1. High p T   and Direct  Production T.C. Awes, ORNL International Workshop on RHIC and LHC Detectors Delphi, Greece, June 9, 2003

2. Theme: “The virtue of   ’s and  ’s” To determine if we have produced deconfined QGP we must separately distinguish initial state effects from final state effects. Once produced,  ’s do not interact -> sensitive to: ( yield goes ) initial parton distributions: Intrinsic k T, k T Broadening, Shadowing, Saturation final state parton/hadron rescatterings: Thermal, Jet/Parton Radiation Experimental virtues (calorimeter measurement): Measure  and   in same detector (get 2 for the price of 1!) Identified particles to very high p T   ’s abundantly produced   mass provides calibration check   ’s will suffer additional final state effects: Rescattering (low p T ), Absorption, k T Broadening, Jet/Parton Energy Loss Highlighted here

3. PHENIX Electromagnetic Calorimeter PbSc Highly segmented lead scintillator sampling Calorimeter Module size: 5.5 cm x 5.5 cm x 37 cm PbGl Highly segmented lead glass Cherenkov Calorimeter Module size: 4 cm x 4 cm x 40 cm Two Technologies - very important for systematic error understanding! Differences: Different response to hadrons Different corrections to get linear energy response Different shower overlap corrections

4. Closer look using the Nuclear Modification Factor R AA Compare A+A to p-p cross sections Nuclear Modification Factor: If no “effects”: R < 1 in regime of soft physics R = 1 at high-p T where hard scattering dominates Suppression: R < 1 at high-p T AA

5. RHIC Year-1 High-P T Hadrons hadron spectra out to p T ~4 GeV/c Nominally expect production through hard scattering, scale spectra from N+N by number of binary collisions Peripheral reasonably well reproduced; but central significantly below binary scaling

6. RHIC Headline News… PHENIX First observation of large suppression of high p T hadron yields

7.  RHIC Run 2:  s=200 GeV/c Au+Au collisions now extend to higher P T h + + h - Au-Au nucl-ex/0304022 PHENIX Preliminary

8. Also measured high-P T   spectra in p+p collisions at 200 GeV/c p-p hep-ex/0304038 Calculations with different (gluon) FF’s (Regions indicate scale uncertainty) Spectra for  0 out to 12 GeV/c compared to NLO pQCD predictions. Very good agreement! No intrinsic k T included. Good news for Direct  measurement!

9. R AA : High P T Suppression to at least 10 GeV/c nucl-ex/0304022, submitted to PRL Binary scaling Participant scaling Factor 5 Large suppression in central AuAu - close to participant scaling at high P T

10. Centrality Dependence of R AA More central collisions D.Kharzeev, E.Levin, L.McLerran hep-ph/0210332 nucl-ex/0304022, submitted to PRL The suppression increases smoothly with centrality - approximate N part scaling. Centrality dependence similar to predictions of Color Glass Condensate - Initial state effect!

11. p+A and d+A: The control experiments Nucleus- nucleus collision Proton/deuteron nucleus collision Nuclear effects other than a dense medium are known to affect hadron spectra (e.g. shadowing, Cronin effect) in p+A and d+A collisions, which do not have a created medium. Could these other influences be causing the suppression of high-P T hadrons in Au+Au collisions? If so, then we should also see suppression of high-P T hadrons in d+Au collisions.

12. High P T Spectra in d+Au Collisions PHENIX PRELIMINARY dAu min bias + EMC trigger p T [GeV/c]

13. Neutral pions are measured with 2 independent Calorimeters – PbSc and PbGl PHENIX Preliminary 1  errors - 2 results agree within errors - Not suppressed relative to binary scaling! Neutral Pion R AA for d+Au: R dA The dAu results suggest that the created medium is responsible for hadron suppression in Au+Au

14. “Cronin” enhancement more pronounced in the charged hadron measurement Possibly a larger effect in protons at medium p T ? Particle ID is important! PHENIX Preliminary 1  errors R dA for charged hadrons compared to  0 (h + +h - )/2

15. Data vs Theory :  0 PHENIX Preliminary  0 d+Au (minbias) 200 GeV  0 Au+Au (0-5%) 200 GeV Au+Au: I. Vitev and M. Gyulassy, hep-ph/0208108, to appear in Nucl. Phys. A; M. Gyulassy, P. Levai and I. Vitev, Nucl. Phys. B 594, p. 371 (2001). Shadowing Anti-shadowing d+Au: I. Vitev, nucl-th/0302002 and private communication. Energy loss + Shadowing + Cronin = flat R AA Explains both AuAu and dAu

16. Nuclear modification factor:  s NN dependence A.L.S.Angelis PLB 185, 213 (1987) WA98, EPJ C 23, 225 (2002) PHENIX, PRL 88 022301 (2002) D.d'E. PHENIX Preliminary QM2002 CERN: Pb+Pb (  s NN ~ 17 GeV),  (  s NN ~31 GeV): Cronin enhancement RHIC: Au+Au (  s NN ~ 130, 200 GeV): x4-5 suppression with respect to N coll N collision scaling N part scaling R AA ~ 0.4 R AA ~0.2 R AA ~ 2.0 R AA ~1.5 Is there no energy loss at SPS energies?  SPS ~ 0.5*  RHIC

17.   and  in WA98 at SPS

18. Fixed Target pA Scaling (Cronin Effect) p+p  pA High P T Nuclear Enhancement: *Cronin effect -> K T Broadening *Large effect at SPS! WA98 Preliminary    p+Pb / p+C

19.  0 Scaling with N Coll (Pb+Pb) central suppressed relative to (Pb+Pb) peripheral *Scales weaker than N Coll *Not Cronin-like ! *Decreases with p T ? WA98 PRL 81 (1998) 4087 EPJ C23 (2002) 225. Central suppressed relative to semi-peripheral Similar to RHIC result! 158 A GeV Pb+Pb

20. Central Pb+Pb Direct  p T Spectrum Compare to proton-induced prompt  results: *Assume hard process - scale with the number of binary collisions (=660 for central). *Assume invariant yield has form f(x T )/s 2 where x T =2p T /s 1/2 for s 1/2 - scaling. Factor ~2 variation in p-induced results. Similar  spectral shape for Pb case, but factor ~2-3 enhanced yield. WA98 nucl-ex/0006007, PRL 85 (2000) 3595.

21. Direct  Comparison to pQCD Calculation NLO pQCD calculations factor of 2-5 below s 1/2 =19.4 GeV p- induced prompt  results. But p-induced can be reproduced by effective NLO (K-factor introduced) if intrinsic k T is included. Same calculation at s 1/2 =17.3 GeV reproduces p-induced result scaled to s 1/2 =17.3 GeV Similar  spectrum shape for Pb case, but factor ~2-3 enhanced yield. WA98 nucl-ex/0006007, PRL 85 (2000) 3595.

22. Photons - k T Broadening pQCD-calculations Fit intrinsic k T in pp (E704) (Q 2 = (2p T ) 2 ) k T - broadening in Pb+Pb Magnitude “consistent“ with expectations from pA Hard processes cannot explain excess at low p T Dumitru et al., hep-ph/0103203. ~ 1.3 -1.5 GeV 2  k T 2 ~ 1 GeV 2

23. Direct  : Comparison to Model Calculations Can be described with EOS with QGP or without QGP Many sources of theoretical uncertainty  intrinsic k T, p  broadening *preequilibrium  QM  rates: (under control!)  HM  rates: in-medium masses *Hydro evolution: flow Need further experimental constraints: *Hadron spectra *dileptons (CERES,NA50)  pA  results (WA98) *Results from RHIC P.Houvinen, et al., PLB 535(2002)109. With pQCD Without pQCD

24. Inclusive  : Peripheral Au+Au PbGl and PbSc consistent Compare with inclusive  spectrum calculated via Monte Carlo with measured   cross section as input…

25. (   )measured / (   )simulated : Peripheral PbGl and PbSc consistent with no  excess in peripheral

26. (   )measured / (   )simulated : Central No photon excess seen within errors Working on better understanding of systematics 1  systematic errors

27. pQCD Direct  predictions for RHIC pQCD prediction Plotted here as  /  Decay ( as with data) pQCD prediction with x5   suppression Expext to see large direct  signal, unless  also suppressed (CGC)!

28. Direct  : Expectations for RHIC & LHC At RHIC & LHC the QM contribution dominates for p T >2-3 GeV/c  0 “suppression” = decay  suppression *Increases Direct/Decay For PHENIX: s 1/2 =200 GeV: *Two times WA98 central sample in PHENIX MinBias *High p T trigger events another x2 increase Steffan & Thoma PLB 510 (2001) 98.

29. Direct   at LHC Large direct  rates to ~100 GeV/c, Large   suppression expected, Direct  measurement will provide a powerful probe at LHC. I.Vitev, M.Gyulassy PRL 89 252301 (2002) Direct  (=  +jet ) in ALICE EMCal in one Pb+Pb LHC run.

30.   separation and identification up to ~100 GeV/c PbW0 4 : Very dense: X 0 < 0.9 cm Good energy resolution (after 6 years R&D): stochastic 2.7%/E 1/2 noise 2.5%/E constant 1.3% Photon Spectrometer PbW0 4 crystal high granularity * 2.2x2.2 cm 2 @ 5m *~ 18 k channels, ~ 8 m 2 * cooled to -25 o C Electromagnetic Calorimeters in ALICE: PHOS

31. Proposed EMCAL |  |<0.7  ~ 120 o large area electromagnetic calorimeter *hadronic energy in TPC + em energy in calorimeter * trigger on jets, improve energy resolution,  -jet coincidences  (P T ) ~15% 100 GeV Jet in Central PbPb Electromagnetic Calorimeters in ALICE: EMCal

32. Summary and Conclusions A strong suppression of hadron production is observed in central Au+Au collisions at RHIC (but protons not suppressed?); possibly due to parton energy loss in medium (not conclusive). The hadron production in d+Au collisions shows no strong suppression of high-P T hadrons. Strongly indicative that suppression effect in Au+Au is due to created QCD medium. Suppression also occurs at SPS energies, but much weaker and obscured by large Cronin effect. Direct  signal observed at SPS in Pb+Pb collisions possibly explained by EOS with QGP, but also consistent with HG. Many ambiguities - poor pQCD description, intrinsic k T effects, etc. Situation will be clearer at RHIC. Due to   suppression, direct  signal at RHIC and LHC should stand out like a beacon!

33. In fond remembrance of Aris…

34. USA Abilene Christian University, Abilene, TX Brookhaven National Laboratory, Upton, NY University of California - Riverside, Riverside, CA University of Colorado, Boulder, CO Columbia University, Nevis Laboratories, Irvington, NY Florida State University, Tallahassee, FL Georgia State University, Atlanta, GA University of Illinois Urbana Champaign, IL Iowa State University and Ames Laboratory, Ames, IA Los Alamos National Laboratory, Los Alamos, NM Lawrence Livermore National Laboratory, Livermore, CA University of New Mexico, Albuquerque, NM New Mexico State University, Las Cruces, NM Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TN University of Tennessee, Knoxville, TN Vanderbilt University, Nashville, TN Brazil University of São Paulo, São Paulo China Academia Sinica, Taipei, Taiwan China Institute of Atomic Energy, Beijing Peking University, Beijing France LPC, University de Clermont-Ferrand, Clermont-Ferrand Dapnia, CEA Saclay, Gif-sur-Yvette IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay LLR, Ecole Polytechnique, CNRS-IN2P3, Palaiseau SUBATECH, Ecole des Mines de Nantes, CNRS-IN2P3, Univ. Nantes Germany University of Münster, Münster Hungary Central Research Institute for Physics (KFKI), Budapest Debrecen University, Debrecen Eötvös Loránd University (ELTE), Budapest India Banaras Hindu University, Banaras Bhabha Atomic Research Centre, Bombay Israel Weizmann Institute, Rehovot Japan Center for Nuclear Study, University of Tokyo, Tokyo Hiroshima University, Higashi-Hiroshima KEK, Institute for High Energy Physics, Tsukuba Kyoto University, Kyoto Nagasaki Institute of Applied Science, Nagasaki RIKEN, Institute for Physical and Chemical Research, Wako RIKEN-BNL Research Center, Upton, NY University of Tokyo, Bunkyo-ku, Tokyo Tokyo Institute of Technology, Tokyo University of Tsukuba, Tsukuba Waseda University, Tokyo S. Korea Cyclotron Application Laboratory, KAERI, Seoul Kangnung National University, Kangnung Korea University, Seoul Myong Ji University, Yongin City System Electronics Laboratory, Seoul Nat. University, Seoul Yonsei University, Seoul Russia Institute of High Energy Physics, Protovino Joint Institute for Nuclear Research, Dubna Kurchatov Institute, Moscow PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg St. Petersburg State Technical University, St. Petersburg Sweden Lund University, Lund 12 Countries; 57 Institutions; 460 Participants

35. BACKUP SLIDES

36. Central/Peripheral Ratio for (Anti)Protons and Pions - No apparent suppression in proton yields for 2 <p T <4 GeV/c - Different production mechanism for protons? Submitted to PRL nucl-ex/030536