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Hot and dense matter: Hard probes from RHIC to LHC

Hot and dense matter: Hard probes from RHIC to LHC. M. van Leeuwen, Utrecht University. Hard probes of QCD matter. Use ‘quasi-free’ partons from hard scatterings. Calculable with pQCD. to probe ‘quasi-thermal’ QCD matter. Interactions between parton and medium: Radiative energy loss

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Hot and dense matter: Hard probes from RHIC to LHC

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  1. Hot and dense matter: Hard probes from RHIC to LHC M. van Leeuwen, Utrecht University

  2. Hard probes of QCD matter Use ‘quasi-free’ partons from hard scatterings Calculable with pQCD to probe ‘quasi-thermal’ QCD matter Interactions between parton and medium: • Radiative energy loss • Collisional energy loss • Hadronisation: fragmentation and coalescence Quasi-thermal matter: dominated by soft (few 100 MeV) partons Use the strength of pQCD to explore QCD matter Sensitive to medium density, transport properties

  3. Energy loss in QCD matter radiated gluon propagating parton m2 QCD bremsstrahlung(+ LPM coherence effects) Transport coefficient l Energy loss Energy loss probes: Density of scattering centers: Nature of scattering centers, e.g. mass: radiative vs elastic loss Or no scattering centers, but fields  synchrotron radiation?

  4. Relativistic Heavy Ion Collider Au+Au sNN= 200 GeV PHENIX STAR RHIC: variety of beams: p+p, d+Au, Au+Au, Cu+Cu Two large experiments: STAR and PHENIX Smaller experiments: PHOBOS, BRAHMS decomissioned Recent years: Large data samples, reach to high pT

  5. Energy loss in QCD matter : no interactions RAA = 1 Hadrons: energy loss RAA < 1 Yield per collision Nuclear modification factor : RAA = 1 C. Vale, K. Okada, Hard Probes 2008 0: RAA≈ 0.2 D. d’Enterria Hard partons lose energy in the hot matter

  6. What can we learn from RAA? p0 spectra Nuclear modification factor PHENIX, PRD 76, 051106, arXiv:0801.4020 This is a cartoon! Hadronic, not partonic energy loss No quark-gluon difference Energy loss not probabilistic P(DE) Ball-park numbers: DE/E ≈ 0.2, or DE ≈ 2 GeVfor central collisions at RHIC Note: slope of ‘input’ spectrum changes with pT: use experimental reach to exploit this

  7. Energy distribution from theory TECHQM ‘brick problem’ L = 2 fm, DE/E = 0.2 E = 10 GeV ‘Typical for RHIC’ ASW: Armesto, Salgado, Wiedemann WHDG: Wicks, Horowitz, Dordjevic, Gyulassy • Not a narrow distribution: • Significant probability for DE ~ E • Conceptually/theoretically difficult T. Renk Significant probability to lose no energy For nuclear collisions, need to fold in geometry

  8. Determining the medium density • For each model: • Vary parameter and predict RAA • Minimize 2 wrt data • Models have different but ~equivalent parameters: • Transport coeff. • Gluon density dNg/dy • Typical energy loss per L: e0 • Coupling constant aS PHENIX, arXiv:0801.1665,J. Nagle WWND08 PQM (Loizides, Dainese, Paic),Multiple soft-scattering approx (Armesto, Salgado, Wiedemann)Realistic geometry GLV (Gyulassy, Levai, Vitev), Opacity expansion (L/l), Average path length WHDG (Wicks, Horowitz, Djordjevic, Gyulassy)GLV + realistic geometry ZOWW (Zhang, Owens, Wang, Wang) Medium-enhanced power corrections (higher twist) Hard sphere geometry AMY (Arnold, Moore, Yaffe) Finite temperature effective field theory (Hard Thermal Loops)

  9. Medium density from RAA +2.1 - 3.2 ^ PQM <q> = 13.2 GeV2/fm +0.2 - 0.5 +270 - 150 ZOWW e0 = 1.9 GeV/fm GLV dNg/dy = 1400 +0.016 - 0.012 +200 - 375 AMY as = 0.280 WHDG dNg/dy = 1400 Quantitative extraction gives medium density to 10-20% Method extracts medium density given the model/calculation Theory uncertainties need to be further evaluated e.g. comparing different formalisms, varying geometry Different models approximately agree – except PQM, high density Density 30-50x cold nuclear matter

  10. Heavy quark suppression light Using non-photonic electrons Expected energy loss M.DjordjevicPRL 94 Wicks, Horowitz et al, NPA 784, 426 PHENIX nucl-ex/0611018, STAR nucl-ex/0607012 Expect: heavy quarks lose less energy due to dead-cone effect Most pronounced for bottom Measured suppression of non-photonic electrons larger than expected • Djordjevic, Phys. Lett. B632, 81 • Armesto, Phys. Lett. B637, 362 Radiative (+collisional) energy loss not dominant? E.g.: in-medium hadronisation/dissociation (van Hees, et al)

  11. Di­hadron correlations Combinatorialbackground 8 < pTtrig < 15 GeV associated pTassoc > 3 GeV  trigger Near side Away side Use di-hadron correlations to probe the jet-structure in p+p, d+Au and Au+Au

  12. Medium density from di-hadron measurement associated  trigger J. Nagle, WWND2008 8 < pT,trig < 15 GeV d-Au IAA constraint DAA constraint DAA + scale uncertainty Au-Au Medium density fromaway-side suppression and single hadron suppression agree Theory: ZOWW, PRL98, 212301 e0=1.9 GeV/fm single hadrons However: • Theory curve does not match d+Au: need to evaluate systematics • Experimental uncertainties will decrease in near future Data: STAR PRL 95, 152301 zT=pT,assoc/pT,trig

  13. Lowering pT: gluon fragments/bulk response  trigger Long. flow Long. flow d+Au, 200 GeV Au+Au 0-10% STAR preliminary Jet-like peak associated 3 < pt,trigger < 4 GeV pt,assoc. > 2 GeV J. Putschke, M. van Leeuwen, et al `Ridge’: associated yield at large  dN/d approx. independent of  Strong - asymmetry suggests effect of longitudinal flow or underlying event

  14. Associated yields from coalescence Recombination of thermal (‘bulk’) partons ‘Shower-thermal’ recombination Baryon pT=3pT,parton MesonpT=2pT,parton Baryon pT=3pT,parton MesonpT=2pT,parton Hot matter Hot matter Hard parton (Hwa, Yang) No jet structure/associated yield Expect large baryon/meson ratio associated with high-pT trigger Expect reduced associated yield with baryon triggers 3 < pT < 4 GeV

  15. Associated baryon/meson ratios pTtrig > 4.0 GeV/c 2.0 < pTAssoc< pTtrig p+p / p++p- C. Suarez et al, QM08 Associated yields Inclusive spectra Au+Au: Baryon enhancement Ridge (large Dh): Baryon enhancement p+p, d+Au: B/M  0.3 Jet (small Dh) B/M  0.3 Baryon/meson ratio in ridge close to Au+Au inclusive, in jet close to p+p Different production mechanisms for ridge and jet?

  16. Parton energy from g-jet and jet reconstruction  second-generation measurements at RHIC Qualitatively: known pQCDxPDF extract `known’ from e+e- Full deconvolution large uncertainties (+ not transparent) Fix/measure Ejet to take one factor out • Two approaches: • g-jet • Jet reconstruction

  17. Direct-g recoil suppression Expected recoil for various P(DE) T. Renk  Measurement sensitive to energy loss distribution P(DE) Need precision to distinguish scenarios 8 < ET,g < 16 GeV 2 < pTassoc < 10 GeV J. Frantz, Hard Probes 2008 A. Hamed, Hard Probes 2008 STAR Preliminary ET,g DAA(zT) IAA(zT) = Dpp(zT) Large suppression for away-side: factor 3-5 Results agree with model predictions Uncertainties still sizable Some improvements expected for final resultsFuture improvements with increased RHIC luminosity

  18. Jet reconstruction in heavy ion events STAR preliminary pt per grid cell [GeV] η j ~ 21 GeV Jets clearly visible in heavy ion events at RHIC Quantitative analysis requires: Good jet-finding algorithm Combinatorial background subtraction • Use different algorithms to estimate systematic uncertainties: • Cone-type algorithms simple cone, iterative cone, infrared safe SISCone • Sequential recombination algorithmskT, Cambridge, inverse kT http://rhig.physics.yale.edu/~putschke/Ahijf/A_Heavy_Ion_Jet-Finder.html FastJet:Cacciari, Salam and Soyez; arXiv: 0802.1188

  19. Jet spectrum – RAA of jets Nbin scaled p+p seed=4.6 GeV R=0.4 Au+Au 0-10% LOHSC dNJet/dET (per event) MB-Trig O HT-Trig dNJet/dET (per event) PyDet PyEmbed PyTrue LOHSC STAR Preliminary R=0.4 pT cut =1 GeV Seed=4.6 GeV Statistical Errors Only ET [GeV] Energy resolution Pythia jet+Heavy ion background Effect of resolution on spectrum Counts pTcut=1.0 GeV Seed=4.6 GeV LOHSC pTcut =1 GeV R=0.4 ET=35±5 GeV S. Salur, Hard Probes 2008 STAR Preliminary ∆E E = EPyDet – EPyTrueE = EPyEmbed - EPyTrue E = EPyEmbed - EPyDet No significant suppression of jet production in AA  Jet reconstruction recovers unbiased jet sample

  20. Jet fragmentation Fragmentation function Fragmentation function ratio A+A/p+p pt,jetrec. >30 GeV STAR preliminary stat. errors only J. Putschke, Hard Probes 2008 pthadron~10 GeV Au+Au HT Et>7.5 GeV p+p HT Et>5.4 GeV Jet-energy uncorrected – needs study No apparent modification in the fragmentation function with respect to p+p

  21. Relating jets and single hadrons High-pT hadrons from jet fragmentation Qualitatively: • Measured suppression of single hadrons: • Suppression of jet yield (out-of-cone radiation) • Modification of fragment distribution (in-cone radiation) First results from STAR show neither Work in progress: Better understanding of interplay between reconstruction biases (trigger bias, background subtraction) and jet-quenching needed Requires theory-experiment collaboration

  22. New development: E-loss generators Event generators treat full in-medium QCD shower: • Theory/model advantage over analytic approach: conserve energy/respect kinematic bounds Important experimental tool: can perform jet reconstruction (and other analysis) on model 2 models JEWEL K. Zapp, U. Wiedemann, arXiv:0804.3568 Focus on collisional energy loss + medium response Cluster hadronisation q-PYTHIA L. Cunqueiro, N. Armesto, C. Salgado, arXiv:0809.4433 Focus on radiative energy loss Modified shower evolution Important step for the field

  23. Transport and medium properties Transport coefficient 2.8 ± 0.3 GeV2/fm (model dependent) e 23 ± 4 GeV/fm3 pQCD: T  400 MeV (Baier) (Majumder, Muller, Wang)  ~5 - 15 GeV/fm3T ~ 250 - 350 MeV Viscosity Total ET t0 = 0.3-1fm/c From v2 (see previous talk: Steinberg) (Bjorken) Lattice QCD: h/s < 0.1 (Meyer) Broad agreement between different observables, and with theory A quantitative understanding of hot QCD matter is emerging

  24. Outlook I: LHC Simulated result ALICE EMCal TDR For example: Can measure jet fragmentation with Ejet = 175 GeV Talks by T. Awes, M. Spousta, L. Sarycheva Use kinematic reach (DE >> E) to determine energy dependence of DE Large hard process yields: Jets to > 200 GeV Light, heavy hadrons to 100 GeV Test/validate understanding gained from RHIC

  25. Outlook II: RHIC Accelerator upgrades Stochastic cooling Detector upgrades Vertex detectors PHENIX Projected performance forg-hadron measurement STAR Enables charm/bottom direct measurements Ongoing data analysis: Large sample Au+Au (run-7) and d+Au (run-8)

  26. Conclusion Hard probes provide insight in nature of hot QCD matter RHIC results: • ‘Standard’ measurements extent to high pT, start to constrain theory in detail • Intermediate pT: interplay between hard and soft physics, e.g. ‘the ridge’ • New large samples: experimental control over Eparton • Gamma-jet analysis • Jet reconstruction DE ~ 2 GeV at RHIC, DE/E not small Start systematic comparisons of different measurements with theory  Assessment of systematics in theory and experiment Progress towards ‘global analysis’ of heavy ion data • Future: • RHIC: larger luminosity, detector upgrades • LHC: Large rates at high pT, exploit DE < E Theory: develop in-medium shower generators

  27. Conclusion Hard probes provide insight in nature of hot QCD matter Recent developments: • Large luminosity at RHIC • Extend to higher pT • Gamma-hadron analysis (fix parton energy) • Jet reconstruction • Near future at LHC • Large rates at high pT, exploit DE < E • Theory: develop in-medium shower generators DE ~ 2 GeV at RHIC, DE/E not small Start combining different measurements to improve understanding - Assessment of systematics in theory and experiment Progress towards ‘global analysis’ of heavy ion data

  28. Extra Slides

  29. Direct-g recoil yields  Run 4 p+p/Au+Au @ 200 GeV M. Nguyen, Quark Matter 2006 A. Hamed, Hard Probes 2008 Direct-g–jet measurements being pursued by STAR and PHENIX Requires large data samples Suppression of away-side yield visible Similar to di-hadrons, but now with selected parton energy

  30. Away-side suppression  A. Hamed et al QM08 Away-side yield AuAu/pp Model predictions tuned to hadronic measurements First g-jet results from heavy ion collisions Measured suppression agrees with theory expectations Next step: measure pTassoc dependence to probe DE distribution

  31. Intermediate pT: the ridge  trigger 3 < pt,trig< 4 GeV/c Jet-like peak 4 < pt,trig < 6 GeV/c pt,assoc. > 2 GeV/c Au+Au 0-10% STAR preliminary Au+Au 0-10% STAR preliminary J. Putschke et al, QM06 `Ridge’: associated yield at large , small Df associated Weak dependence of ridge yield on pT,trig  Relative contribution reduces with pT,trig Strong - asymmetry suggests coupling to longitudinal flow

  32. RAA at LHC GLV BDMPS T. Renk, QM2006 RHIC RHIC S. Wicks, W. Horowitz, QM2006 LHC: typical parton energy > typical E Expected rise of RAA with pT depends on energy loss formalism Nuclear modification factor RAA at LHC sensitive to radiation spectrum P(E)

  33. Baryon/meson ratios p/p ratio Large baryon/meson ratio at intermediate pT  Hadronisation by coalescence of quarks? Expect p mainly from gluons and DEg>DEq, no stronger suppression seen for p Anti-Baryon/meson ratio P. Fachini et al, QM08 Theory: X.-N. Wang, PRC 70, 031901 New data extend pT-range in p+p New STAR results on baryon fragmentation in p+p, see M. Heinz

  34. Heavy-light difference light M.DjordjevicPRL 94 (2004) Expect: dead-cone effect Armesto et al, PRD71, 054027 Wicks, Horowitz et al, NPA 784, 426 Armesto plot Below 10 GeV: charm loses 20-30% less energy than u,d Bottom loses ~80% less Expected suppression of D mesons ~0.5 times light hadrons

  35. Heavy flavour: Discrepancy STAR/PHENIX spectra PHENIX: A/(exp(-a pT - b pT2) + pT/p0)n: A = 377 +/- 60 mb GeV^-2 c^3 a = 0.3565 +/- 0.014 c/GeV b = 0.0680 +/- 0.019 (c/GeV)^2 p0 = 0.70 +/- 0.02 (c/GeV) n = 8.25 +/- 0.04 35 Zhangbu Xu (STAR Collaboration) SQM08

  36. e/p ratio STAR Preliminary STAR Preliminary e+e- STAR Preliminary Conversion in detector material x10 reduced Run8 is consistent with run3 NPE results Run8: 0.55%X0(beampipe 0.29%, air: 0.1%, wrap ~0.14% …) run3: 5.5%X0(+ SVT…) Detector Material is not the issue Jin Fu, Parallel session 12.I Zhangbu Xu (STAR Collaboration) SQM08 36

  37. QCD and quark parton model At high energies, quarks and gluons are manifest At low energies, quarks are confined in hadrons S. Bethke, J Phys G 26, R27 Asymptotic freedom Running coupling: s grows with decreasing Q2 Running coupling: from confinement to asymptotic freedom QCD governs both extremes. Can we study/conceptualise the evolution? Study emergent behaviour at large coupling: confinement, bulk QCD matter

  38. Radiative energy loss in QCD Energy loss process characterized by a single constant kT~m Transport coefficient l Energy loss Transport coefficient sets medium properties pQCD expectation (Baier et al) Non-perturbative: is a Wilson loop (Wiedemann) (Liu, Rajagopal, Wiedemann) From AdS/CFT e.g. N=4 SUSY: Transport coefficient is a fundamental parameter of QCD matter

  39. Some open questions Urs Wiedemann, Hard Probes 2008

  40. Di-hadron suppression in Au+Au d+Au Au+Au 20-40% Au+Au 0-5% pTassoc > 3 GeV pTassoc > 6 GeV High-pT hadron production in Au+Au dominated by (di-)jet fragmentation Suppression of away-side yield in Au+Au collisions Measures energy loss in di-jet events No detectable broadening or change of peak shape: fragmentation after energy loss

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