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Oleg Eyser Beau Meredith, Mickey Chiu, Matthias Perdekamp for the PHENIX Collaboration

DIFFRACTION 2010, Sep. 10-15, Otranto, Italy. Forward Di-Hadron Correlations in d+Au Collisions in PHENIX Searching for Gluon Saturation with the MPC. Oleg Eyser Beau Meredith, Mickey Chiu, Matthias Perdekamp for the PHENIX Collaboration. The gluon density at low x.

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Oleg Eyser Beau Meredith, Mickey Chiu, Matthias Perdekamp for the PHENIX Collaboration

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  1. DIFFRACTION 2010, Sep. 10-15, Otranto, Italy ForwardDi-Hadron Correlationsin d+Au Collisions in PHENIXSearching for Gluon Saturationwith the MPC Oleg Eyser Beau Meredith, Mickey Chiu, Matthias Perdekamp for the PHENIX Collaboration

  2. The gluon density at low x At small x we see an increase in gluons. There must be a kinematic region in which the gluon density reaches a saturation! Bremsstrahlung ~ asln(1/x) Recombination ~ asr

  3. Color Glass Condensate Qs2(x) Saturation Scale Forward Rapidity log x-1 Parton Gas d Au non-perturbative pT is balanced by gluons BKFL DGLAP Mid Rapidity log LQCD2 log Q2 The color glass condensate • Hadronic probe • Couple to gluons • High A • Higher parton densities • Asymmetric • Probe low x

  4. Signatures of the CGC p0 meson |h|<0.35 PHENIX CGC expectations Kharzeev, Kovchegov,,Tuchin, Phys.Rev.D68:094013,2003 increased h BRAHMSSTAR Gluon saturation is not the only explanation for the reduced yields. There may be other effects. PRL 97, 53203 (2006) PRL 98, 172302 (2007)

  5. d+Au in HIJING (A. Ogawa) Au Shadowing in jet correlations • pQCD 2→2 process = back-to-back di-jet • With shadowing in nucleus forward jet p d p mid-rapidity jet Vitev, hep-ph/0405068v2

  6. Mono-jets from the CGC • In the saturation regime the jet pT is balanced by many gluons. Kharzeev, Levin, McLerran (NPA748, 627) d Au dense gluon field • The gluon field is increased in central vs. peripheral collisions.

  7. 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 • Angular de-correlation of widths

  8. BRAHMS pp2pp PHENIX STAR Gluon Saturation @ RHIC d+Au vs p+p high-x valence quarks 0.25 < xq < 0.7 on low-x gluons 0.001 < xg < 0.1 Signatures of saturation • suppressions of nuclear modification factors • angular de-correlations of di-jet signals saturation is expected at x≈10-4

  9. Central Arms | η | < 0.35 Muon Arms 1.2 < | η | < 2.4 Muon Piston Calorimeter 3.1 < | η | < 3.9 Azimuthal Correlations in PHENIX • Trigger particle • Associate particle • Correlation • Near side peak • Away side peak Dj

  10. Azimuthal Correlations (prev.) • 2003 data • Trigger hadron from the muon arms • Correlated hadron from the central arm Phys.Rev.Lett.96:222301,2006

  11. Electromagnetic Calorimetersat rapidity 3.1 < |h| < 3.9 2.2 x 2.2 x 18 cm3 PbWO4 crystals 220 cm from nominal interaction point p0 merging effects pTmax ~ 2 GeV/c at outside ring For higher pT Reconstructed p0s for 7 GeV < E < 22 GeV Clusters for E > 15 GeV (~ 85% p0) The Muon Piston Calorimeters • gg invariant mass distribution • 11 GeV < E < 15 GeV • Signal pairs • Mixed event pairs • p0 yield

  12. peripheral to central Forward Di-jet Signal with Dh = 3.4 PHENIX Central region Side View p0 orclusters p0 or h+/- d Au xgluon ~ 10-2 Aueffective xgluon ~ 10-3

  13. Forward correlations at h = 3.4 PHENIX Central region Side View • Work in progress • Area of away-side peak represents conditional yield • No efficiency correction • No uncorrelated background yet • Conditional yields, widths not shown p0 orclusters d Au xgluon ~ 10-3 Aueffective xgluon ~ 10-4

  14. Forward correlations (minBias) • Trigger particle pT > 2 GeV/c • Associate particle pT > 0.875 GeV/c

  15. Forward correlations peripheral central Peripheral d+Au seems more similar to p+p Central d+Au shows a reduced yield, maybe broadening

  16. pT,trigger pT,associate

  17. pT,trigger pT,associate

  18. Summary • Central/forward di-hadron correlations • No significant broadening between d+Au vs pp • Reduced IdA in more central collisions • Model calculations are needed to understand this effect • Forward/forward di-hadron correlations • Qualitative indications of onset of gluon saturation hypothesis in reduced yields • Data also suggests width broadening • More work needed on uncorrelated background!

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