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Suppression of Hadrons at Forward Rapidity at RHIC

STAR. Suppression of Hadrons at Forward Rapidity at RHIC. M. Grosse Perdekamp , UIUC. 47 th Recontres De Moriond QCD and High Energy Interactions La Thulie March 10 h –17 th 2012. Final State of a Au-Au Collision in STAR.

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Suppression of Hadrons at Forward Rapidity at RHIC

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  1. STAR Suppression of Hadrons at Forward Rapidity at RHIC M. Grosse Perdekamp, UIUC 47thRecontres De Moriond QCD and High Energy Interactions La Thulie March 10h–17th 2012 Final State of a Au-Au Collision in STAR

  2. A-A Collisions at RHIC and the Initial State Jet quenching, Elliptic flow, J/ψ Studying the Initial State in d-A Collisions Hadron cross sections, hadron pair correlations Summary & Outlook: p-A at LHC and e-A at EIC Outline: Hadron Suppression at Forward Rapidities Initial State in HI Collisions observed final state initial state partonic matter hadronization Au Au time

  3. J/ψ Production: Some Relevant Cold Nuclear Matter Effects in the Initial State high x low x (II) Dissociation of into two D mesons by nucleus or co-movers (I) Shadowing (from fits to DIS data or model calculations) RGPb (III) Gluon saturation from non-linear gluon interactions for the high gluon densities at small x K. EskolaH. Paukkumen, C. Salgado JHEP 0807:102,2008  DGLAP LO analysis of nuclear pdfs GPb(x,Q2)=RGPb(x,Q2)Gp(x,Q2)

  4. J/ψ : Most of the Suppression in A-A is from Cold Nuclear Matter Effects found in d-A Collisions EKS shadowing + dissociation: use d-Au data to determine break-up cross section EKS shadowing + dissociation: from d-Au vs Au-Au data at forward-rapidity EKS shadowing + dissociation: from d-Au vsAu-Au data at mid-rapidity PRC 77,024912(2008)

  5. (III) cont’d The Color Glass Condensate see for example, F. Gelis, E. Iancu, J. Jalilian- Marian, R. Venugopalan, arXiv:1002.0333 CGC: an effective field theory: Small-x gluons are described as the color fields radiated by fast color sources at higher rapidity. This EFT describes the saturated gluons (slow partons) as a Color Glass Condensate. The EFT provides a gauge invariant, universal distribution, W(ρ): W(ρ) ~ probability to find a configuration ρ of color sources in a nucleus. The evolution of W(ρ) is described by the JIMWLK equation. gluon density saturates for large densities at small x : Non-linear evolution eqn. diffusion g-g merging g emission • g-g merging large if • saturation scale • QS, nuclear enhancement ~ A1/3

  6. CGC Expectations for Nuclear Modification of HadronCross Sections in d-Au Collisions Nuclear Modification Factor: RdA CGC-based expectations Kharzeev, Kovchegov, and Tuchin, Phys.Rev.D68:094013,2003 • gluon saturation at low x •  RdAu decreases • at forward rapidity • measure RdAufor • different hadrons: • h+,-, π0, J/ψ rapidity, y pT

  7. BRAHMS d+Au Cross Sections Decrease with Increasing Rapidity and Centrality BRAHMS, PRL 93, 242303 RdAu Hadron production is suppressed at large rapidity consistent with saturation effects at low x in the Au gluon densities  CGC Similar results from PHOBOS, STAR and PHENIX

  8. Theory vs Data CGC p+p d+Au J. Albacete and C. Marquet, PLB687, 184 Not bad! However, different K factors for h+,- in BRAHMS and π0 in STAR

  9. Theory vs Data  Cronin + Shadowing + E-loss I.Vitev, T. Goldman, M.B. Johnson, JW. Qiu, Phys. Rev. D74 (2006) Not bad either! • RdAresults alone do not uniquely demonstrate gluon • saturation. Competing explanations can account for • observed hadron suppression in d-Au at forward rapidity !

  10. Probing for Gluon Saturation Effects with Hadron-HadronCorrelations in d+Au dense gluon field -- Au dilute partonsystem -- d jet with trigger hadron • Experimental signature: • Angular correlation • between hadrons in opposing • hemispheres • widening of correlation width of • d-Au compared to pp • reduction in associated yield • of hadrons on the away site • Effects large at low x •  forward rapidity •  forward EMC upgrades in • STAR : 2 < η < 4 • PHENIX : 3.1 < |η| < 3.8 jet with associated hadron pT is balanced by many gluons Idea: Presence of dense gluon field in the Au nucleus leads to scattering of multiple gluons and partoncan distribute its energy to many scattering centers  Mono-jet signature ! D. Kharzeev, E. Levin, L. McLerran, Nucl.Phys.A748:627-640,2005

  11. PHENIX Muon Piston Calorimeter Technology  ALICE(PHOS) PbWO4 avalanche photo diode readout Acceptance: 3.1 < η < 3.9, 0 < φ < 2π -3.7 < η < -3.1, 0 < φ < 2π Both detectors were installed for 2008 d-Au run. Assembly at UIUC PbWO4 + APD + Preamp MPC integrated in the piston of the muon spectrometer magnet. 11

  12. Use of Forward Calorimeter for the Measurement of di-Hadron Correlations merged p0s PHENIX central spectrometer magnet mid-fwdxgluon ~ 10-2 mid-fwdxgluon ~ 10-2 fwd-fwdxgluon~ 10-4-10-3 ϕ MuonPiston Calorimeter (MPC) trigger EM-cluster 3.1<η<3.9 d Au asssociated p0or EM-clusters 3.1 < η < 3.9 MPC PbWO4 asssociated p0 3.1 < η < 3.9 p0 trigger p0or h+/- |η|<0.35 Backward direction (South)  Forward direction (North)  Side View

  13. Di-Hadron Conditional Yield CY and JdA mid-fwd ConditionalYield Correlated Npair Sgl-Hadron Nuclear Modification factor Di-Hadron Nuclear Modification factor • Possible indicators of nuclear effects • JdA< 1, RdA < 1 ( only mono-jets JdA ~ 0 ) • angular de-correlation of widths Df

  14. STAR 2008 d-Au π0 Forward - Forward Correlations (rad) (rad) pp data dAu data s(dAu)-s (pp)=0.52±0.05 Strong azimuthal broadening from pp to dAu for away side, whilenear side remains unchanged.

  15. Comparison to CGC Prediction CGC prediction for b=0 (central collisions) by CyrilleMarquet Nucl.Phys.A796:41-60,2007 dAu Central Strong suppression of away side peak in central dAuis consistent with CGC prediction

  16. PHENIX JdAStrong Suppression for Central Collisions at Lowxfrag ! PHENIXJdAvsxfragno Suppression for Peripheral Collisions ! Forward-Forward Mid-Forward 60-88% (Peripheral) Trig pT: 0.5-7 GeV/c Trig pT: 1.1-2.0 GeV/c 0-20% (Central) • Back-to-back hadron (jet) • suppression is large at low-x • for central collisions •  mono-jet like ?! •  CGC ? Shadowing + E-loss? PHENIX Phys.Rev.Lett. 107 (2011) 172301 Note: points for mid-fwd JdA are offset for visual clarity

  17. JdAvspQCD, Shadowing and Energy Loss Z.-B.Kang, I. Vitev, H. Xing arXiv:1112.6021 JdAu • pQCD + shadowing • + initial and final • state energy loss • JdA < 1 is not • a unique CGC • signature

  18. Leading Order JdA ~ RGAU  JdA ~ RGAu Low x, mostly gluons Eskola , Paukkunen, Salgado, JHP04 (2009)065 Mid-Forward Forward-Forward 60-88% (Peripheral) 0-20% (Central) b=0-100% Q2 = 4 GeV2 EPS09 NLO gluons xAu High x, mostly quarks Weak effects expected

  19. Summary & Future Steps Towards GA(x) and knowing the Initial State of HI Collisions o RHIC data on single and di-hadron suppression suggest large nuclear effects in the initial state of HI collisions. o A detailed theoretical analysis of the available data yet has to be carried out. o Next: Hadron and Jet measurements in p-Pb at the LHC o Future: GA(x) measurements at an electron-ion collider e+A whitepaper (2007) Precise extraction of GA(x,Q2) from FL measurements at EIC will be able to dis- criminate between different models eRHIC: 10 GeV + 100 GeV/n - estimate for 10 fb-1

  20. Backup Slides

  21. Why Study Nuclear Effects in Nucleon Structure in Particular the Nuclear Gluon Distribution GA(x) ? General interest: • Extend Understanding • of QCD into the non- • perturbative regime of • high field strengths and • large gluon densities. • Search for universal properties of nuclear • matter at low x and high • energies. Heavy Ion Collisions: • Understand the initial state to obtain quantitative • description of the final state • in HI-collisions. • Establish theoretical framework to describe initial state of HI-collisions based • on measurements of GA (x) in p/d-A or e-A.

  22. Jet Quenching: Initial State Saturation of GA(x) or QGP Final State Effect ? PHENIX RAuAu and RdAu for π0 (from 2002 Au-Au and 2003 d-Au runs) Quantify nuclear effects in hadron production Nuclear modification factor: RAA Two explanations for RAuAu < 1 (I) suppression of nuclear GA (x) (II) final state effects of strongly interacting partonic matter Control measurement of RdAu ~ 1  final state effect! RdAu ~ 1 RAuAu < 1

  23. Elliptic Flow v2 : Choice of Initial State GA(x) has Large Impact on Hydro Calculations PHOBOS v2vs Hydro Calculations Color Glass Condensate Brodsky-Gunion-Kuhn Model Phys.Rev.Lett.39:1120  Knowledge of the initial state is important for the quantitative interpretation of experimental results in heavy ion collisions! T. Hirano, U. Heinz, D. Kharzeev, R. Lacey, Y. Nara Phys.Lett.B636:299-304,2006

  24. Probing Low x withCorrelation Measurements for Neutral Pions PYTHIA p+p study, STAR, L. Bland Trigger forward p0 Forward-forward di-hadron correlations reach down to <xg> ~ 10-3 With nuclear enhancement xg ~ 10-4 FMS TPC Barrel EMC hassogives handle on xgluon FTPC

  25. Alternative Explanation of Rapidity-Separated di-Hadron correlations in d+Au Complete (coherent + multiple elastic scattering) treatment of multiple parton scattering gives suppression of pairs with respect to singles for mid-rapidity tag! However, small for forward trigger particle! J. Qiu, I. Vitev, Phys.Lett.B632:507-511,2006

  26. The STAR FMS Upgrade and Configuration for Run 2008 STAR see A. Ogawa H2, Sunday 11:57 BEMC: -1.0 <  < 1.0 TPC: -1.0 <  < 1.0 FMS: 2.5 <  < 4.1 Forward Meson Spectrometer (FMS) Pb-glass EM calorimeter ~x50 more acceptance

  27. Observations at PHENIX using the 2003 d-Au sample: Left: IdA for hadrons1.4 < |h| < 2.0 , PHENIX muon arms. correlated with h+/- in |h| < 0.35, central arms. Right: Comparison of conditional yields with different trigger particle pseudo-rapidities and different collision centralities  No significant suppression or widening seen within large uncertainties ! IdAu from the PHENIX Muon Arms pTa, h+/- pTt, hadron 0-40% centrality 40-88% centrality IdA Trigger pT range IdA Phys.Rev.Lett. 96 (2006) 222301 pTaassociated

  28. The MPC can reliably detect pions (via p0g g) up to E =17 GeV To go to higher pT, use single clusters in the calorimeter Use p0s for 7 GeV < E < 17 GeV Use clusters for 20 GeV < E < 50 GeV Correlation measurements are performed using p0s, clusters Use event mixing to identify pions: foreground  photons from same event background  photons from different events MPC Pion/Cluster Identification South MPC Foreground 12 < E < 15 Background N Yield Minv (GeV/c2)

  29. Cuts Cluster Cuts Cluster ecore > 1.0 (redundant w/ pion assym and energy cuts) Pi0 pair E > 6 GeV Asym < 0.6 Separation cuts to match fg/bg mass distribution Max(dispx, dispy) < 2.5 Use mixed events to extract yields Normalize from 0.25-0.4 presently MPC Pion Selection

  30. MPC pi0 ID Mass window of 0.1-0.2 GeV + previously shown cuts 7 – 17 GeV energy range Max(dispx,dispy) <= 2.5 Charged Hadron ID Track Quality == 31 or 63 n0 <0 Rich cut pT < 4.7 GeV pc3 sdz and sdphi matching < 3 -70 < zed < 70 EMC pi0 Alpha < 0.8 PbGl min E = 0.1, PbSc min E = 0.2 Chi2 cut of 3, prob cut of 0.02 Sector matching Mass window 0.1-0.18 Trigger bit check MPC/CA Cuts

  31. Similar Results from STAR, PHENIX and PHOBOS PRL 94, 082302 Suppression in the d direction and enhancement in the Au fragmentation region d  x1 Au  x2 x1 >> x2 for forward particle, xg = x2  0

  32. STAR Run8 FMS : π0 Forward - Forward Correlations (rad) (rad) pp data dAu data s(dAu)-s (pp)=0.52±0.05 Strong azimuthal broadening from pp to dAu for away side, whilenear side remains unchanged.

  33. Centrality Dependence dAu all data dAuperipheral Azimuthaldecorrelations show significant dependence on centrality! dAucentral

  34. Comparison to CGC prediction CGC prediction for b=0 (central) by CyrilleMarquet Nucl.Phys.A796:41-60,2007 dAu Central Strong suppression of away side peak in central dAuis consistent with CGC prediction

  35. CGC Calculations K. Tuchin arXiv:09125479 dAu pp dAu-peripheral dAu-central

  36. EIC: 4 Key Measurements in e+A Physics • Momentum distribution of gluons in nuclei? Extract via scaling violation in F2 Direct Measurement: FL ~ xG(x,Q2) Inelastic vector meson production Diffractive vectormeson production • Space-time distribution of gluons in nuclei? Exclusive final states Deep Virtual Compton Scattering F2, FL for various impact parameters • Role of colour-neutral (Pomeron) excitations? Diffractive cross-section Diffractive structure functions and vector meson productions Abundance and distribution of rapidity gaps • Interaction of fast probes with gluonic medium? Hadronization, Fragmentation Energy loss CGC EFT: will it be possible to carry out a global analysis of RHIC d+A, LHC p+A and EIC e+A to extract W(ρ) and thus demonstrate universality of W(ρ) ?

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