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

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

3. Suppression of Hadrons at Forward Rapidity at RHIC 3 J/ψ Production: Some Relevant Cold Nuclear Matter Effects in the Initial State (I) Shadowing (from fits to DIS data or model calculations) high x low x (II) Dissociation of into two D mesons by nucleus or co-movers (III) Gluon saturation from non-linear gluon interactions for the high gluon densities at small x K. Eskola H. Paukkumen, C. Salgado JHEP 0807:102,2008  DGLAP LO analysis of nuclear pdfs R G Pb G Pb (x,Q 2 )=R G Pb (x,Q 2 ) G p (x,Q 2 )

4. Suppression of Hadrons at Forward Rapidity at RHIC 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 PRC 77,024912(2008 ) EKS shadowing + dissociation: from d-Au vs Au-Au data at mid-rapidity EKS shadowing + dissociation: from d-Au vs Au-Au data at forward-rapidity

5. Suppression of Hadrons at Forward Rapidity at RHIC 5 (III) cont’d The Color Glass Condensate see for example, F. Gelis, E. Iancu, J. Jalilian- Marian, R. Venugopalan, arXiv:1002.0333 gluon density saturates for large densities at small x : g emission diffusion g-g merging g-g merging large if  saturation scale Q S, nuclear enhancement ~ A 1/3 Non-linear evolution eqn. 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.

6. Suppression of Hadrons at Forward Rapidity at RHIC 6 CGC Expectations for Nuclear Modification of Hadron Cross Sections in d-Au Collisions Nuclear Modification Factor: CGC-based expectations Kharzeev, Kovchegov, and Tuchin, Phys.Rev.D68:094013,2003 R dA pTpT rapidity, y gluon saturation at low x  R dAu decreases at forward rapidity  measure R dAu for different hadrons: h +,-, π 0, J/ψ

7. Suppression of Hadrons at Forward Rapidity at RHIC BRAHMS, PRL 93, 242303 R dAu BRAHMS d+Au Cross Sections Decrease with Increasing Rapidity and Centrality 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 7

8. Suppression of Hadrons at Forward Rapidity at RHIC Theory vs Data  CGC Not bad! However, different K factors for h +,- in BRAHMS and π 0 in STAR p+p d+Au J. Albacete and C. Marquet, PLB687, 184 8

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

10. Suppression of Hadrons at Forward Rapidity at RHIC Idea: Presence of dense gluon field in the Au nucleus leads to scattering of multiple gluons and parton can distribute its energy to many scattering centers  Mono-jet signature ! D. Kharzeev, E. Levin, L. McLerran, Nucl.Phys.A748:627-640,2005 dilute parton system -- d dense gluon field -- Au Probing for Gluon Saturation Effects with Hadron-Hadron Correlations in d+Au 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 trigger hadron jet with associated hadron p T is balanced by many gluons 10

11. Suppression of Hadrons at Forward Rapidity at RHIC 11 PHENIX Muon Piston Calorimeter Technology  ALICE(PHOS) PbWO 4 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. PbWO4 + APD + Preamp Assembly at UIUC MPC integrated in the piston of the muon spectrometer magnet. 11

12. Suppression of Hadrons at Forward Rapidity at RHIC Use of Forward Calorimeter for the Measurement of di-Hadron Correlations d Au asssociated  0 or EM-clusters 3.1 < η < 3.9 PHENIX central spectrometer magnet Backward direction (South)  Forward direction (North)  Muon Piston Calorimeter (MPC) trigger  0 or h +/- |η|<0.35 Side View mid-fwd x gluon ~ 10 -2 fwd-fwd x gluon ~ 10 -4 -10 -3 trigger EM-cluster 3.1<η<3.9 asssociated  0 3.1 < η < 3.9 mid-fwd x gluon ~ 10 -2 merged  0 s 00 MPC PbWO 4 ϕ 12

13. Suppression of Hadrons at Forward Rapidity at RHIC  mid-fwd Correlated N pair Conditional Yield Di-Hadron Nuclear Modification factor Possible indicators of nuclear effects J dA < 1, R dA < 1 ( only mono-jets  J dA ~ 0 ) angular de-correlation of widths Sgl-Hadron Nuclear Modification factor Di-Hadron Conditional Yield CY and J dA 13

14. Suppression of Hadrons at Forward Rapidity at RHIC pp datadAu data  (dAu)-  (pp)=0.52±0.05 Strong azimuthal broadening from pp to dAu for away side, while near side remains unchanged. (rad) STAR 2008 d-Au π 0 Forward - Forward Correlations 14

15. Suppression of Hadrons at Forward Rapidity at RHIC Comparison to CGC Prediction CGC prediction for b=0 (central collisions) by Cyrille Marquet Nucl.Phys.A796:41-60,2007 dAu Central Strong suppression of away side peak in central dAu is consistent with CGC prediction 15

16. Suppression of Hadrons at Forward Rapidity at RHIC PHENIX J dA vs x frag no Suppression for Peripheral Collisions ! Note: points for mid-fwd JdA are offset for visual clarity 60-88% (Peripheral) Trig p T : 1.1-2.0 GeV/c Trig p T : 0.5-7 GeV/c Forward-ForwardMid-Forward 0-20% (Central) PHENIX J dA Strong Suppression for Central Collisions at Low x frag ! Back-to-back hadron (jet) suppression is large at low-x for central collisions  mono-jet like ?!  CGC ? Shadowing + E-loss? 16 PHENIX Phys.Rev.Lett. 107 (2011) 172301

17. Suppression of Hadrons at Forward Rapidity at RHIC J dA vs pQCD, Shadowing and Energy Loss 17 Z.-B.Kang, I. Vitev, H. Xing arXiv:1112.6021 pQCD + shadowing + initial and final state energy loss  J dA < 1 is not a unique CGC signature J dAu

18. Suppression of Hadrons at Forward Rapidity at RHIC Leading Order J dA ~ R G AU x Au EPS09 NLO gluons Eskola, Paukkunen, Salgado, JHP04 (2009)065 Low x, mostly gluons  J dA  ~ R G Au High x, mostly quarks Weak effects expected 60-88% (Peripheral) 0-20% (Central) Forward-Forward Mid-Forward b=0-100% Q 2 = 4 GeV 2 18

19. Suppression of Hadrons at Forward Rapidity at RHIC Summary & Future Steps Towards G A (x) and knowing the Initial State of HI Collisions 19 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: G A (x) measurements at an electron-ion collider eRHIC: 10 GeV + 100 GeV/n - estimate for 10 fb -1 e+A whitepaper (2007) Precise extraction of G A (x,Q 2 ) from FL measurements at EIC will be able to dis- criminate between different models

20. Suppression of Hadrons at Forward Rapidity at RHIC 20 Backup Slides

21. Suppression of Hadrons at Forward Rapidity at RHIC 21 Why Study Nuclear Effects in Nucleon Structure in Particular the Nuclear Gluon Distribution G A (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 G A (x) in p/d-A or e-A.

22. Suppression of Hadrons at Forward Rapidity at RHIC Jet Quenching: Initial State Saturation of G A (x) or QGP Final State Effect ? PHENIX R AuAu and R dAu for π 0 (from 2002 Au-Au and 2003 d-Au runs) Nuclear modification factor: Quantify nuclear effects in hadron production R AuAu < 1 R dAu ~ 1 R AA Two explanations for R AuAu < 1 (I) suppression of nuclear G A (x) (II) final state effects of strongly interacting partonic matter Control measurement of R dAu ~ 1  final state effect! 22

23. Suppression of Hadrons at Forward Rapidity at RHIC Elliptic Flow v 2 : Choice of Initial State G A (x) has Large Impact on Hydro Calculations Color Glass Condensate T. Hirano, U. Heinz, D. Kharzeev, R. Lacey, Y. Nara Phys.Lett.B636:299-304,2006 PHOBOS v 2 vs Hydro Calculations 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! 23

24. Suppression of Hadrons at Forward Rapidity at RHIC Probing Low x with Correlation Measurements for Neutral Pions PYTHIA p+p study, STAR, L. Bland FTPC TPC Barrel EMC FMS   asso gives handle on x gluon Trigger forward  0 Forward-forward di-hadron correlations reach down to ~ 10 -3 With nuclear enhancement x g ~ 10 -4

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

27. Suppression of Hadrons at Forward Rapidity at RHIC I dAu from the PHENIX Muon Arms Observations at PHENIX using the 2003 d-Au sample: –Left: I dA for hadrons 1.4 < |  | < 2.0, PHENIX muon arms. correlated with h +/- in |  | < 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 ! Phys.Rev.Lett. 96 (2006) 222301 Trigger p T range p T aassociated 0-40% centrality 40-88% centrality I dA p T a, h +/- p T t, hadron

28. Suppression of Hadrons at Forward Rapidity at RHIC The MPC can reliably detect pions (via  0   ) up to E =17 GeV To go to higher p T, use single clusters in the calorimeter –Use  0 s for 7 GeV < E < 17 GeV –Use clusters for 20 GeV < E < 50 GeV Correlation measurements are performed using  0 s, clusters Use event mixing to identify pions: foreground  photons from same event background  photons from different events MPC Pion/Cluster Identification N South MPC M inv (GeV/c 2 ) 12 < E < 15Foreground Background Yield

29. Suppression of Hadrons at Forward Rapidity at RHIC 29 MPC Pion Selection 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

30. Suppression of Hadrons at Forward Rapidity at RHIC 30 MPC/CA Cuts 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 –n 0 <0 Rich cut –p T < 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

31. Suppression of Hadrons at Forward Rapidity at RHIC PRL 94, 082302 Suppression in the d direction and enhancement in the Au fragmentation region Similar Results from STAR, PHENIX and PHOBOS d  x 1 Au  x 2 x 1 >> x 2 for forward particle, x g = x 2  0

32. Suppression of Hadrons at Forward Rapidity at RHIC pp datadAu data  (dAu)-  (pp)=0.52±0.05 Strong azimuthal broadening from pp to dAu for away side, while near side remains unchanged. (rad) STAR Run8 FMS : π 0 Forward - Forward Correlations

33. Suppression of Hadrons at Forward Rapidity at RHIC dAu all data Centrality Dependence dAu central Azimuthal decorrelations show significant dependence on centrality! dAu peripheral

34. Suppression of Hadrons at Forward Rapidity at RHIC Comparison to CGC prediction CGC prediction for b=0 (central) by Cyrille Marquet Nucl.Phys.A796:41-60,2007 dAu Central Strong suppression of away side peak in central dAu is consistent with CGC prediction

35. Suppression of Hadrons at Forward Rapidity at RHIC 35 CGC Calculations K. Tuchin arXiv:09125479 pp dAu dAu-central dAu-peripheral

36. Suppression of Hadrons at Forward Rapidity at RHIC 36 Momentum distribution of gluons in nuclei? Extract via scaling violation in F 2 Direct Measurement: F L ~ xG(x,Q2) Inelastic vector meson production Diffractive vector meson production Space-time distribution of gluons in nuclei? Exclusive final states Deep Virtual Compton Scattering F 2, F L 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) ? EIC: 4 Key Measurements in e+A Physics