. Zupranski
  [show abstract] [hide abstract]
  ABSTRACT: The exclusive electroproduction of rho-0 mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target. Spin density matrix elements for this process were determined from the measured production- and decay-angle distributions of the produced rho-0 mesons. These matrix elements embody information on helicity transfer and the validity of s-channel helicity conservation in the case of a transversely polarized target. From the spin density matrix elements, the leading-twist term in the single-spin asymmetry was calculated separately for longitudinally and transversely polarized rho-0 mesons. Neglecting s-channel helicity changing matrix elements, results for the former can be compared to calculations based on generalized parton distributions, which are sensitive to the contribution of the total angular momentum of the quarks to the proton spin.
  Physics Letters B 02/2013; 679:100-105. · 3.95 Impact Factor
• Source

  Available from: Sarkis Taroian

  Article: Hard exclusive electroproduction of π⁺π^-pairs

  A. Airapetian, N. Akopov, Z. Akopov, M Amarian, V.V. Ammosov, A Andrus, E.C. Aschenauer, W. Augustyniak, R. Avakian, A. Avetissian, [......], J Volmer, C. Weiskopf, J Wendland, J. Wilbert, G. Smit, Y Ye, Z Ye, S. Yen, B. Zihlmann, P. Zupranski
  [show abstract] [hide abstract]
  ABSTRACT: Hard exclusive electroproduction of pi(+) pi(-) pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY Legendre moments (P-1) and (P-3) of the angular distributions of pi(+) mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the pi(+) pi(-) invariant mass can be understood as being due to the interference between relative P-wave (isovector) and S-, D-wave (isoscalar) states of the two pions. The increase in magnitude of (P-1) as Bjorken x increases is interpreted in the framework of generalized parton distributions as an enhancement of flavour non-singlet qq exchange for larger values of x, which leads to a sizable admixture of isoscalar and isovector pion pairs. In addition, the interference between P-wave and D-wave states separately for transverse and longitudinal pion pairs has been studied. The data indicate that in the f(2)(1270) region at [Q(2)] = 3 GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.
  Phys.Lett.B599:212-222,2004. 02/2013;
• Article: Cold-Nuclear-Matter Effects on Heavy-Quark Production in d+Au Collisions at sqrt[s_{NN}]=200 GeV.

  A Adare, C Aidala, N N Ajitanand, Y Akiba, H Al-Bataineh, J Alexander, A Angerami, K Aoki, N Apadula, Y Aramaki, [......], R Yang, A Yanovich, J Ying, S Yokkaichi, Z You, G R Young, I Younus, I E Yushmanov, W A Zajc, S Zhou
  [show abstract] [hide abstract]
  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 sqrt[s_{NN}]=200 GeV in the transverse-momentum range 0.85≤p_{T}^{e}≤8.5 GeV/c. In central d+Au collisions, the nuclear modification factor R_{dA} at 1.5<p_{T}<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 π^{0} and heavy-flavor-electron nuclear modification factors R_{AA}.
  Physical Review Letters 12/2012; 109(24):242301. · 7.37 Impact Factor
• Article: Medium modification of jet fragmentation in Au+Au collisions at sqrt(s_NN)=200 GeV measured in direct photon-hadron correlations

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, H. Al-Bataineh, H. Al-Ta'ani, J. Alexander, A. Angerami, [......], G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, O. Zaudtke, A. Zelenski, C. Zhang, S. Zhou, J. Zimányi, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the photon is an excellent approximation to the initial p_T of the jet and the ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_ AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high z_T. The fragment yield at low z_T is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.
  12/2012;
• Article: Upsilon (1S+2S+3S) production in d+Au and p+p collisions at sqrt(s_NN)=200 GeV and cold-nuclear matter effects

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, H. Al-Bataineh, H. Al-Ta'ani, J. Alexander, K. R. Andrews, [......], Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, O. Zaudtke, A. Zelenski, C. Zhang, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: The three Upsilon states, Upsilon(1S+2S+3S), are measured in d+Au and p+p collisions at sqrt(s_NN)=200 GeV and rapidities 1.2<|y|<2.2 by the PHENIX experiment at the Relativistic Heavy-Ion Collider. Cross sections for the inclusive Upsilon(1S+2S+3S) production are obtained. The inclusive yields per binary collision for d+Au collisions relative to those in p+p collisions (R_dAu) are found to be 0.62 +/- 0.26 (stat) +/- 0.13 (syst) in the gold-going direction and 0.91 +/- 0.33 (stat) +/- 0.16 (syst) in the deuteron-going direction. The measured results are compared to a nuclear-shadowing model, EPS09 [JHEP 04, 065 (2009)], combined with a final-state breakup cross section, sigma_br, and compared to lower energy p+A results. We also compare the results to the PHENIX J/psi results [Phys. Rev. Lett. 107, 142301 (2011)]. The rapidity dependence of the observed Upsilon suppression is consistent with lower energy p+A measurements.
  11/2012;
• Article: Erratum: Measurement of transverse single-spin asymmetries for J/psi production in polarized p+p collisions at sqrt(s)=200 GeV [Phys. Rev. D 82, 112008 (2010)]

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander, H. Al-Ta'ani, A. Angerami, K. Aoki, [......], S. Yokkaichi, G. R. Young, I. Younus, Z. You, I. E. Yushmanov, W. A. Zajc, O. Zaudtke, C. Zhang, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: We previously reported [Phys. Rev. D 82, 112008 (2010)] measurements of transverse single-spin asymmetries, A_N, in J/psi production from transversely polarized p+p collisions at sqrt(s)=200 GeV with data taken by the PHENIX experiment at the Relativistic Heavy Ion Collider in 2006 and 2008. Subsequently, we have found errors in the analysis procedures for the 2008 data, which resulted in an erroneous value for the extracted A_N. The errors affected the sorting of events into the correct left/right and forward/backward bins. This produced an incorrect value for the 2008 result, but the 2006 result is unaffected. We have conducted two independent reanalyses with these errors corrected, and we present here the corrected values for the 2008 data and the combined results for 2006 and 2008. The new combined spin asymmetry in the forward region is A_N = -0.026+/-0.026(stat)+/-0.003(sys). Since this asymmetry is consistent with zero, we no longer claim that our results suggest a possible non-zero trigluon correlation function in transversely polarized protons.
  10/2012;
• Source

  Available from: Venktesh Singh

  Article: Evolution of �pi^0 Suppression in Au + Au Collisions from sqrt(s_NN) = 39 to 200 GeV

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, H. Al-Taani, J. Alexander, A. Angerami, K. Aoki, [......], R. Yang, A. Yanovich, J. Ying, S. Yokkaichi, Z. You, I. Younus, I. E. Yushmanov, W. A. Zajc, A. Zelenski, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: Neutral-pion �pi^0 spectra were measured at midrapidity (jyj < 0:35) in Au + Au collisions at sqrt(s_NN) = 39 and 62.4 GeV and compared with earlier measurements at 200 GeV in a transverse-momentum range of 1<pT < 10 GeV/c. The high - pT tail is well described by a power law in all cases, and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding spectra for p + p collisions. The nuclear modification factors (RAA) show significant suppression, with a distinct energy, centrality, and pT dependence. Above pT =7 GeVc, RAA is similar for sqrt(s_NN) = 62.4 and 200 GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe RAA well at 200 GeV fail to describe the 39 GeV data, raising the possibility that, for the same pT region, the relative importance of initial-state effects and soft processes increases at lower energies. The pT range where pi^�0 spectra in central Au + Au collisions have the same power as in p + p collisions is � 5 and 7 GeV/c for sqrt(s_NN) = 200 and 62.4 GeV, respectively. For the sqrt(s_NN) = 39 GeV data, it is not clear whether such a region is reached, and the xT dependence of the xT-scaling power-law exponent is very different from that observed in the sqrt(s_NN) = 62 and 200 GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hard scattered partons to higher pT as the collision energy decreases.
  Physical Review Letters 10/2012; 109:152301. · 7.37 Impact Factor
• Article: Evolution of π^{0} Suppression in Au+Au Collisions from sqrt[s_{NN}]=39 to 200 GeV.

  A Adare, S Afanasiev, C Aidala, N N Ajitanand, Y Akiba, R Akimoto, H Al-Ta'ani, J Alexander, A Angerami, K Aoki, [......], R Yang, A Yanovich, J Ying, S Yokkaichi, Z You, I Younus, I E Yushmanov, W A Zajc, A Zelenski, L Zolin
  [show abstract] [hide abstract]
  ABSTRACT: Neutral-pion π^{0} spectra were measured at midrapidity (|y|<0.35) in Au+Au collisions at sqrt[s_{NN}]=39 and 62.4 GeV and compared with earlier measurements at 200 GeV in a transverse-momentum range of 1<p_{T}<10  GeV/c. The high-p_{T} tail is well described by a power law in all cases, and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding spectra for p+p collisions. The nuclear modification factors (R_{AA}) show significant suppression, with a distinct energy, centrality, and p_{T} dependence. Above p_{T}=7  GeV/c, R_{AA} is similar for sqrt[s_{NN}]=62.4 and 200 GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe R_{AA} well at 200 GeV fail to describe the 39 GeV data, raising the possibility that, for the same p_{T} region, the relative importance of initial-state effects and soft processes increases at lower energies. The p_{T} range where π^{0} spectra in central Au+Au collisions have the same power as in p+p collisions is ≈5 and 7  GeV/c for sqrt[s_{NN}]=200 and 62.4 GeV, respectively. For the sqrt[s_{NN}]=39  GeV data, it is not clear whether such a region is reached, and the x_{T} dependence of the x_{T}-scaling power-law exponent is very different from that observed in the sqrt[s_{NN}]=62 and 200 GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hard-scattered partons to higher p_{T} as the collision energy decreases.
  Physical Review Letters 10/2012; 109(15):152301. · 7.37 Impact Factor
• Article: Double Spin Asymmetry of Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s)=200 GeV

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, H. Al-Ta'ani, J. Alexander, K. R. Andrews, A. Angerami, [......], S. Yokkaichi, J. S. Yoo, Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, A. Zelenski, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: We report on the first measurement of double-spin asymmetry, A_LL, of electrons from the decays of hadrons containing heavy flavor in longitudinally polarized p+p collisions at sqrt(s)=200 GeV for p_T= 0.5 to 3.0 GeV/c. The asymmetry was measured at mid-rapidity (|eta|<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 |Delta g/g(log{_10}x= -1.6^+0.5_-0.4, {mu}=m_T^c)|^2 < 0.033 (1 sigma), based on a leading-order perturbative-quantum-chromodynamics model, using the measured asymmetry.
  09/2012;
• Article: Neutral pion production with respect to centrality and reaction plane in Au+Au collisions at sqrt(s_NN)=200 GeV

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander, K. Aoki, Y. Aramaki, E. T. Atomssa, [......], J. Ying, S. Yokkaichi, Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, C. Zhang, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: The PHENIX experiment has measured the production of neutral pions in Au+Au collisions at sqrt(s_NN)=200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, p_T, to 20 GeV/c. The production ratio of eta/pi^0 is 0.46+/-0.01(stat)+/-0.05(syst), constant with p_T and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the p+p and d+Au values. The production of pi^0 is suppressed by a factor of 5, as in earlier findings. However, with the improved statistical precision a small but significant rise of the nuclear modification factor, R_AA, vs p_T, with a slope of 0.0106+/-^(0.0034)_(0.0029)[GeV/c]^-1, is discernible in central collisions. A phenomenological extraction of the average fractional parton energy loss shows a decrease with increasing p_T. To study the path length dependence of suppression, the pi^0 yield was measured at different angles with respect to the event plane; a strong azimuthal dependence of the pi^0 R_AA is observed. The data are compared to theoretical models of parton energy loss as a function of the path length, L, in the medium. Models based on pQCD are insufficient to describe the data, while a hybrid model utilizing pQCD for the hard interactions and AdS/CFT for the soft interactions is consistent with the data.
  08/2012;
• Article: J/psi suppression at forward rapidity in Au+Au collisions at sqrt(s_NN)=39 and 62.4 GeV

  A. Adare, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, H. Al-Ta'ani, J. Alexander, A. Angerami, K. Aoki, N. Apadula, [......], Y. L. Yamaguchi, R. Yang, A. Yanovich, J. Ying, S. Yokkaichi, Z. You, I. Younus, I. E. Yushmanov, W. A. Zajc, A. Zelenski
  [show abstract] [hide abstract]
  ABSTRACT: We present measurements of the J/psi invariant yields in sqrt(s_NN)=39 and 62.4 GeV Au+Au collisions at forward rapidity (1.2<|y|<2.2). Invariant yields are presented as a function of both collision centrality and transverse momentum. Nuclear modifications are obtained for central relative to peripheral Au+Au collisions (R_CP) and for various centrality selections in Au+Au relative to scaled p+p cross sections obtained from other measurements (R_AA). The observed suppression patterns at 39 and 62.4 GeV are quite similar to those previously measured at 200 GeV. This similar suppression presents a challenge to theoretical models that contain various competing mechanisms with different energy dependencies, some of which cause suppression and others enhancement.
  08/2012;
• Article: Direct photon production in d+Au collisions at sqrt(s_NN)=200 GeV

  A. Adare, S. S. Adler, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, A. Al-Jamel, J. Alexander, A. Angerami, [......], G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, O. Zaudtke, C. Zhang, S. Zhou, J. Zimányi, L. Zolin, X. Zong
  [show abstract] [hide abstract]
  ABSTRACT: Direct photons have been measured in sqrt(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 due to a source other than the initial-state nuclear effects.
  08/2012;
• Article: Cold-nuclear-matter effcts on heavy-quark production in d+Au collisions at sqrt(s_NN)=200 GeV

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander, A. Angerami, K. Aoki, N. Apadula, [......], A. Yanovich, J. Ying, S. Yokkaichi, Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  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 sqrt(s_NN)=200 GeV at the Relativistic Heavy Ion Collider, in the transverse-momentum range 0.85 < pT < 8.5 GeV/c. In central d+Au collisions, the nuclear modification factor R_dA at 1.5 < pT < 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 RHIC 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 pi0 and heavy-flavor-electron nuclear modification factor R_AA.
  08/2012;
• Article: Constraining the initial temperature and shear viscosity in a hybrid hydrodynamic model of $\sqrt{s_{NN}}$=200 GeV Au+Au collisions using pion spectra, elliptic flow, and femtoscopic radii

  R. A. Soltz, I. Garishvili, M. Cheng, B. Abelev, A. Glenn, J. Newby, L. A. Linden Levy, S. Pratt
  [show abstract] [hide abstract]
  ABSTRACT: A new framework for evaluating hydrodynamic models of relativistic heavy ion collisions has been developed. This framework, a Comprehesive Heavy Ion Model Evaluation and Reporting Algorithm (CHIMERA) has been implemented by augmenting UVH 2+1D viscous hydrodynamic model with eccentricity fluctuations, pre-equilibrium flow, and the Ultra-relativistic Quantum Molecular Dynamic (UrQMD) hadronic cascade. A range of initial temperatures and shear viscosity to entropy ratios were evaluated for four initial profiles, $N_{part}$ and $N_{coll}$ scaling with and without pre-equilibrium flow. The model results were compared to pion spectra, elliptic flow, and femtoscopic radii from 200 GeV Au+Au collisions for the 0--20% centrality range.Two sets of initial density profiles, $N_{part}$ scaling with pre-equilibrium flow and $N_{coll}$ scaling without were shown to provide a consistent description of all three measurements.
  08/2012;
• Source

  Available from: Venktesh Singh

  Article: Deviation from quark number scaling of the anisotropy parameter v2 of pions, kaons, and protons in Au+Au collisions at √sNN=200 GeV

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander, K. Aoki, Y. Aramaki, E. T. Atomssa, [......], J. Ying, S. Yokkaichi, Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, C. Zhang, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of the anisotropy parameter v2 of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum pT, and transverse kinetic energy KET at midrapidity (|η|<0.35) in Au + Au collisions at √sNN=200 GeV are presented. Pions and protons are identified up to pT= 6 GeV/c, and kaons up to pT= 4 GeV/c, by combining information from time-of-flight and aerogel Čerenkov detectors in the PHENIX Experiment. The scaling of v2 with the number of valence quarks (nq) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KET/nq in noncentral Au + Au collisions (20–60%), but this scaling remains valid in central collisions (0–10%).
  Physical Review C 06/2012; 85:064914. · 3.31 Impact Factor
• Article: Deviation from quark number scaling of the anisotropy parameter v2 of pions, kaons, and protons in Au+Au collisions at √sNN=200 GeV

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander, K. Aoki, Y. Aramaki, E. T. Atomssa, [......], J. Ying, S. Yokkaichi, Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, C. Zhang, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: Measurements of the anisotropy parameter v2 of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum pT, and transverse kinetic energy KET at midrapidity (|η|<0.35) in Au + Au collisions at √sNN=200 GeV are presented. Pions and protons are identified up to pT= 6 GeV/c, and kaons up to pT= 4 GeV/c, by combining information from time-of-flight and aerogel Čerenkov detectors in the PHENIX Experiment. The scaling of v2 with the number of valence quarks (nq) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KET/nq in noncentral Au + Au collisions (20–60%), but this scaling remains valid in central collisions (0–10%).
  Phys. Rev. C. 06/2012; 85(6).
• Article: Ground and excited state charmonium production in p+p collisions at √s=200 GeV

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander, A. Angerami, K. Aoki, N. Apadula, [......], S. Yokkaichi, Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, O. Zaudtke, C. Zhang, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: We report on charmonium measurements [J/ψ (1S), ψ′ (2S), and χc (1P)] in p+p collisions at √s=200 GeV. We find that the fraction of J/ψ coming from the feed-down decay of ψ′ and χc in the midrapidity region (|y|<0.35) is 9.6±2.4% and 32±9%, respectively. We also present the pT and rapidity dependencies of the J/ψ yield measured via dielectron decay at midrapidity (|y|<0.35) and via dimuon decay at forward rapidity (1.2<|y|<2.2). The statistical precision greatly exceeds that reported in our previous publication [ Phys. Rev. Lett. 98 232002 (2007)]. The new results are compared with other experiments and discussed in the context of current charmonium production models.
  Phys. Rev. D. 05/2012; 85(9).
• Article: Ground and excited state charmonium production in p+p collisions at √s=200  GeV

  A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, H. Al-Bataineh, J. Alexander, A. Angerami, K. Aoki, N. Apadula, [......], S. Yokkaichi, Z. You, G. R. Young, I. Younus, I. E. Yushmanov, W. A. Zajc, O. Zaudtke, C. Zhang, S. Zhou, L. Zolin
  [show abstract] [hide abstract]
  ABSTRACT: We report on charmonium measurements [J/ψ (1S), ψ′ (2S), and χc (1P)] in p+p collisions at √s=200  GeV. We find that the fraction of J/ψ coming from the feed-down decay of ψ′ and χc in the midrapidity region (|y|<0.35) is 9.6±2.4% and 32±9%, respectively. We also present the pT and rapidity dependencies of the J/ψ yield measured via dielectron decay at midrapidity (|y|<0.35) and via dimuon decay at forward rapidity (1.2<|y|<2.2). The statistical precision greatly exceeds that reported in our previous publication [ Phys. Rev. Lett. 98 232002 (2007)]. The new results are compared with other experiments and discussed in the context of current charmonium production models.
  Physical Review D 05/2012; 85:092004. · 4.56 Impact Factor
• Source

  Available from: Sarkis Taroian

  Article: Leading-order determination of the gluon polarization from high-pT hadron electroproduction

  The Hermes collaboration, A. Airapetian, N. Akopov, Z. Akopov, E. C. Aschenauer, W. Augustyniak, R. Avakian, A. Avetissian, E. Avetisyan, S. Belostotski, [......], I. Vilardi, C. Vogel, S. Wang, S. Yaschenko, H. Ye, Z. Ye, W. Yu, D. Zeiler, B. Zihlmann, P. Zupranski
  [show abstract] [hide abstract]
  ABSTRACT: Longitudinal double-spin asymmetries of charged hadrons with high transverse momentum p T have been measured in electroproduction using the Hermes detector at Hera. Processes involving gluons in the nucleon have been enhanced relative to others by selecting hadrons with p T typically above 1 GeV. In this kinematic domain the gluon polarization has been extracted in leading order making use of the model embedded in the Monte Carlo Generator Pythia 6.2. The gluon polarization obtained from single inclusive hadrons in the p T range 1 GeV < p T < 2.5 GeV using a deuterium target is \fracDgg( x , m2 ) = 0.049±0.034( stat )±0.010( sys\text-exp ) - 0.099 + 0.126( sys\text-models ) \frac{{\Delta g}}{g}\left( {\left\langle x \right\rangle, \left\langle {{\mu^2}} \right\rangle } \right) = 0.049\pm 0.034\left( {stat} \right)\pm 0.010\left( {sys\text{-}exp} \right)_{ - 0.099}^{ + 0.126}\left( {sys\text{-}models} \right) at a scale m2 = 1.35\textGe\textV2 \left\langle {{\mu^2}} \right\rangle = 1.35\;{\text{Ge}}{{\text{V}}^2} and x = 0.22 \left\langle x \right\rangle = 0.22 . For different final states and kinematic domains, consistent values of \fracDgg \frac{{\Delta g}}{g} have been found within statistical uncertainties using hydrogen and deuterium targets. KeywordsLepton-Nucleon Scattering
  Journal of High Energy Physics 04/2012; 2010(8):1-47. · 5.83 Impact Factor