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Richard Seto for the PHENIX Collaboration University of California, Riverside

Forward Physics in d+Au Collisions at PHENIX: Cold nuclear matter probed with J/  production and pion correlations. Richard Seto for the PHENIX Collaboration University of California, Riverside Rencontres de Moriond QCD and High Energy Interactions La Thuile , March 20-27, 2011.

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Richard Seto for the PHENIX Collaboration University of California, Riverside

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  1. Forward Physics in d+Au Collisions at PHENIX:Cold nuclear matter probed with J/ production and pion correlations Richard Seto for the PHENIX Collaboration University of California, Riverside Rencontres de MoriondQCD and High Energy Interactions La Thuile, March 20-27, 2011 Thanks to my colleagues from whom I have shameless stolen slides – Particularly Matt Wysocki, Oleg Eyser And Beau Meredith

  2. sQGP – How is it born? • τthermalization<1 fm but RsQGP~10 fm • Explaining uniformity? • Early Universe – inflation • What sets initial condition of the sQGP? • Pre equilibrium interactions ? • Turbulence • Strongly coupled (AdS/CFT) • Weakly coupled (pQCD) • What does the initial state look like? • Structure functions ? • BUT in the nucleus they are altered • In particular gluons x < 0.01 suppressed Why ask about Cold nuclear matter? Cold Nuclear Matter is the initial state of interest* *also interesting in its own right 10 fm τthermalization< 1 fm Look at 2 models xG(x) x

  3. Model 1: gluon PDF and nuclear shadowing Nuclear PDF  proton PDF Fit data on nuclei: SLAC, NMC, EMC DIS+DY+PHENIX midrapidtyπ0 b=0-100%” Lack of data large uncertainly in gluon pdf at low-x gluons Large uncertainty At lox-x x Eskola , Paukkunen, Salgado, JHP04 (2009)065 We will add two things: Assume linear dependence on density-weighted longitudinal nuclear thickness  impact parameter (centrality) dependence

  4. Model 2: The Color Glass Condensate (CGC) • Saturation of low-x gluons • high density Recombination of gluons, hence suppression @ low-x • Characterized by QS • Nuclear Amplification  xGA=A1/3xGp • We can exploit this behavior vs centrality • Region of validity: low-x (forward rapidity) Min-bias Cartoon Central

  5. Confuses experimentalists Comments: • plethora of effects e.g. Coherence, Higher twist effects, Initial state energy loss • The CGC is a full QCD calculation in a particular limit which should include all such effects • Worry : CGC is a non-perturbative but weakly coupled theory and requires αS(QS) to be “small”. Much of the bulk (which makes up the sQGP) may be from regions where αS is large • Saturation calculation at strong coupling using AdS/CFT Iancu, NPA(2011) 18. (a conformal theory with lots of other stuff – but αS doesn’t change much at the phase transition...) Strong coupling

  6. Lets first look at the J/ e+ • g+g J/ψ dominant @RHIC Nice coverage in y or equivalently x(Au) forward yx~0.005mid yx~0.03backward yx~0.1 Au d e- μ+ μ- Central Arms μ+ • e+e- -0.35<<0.35 • μ+μ- 1.2<||<2.4 μ- forward back mid

  7. J/ dN/dy vs. rapidity • d+Auis scaled by 1/Ncoll • Ncoll=number of binary collisions • Suppression clearly visible • Now divide p+p d+Au d Au arXiv:1010.1246

  8. RdAu for minimum bias collisions RdAu(0-100%) Significant suppression at mid and forward rapidities. Now compare to the models.. y Bars = point-to-point uncorrelated uncertainties Boxes = point-to-point correlated uncertainties

  9. RdAu for minimum bias collisions Compare to Model 1: EPS09 nuclear PDF + sbr = 4 mb (red curves). sbris the only free parameter. Reasonable agreement Dashed lines are the maximum variation included in EPS09. Note: EPS09, as published, is averaged over all b and we get decent agreement with RdAu(0-100%).

  10. What about the CGC? Kharzeev and Tuchin NPA 770(2006) 40  • Include gluon saturation at low x • (affects forward rapidity) • Enhancement from double gluon ____exchange with nucleus at midrapidity  We can break the data down further by dividing events into small and large impact parameter.

  11. RdAu central and peripheral Model I: EPS09 nuclear PDF + sbr = 4 mb is now deviating from the peripheral data peripheral Gluon saturation again matches the forward rapidity points relatively well, but not mid-rapidity central We can further reduce systematicsby taking the ratio.

  12. RCP peripheral RCP has the advantage of cancelling most of the systematic uncertainties. Now with reduced errors Model I with the nuclear PDF and σbreakup=4mb does not match the data The CGC model works at least in the forward region central • Is there something else we can look at which • might be directly related to the condensate?

  13. Pion Correlations • Gluons overlap and make a condensate • Incoming quark interacts with condensate coherently • pTbalanced by condensate leading to “monoJets” • Look for single “jets” (actually single particles) with no correlated “jet” on opposite side deuteron p “monoJet” Jet Gluon condensate Au nucleus p Jet

  14. The MPC (Muon Piston Calorimeters) • Particle into MPC • e.g. π0 MPC (3.2> >3.8) pT>2.25 • Choose 2nd particle with pT2>1.75 azimuthally opposite • plot 2 vs x2 PHENIX Central region Side View p0 orclusters Pythia simulation π0 MPC (3.2> >3.8) pT>2.25 πpT2>1.75 MPC p0 or h+/- Central Arms 2 d Au 2nd Particle in central arm: x2 ~ .03 2nd Particle in MPC: x2 ~ .001 Log(x2)

  15. The Nuclear Modification Factor • Correlation function Two-particle distribution Including two-particle acceptance Same side peak will be missing Npairs Coherent QCD Multiple scattering Crucial that we have Models that can Describe many Aspects of the data 0 π 2π (rad) Two sides of the same coin? CGC calculation Kharzeev, Levin, McLerran NPA 748,627(2006) Qiu,Vitev PLB 692, 507(2006)

  16. The Nuclear Modification Factor • Correlation function Two-particle distribution Including two-particle acceptance • Conditional yield Number particle pairs per trigger particle Including acceptance & efficiency • Nuclear modification factor Conditional yield ratio d+A/p+p • Indicators of gluon saturation • IdA < 1 • effect gets stronger with centrality Same side peak will be missing Npairs 0 π 2π (rad)

  17. peripheral to central Central Arm - MPC Correlations <pTa>=2.00 GeV/c p0 (trigger,central)/cluster (associate,forward) pp 2.0 < pTt < 3.0 GeV/c for all plots Correlation Function dAu 60-88% dAu 0-20% Df Consistent with CGC

  18. Both particles in MPC (work in progress) • Correlation Functions • Peripheral events • pp and dAu are same • Central events • dAu looses correlated peak Qualitative agreement with a CGC picture Quantitative Analysis and a publication forthcoming

  19. Summary • The data • J/psi • Unable to reconcile rapidity and centrality dependence with Shadowing + naïve breakup cross section • CGC hypothesis works at forward rapidity • Pion Correlations • Suppression with centrality in central-forward correlations (moderate x) • Suppression with centrality in forward-forward correlations (low-x) in qualitative agreement with CGC model • Closing thoughts • Regime probed in present heavy experiments need new non-pertubative QCD techniques e.g. CGC, AdS/CFT, hydrodynamic codes to explain the data • We must understand Cold Nuclear Matter - the initial condition for the heavy ion reaction – if we are to understand the sQGP

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