1. High-p T probes of heavy-ion collisions at RHIC and LHC Marco van Leeuwen, LBNL

2. Marco van Leeuwen, High-p T probes at RHIC and LHC 2 Introduction Motivation: Initial production well-calibrated Hard processes (high Q2) are only sensitive to short distances and times Final state particles (partons and/or hadrons) probe the medium through interactions

3. Marco van Leeuwen, High-p T probes at RHIC and LHC 3 Introduction Can we check our understanding of hard processes? For hard process, expect to scale as number of binary collision N coll for A+A Yes, by showing that p+p results can be explained by pQCD Parton density functionMatrix element Fragmentation function Measured in DIS e+e-e+e- pQCD

4. Marco van Leeuwen, High-p T probes at RHIC and LHC 4 Hard processes at RHIC t High-p t light hadron production – Most abundant process, lots of data – Inclusive production, di-hadron correlations, elliptic flow – Baryon production sensitive to quark vs gluon jets Direct  production – Non-interaction probe, test N coll scaling Heavy quark production – Main results so far from semi-leptonic decays – Test pQCD theory for production and suppression (dead-cone effect) Goal: -Understand production rates and suppression in A+A -Determine medium properties (density, dynamics) in heavy-ion collisions

5. Marco van Leeuwen, High-p T probes at RHIC and LHC 5 RHIC accelerator and experiments PHENIX Focus: rare probes , e ±,  Partial coverage High-granularity calorimetry and tracking Forward muon detectors STAR Focus: global observables Large volume TPC (2  ) +EM calorimetry (coarse) Maximum energy:  s NN =200 GeV for Au+Au  s=500 GeV for p+p (default 200 GeV) Recent runs 2004: large statistics Au+Au (~80M events), most results in this presentation 2005: large statistics Cu+Cu, analysis in progress 2006: dedicated polarised p+p run, data-taking in progress

6. Marco van Leeuwen, High-p T probes at RHIC and LHC 6 p+p jet spectrum @  s=200 GeV First direct measurement of jet spectrum at RHIC Statistics out to p T =50 GeV … more being collected Measured spectrum agrees with NLO pQCD Dominant uncertainty: jet energy scale Prefer particle spectra, di-hadron correlations for Au+Au baseline (backgrounds too large for jet reconstruction in Au+Au)

7. Marco van Leeuwen, High-p T probes at RHIC and LHC 7 Light hadron production in p+p NLO calculations: W. Vogelsang Star, PRL 91, 172302 Brahms, nucl-ex/0403005 Light hadron production at RHIC in good agreement with NLO pQCD Caveat: gluon fragmentation not so well constrained from e + e - PRL 91, 241803

8. Marco van Leeuwen, High-p T probes at RHIC and LHC 8 Baryon production in p+p Albino, Kniehl, Kramer, Nucl Phys B725, 181 hep-ph/0510173 { Proton spectra used to be problematic (KKP FF) New parameterisation of FF (AKK) from full flavour separated datasets (OPAL), (no SU(3) flavour symmetry assumption) shows much better agreement  also well described FF parametrisation is an ongoing activity Baryon production at RHIC also described by pQCD

9. Marco van Leeuwen, High-p T probes at RHIC and LHC 9 Direct photons Direct  in p+p agree with pQCD q + g  q +  PHENIX, PRL 94, 232301 Direct  in A+A scales with N coll Centrality R AA =1 (N coll scaling) for incoherent superposition of p+p collisions Production through q + q  g + 

10. Marco van Leeuwen, High-p T probes at RHIC and LHC 10 Light hadron production in A+A Photons and hadron production measured to well in the (expected) perturbative regime  : R AA = 1  0, h ± : R AA ≈ 0.2 Light hadron production suppressed by factor 4-5 in central Au+Au Au+Au 200 GeV, 0-5% central

11. Marco van Leeuwen, High-p T probes at RHIC and LHC 11 Radiative energy loss in QCD Calculational frameworks: Multiple soft scattering (BDMPS, Wiedemann, Salgado,…) Few hard scatterings,opacity expansion (Gyulassy, Vitev, Levai, Wang,…) Twist expansion (Wang, Wang,…) Plus details: Longitudinal expansion reduces  E~L 2 to  E~L Finite energy effects may lead to E-dependent energy loss Medium properties can be characterized by a single constant e.g. transport coefficient ‘average k T -kick per mean-free-path’  E does not depend on parton energy  E  L 2 due to interference effects (for a static medium) Salgado and Wiedemann, Phys. Rev. D68, 014008  dI/d   ~1 GeV at RHIC  C Soft radiation suppressed by phase space requirement k T <  Radiative energy loss is due to moderate number (~3) of finite energy gluons (  ~0.1-1 GeV)

12. Marco van Leeuwen, High-p T probes at RHIC and LHC 12 Non-perturbative dynamics at intermediate p T Intermezzo Enhancement depends on: - Particle type (different for , p) - Centrality d+Au,  s=200 GeV Hadron production in d+Au enhanced compared to N coll scaling ‘Cronin effect’ known from fixed target at Fermilab, but mechanism unclear Effect small compared to effects in Au+Au  p

13. Marco van Leeuwen, High-p T probes at RHIC and LHC 13 Baryon production in Au+Au Intermediate p T (2-4 GeV) p/  much larger in Au+Au than p+p (vacuum fragmentation) At p t =6 GeV: p/  similar in p+p, d+Au and central Au+Au Non-perturbative effects large at intermediate p T Note: p/  ratio sensitive to gluon/quark ratio. Probes differences in coupling to medium This presentation: focus at highest p T Au+Au, 0-5% central,  s NN =200 GeV

14. Marco van Leeuwen, High-p T probes at RHIC and LHC 14 Hadron suppression:  s NN =200 GeV Au+Au Different calculations lead to similar medium densities dN g /dy=1100,, approx. 30 times nuclear density Reasonable agreement between data and calculations for p T up to 20 GeV High statistics year-4 data

15. Marco van Leeuwen, High-p T probes at RHIC and LHC 15 Centrality dependence Dainese, Loizides and Paic, Eur.Phys.J. C38, 461 (2005) p T >4.5 GeV Data agree with calculated suppression patterns Path length, density dependence leads to centrality dependence of suppression More differential tests (e.g. from v 2 ) are under way On theory side: need to quantify constraints on L-dependence

16. Marco van Leeuwen, High-p T probes at RHIC and LHC 16 Surface emission (geometric bias) ? Inclusive measurements insensitive to opacity of bulk  Need coincidence measurements to probe deeper R AA ~0.2-0.3 for broad range of Large energy loss  opaque core Eskola et al., hep-ph/0406319

17. Marco van Leeuwen, High-p T probes at RHIC and LHC 17 Azimuthal di-hadron correlations Phys Rev Lett 91, 072304 4 < p T,trig < 6 GeV p T,assoc > 2 GeV p+p  trigger associated Au+Au Need to subtract background in Au+Au 2002 result No modification of near side Strong suppression of away side No measurable away-side yield; cannot quantify suppression

18. Marco van Leeuwen, High-p T probes at RHIC and LHC 18 Jet-like di-hadron correlations Larger p T allows quantitative analysis of jet energy loss New results, year-4 Background negligible at higher p T,assoc 8 < p T,trig < 15 GeV Larger data sample extends p T -range Emergence of the away side peak d+AuAu+Au 20-40% 0-5%

19. Marco van Leeuwen, High-p T probes at RHIC and LHC 19 Di-hadron correlations: centrality dependence Fit scaled by x2 8 < p T,trig < 15 GeV/c Near side yields essentially unmodified Away-side: Increasing suppression with centrality Again ‘surface bias’

20. Marco van Leeuwen, High-p T probes at RHIC and LHC 20 Di-hadron fragmentation ~0.54 ~0.25 8 < p T,trig < 15 GeV/c Scaling factors Near side fragmentation unmodified Away-side: strong suppression, but shape similar above z T ≈0.4

21. Marco van Leeuwen, High-p T probes at RHIC and LHC 21 A closer look at azimuthal peak shapes 8 < p T (trig) < 15 GeV/c p T (assoc)>6 GeV Large energy loss without observable modification of longitudinal and azimuthal distributions Observations constrain energy loss fluctuations and geometrical bias No away-side broadening  

22. Marco van Leeuwen, High-p T probes at RHIC and LHC 22 Discussion of di-hadron results Strong suppression (factor 4-5, similar to inclusive hadron suppression) without modification of longitudinal and azimuthal fragmentation shapes In contrast to several model expectations Broadening due to fragments of induced radiation Induced acoplanarity (BDMPS): = STAR preliminary Near-side enhancement due to trigger bias Majumder, Wang, Wang, nucl-th/0412061 Observation: Vitev, hep-ph/0501225

23. Marco van Leeuwen, High-p T probes at RHIC and LHC 23 Confronting I AA and R AA Dainese, Loizides and Paic, QM poster Eskola et al., hep-ph/0406319 I AA ≈ R AA ≈ 0.20-0.25 First look: from I AA and R AA in quantitative agreement ≈ 5-7 GeV 2 /fm in central Au+Au @ RHIC Need to further assess theory uncertainties

24. Marco van Leeuwen, High-p T probes at RHIC and LHC 24 Heavy quark suppression (non-photonic electrons) Suppression of non-photonic electrons larger than expected Compatible with charm-dominance up to p T ≈ 10 GeV Comparison of light and heavy quark suppression elucidates energy loss mechanism Wicks, et al, nucl-th/0512076 Collisional energy loss revisited

25. Marco van Leeuwen, High-p T probes at RHIC and LHC 25 Au+Au 0-5% STAR Preliminary d+Au 100-40% Intermezzo II: Jet structure at intermediate p T 3 < p T,trig < 6 GeV 2 < p T,assoc < p T,trig p t,assoc > 2 GeV absolute ridge yield New feature in Au+Au: long range  correlation Persist to high p T,trigger  likely jet-related STAR Preliminary Scenarios:  Parton radiates energy before fragmenting and couples to the longitudinal flow Armesto et al, nucl-ex/0405301  Heating of the medium Chiu & Hwa Phys. Rev. C72:034903,2005 –Radial flow + jet-quenching Voloshin nucl-th/0312065

26. Marco van Leeuwen, High-p T probes at RHIC and LHC 26 RHIC Summary pQCD applicable for p+p at RHIC Strong suppression effects seen for light and heavy flavours Testing radiative energy loss: –Path length dependence confirmed –Heavy flavour suppression stronger than expected –No modifications of away-side shapes in di-hadron correlations Additional dynamics at intermediate p T  medium response Newest results at RHIC start to provide quantitative tests of in-medium energy loss Detailed evaluation ongoing

27. Jets in nuclear collisions at the LHC ATLAS CMS ALICE 2007: p+p collisions @ 14 TeV 2008: Pb+Pb collisions @ 5.5 TeV ALICE is the dedicated Heavy-Ion experiment (high-density tracking and PID) CMS and ATLAS are likely to participate in HI runs as well Complementary capabilities in high-Q 2 probes

28. Marco van Leeuwen, High-p T probes at RHIC and LHC 28 E T jet >100 GeV ~ 10 6 /year Hard process rates at the LHC Annual yields for Pb+Pb at LHC Jet rates and kinematic reach at LHC are huge compared to RHIC High statistics measurements over large kinematic range for precision test of theory

29. Marco van Leeuwen, High-p T probes at RHIC and LHC 29 Inclusive hadron suppression at LHC Initial gluon density at LHC ~ 5-10 x RHIC: Surface bias leads to relatively small change in R AA : Use full jet structure for more differential measurements I. Vitev and M. Gyulassy, PRL 89, 252301(2002) A. Dianese et al., Eur.Phys.J. C38, 461(2005) { First test of jet quenching theory at LHC: Different formalisms give different expectations

30. Marco van Leeuwen, High-p T probes at RHIC and LHC 30 Jet reconstruction at LHC Jet yields at high energies (>50 GeV) are large enough for full jet reconstruction Energy (GeV) Full jet reco removes fragmentation bias  Study jet quenching (modified fragmentation) in more detail Jets accessible over large energy range (50-200 GeV from full jet reco)  Validate jet quenching mechanism And more: –Heavy quark jets –  -jet correlations (calibrate kinematics) –Suprises?  E LHC ≈ 40 GeV  need E T,Jet ~200 GeV for E>>  E 100 GeV jet in central Pb+Pb

31. Marco van Leeuwen, High-p T probes at RHIC and LHC 31 ALICE+EMCal Pb+Pb, 5.5 TeV R jet =0.3 Jet reconstruction in heavy ion events CDF, Phys Rev D65, 092002 (2002) Full jet reconstruction removes fragmentation and geometric biases PYTHIA HERWIG p T charged >5 GeV p T charged >30 GeV 80% Jet cone: CDF: ~80% of jet energy contained in R<0.2 Background from 5.5 TeV Pb+Pb: ~ 75 GeV Use small cone radius ~ 0.3 to suppress backgrounds: Further optimisation of jet-finding parameters awaits data p T -cut for charged hadrons: p T > 2 GeV { With cuts, only modest influence of background fluctuations

32. Marco van Leeuwen, High-p T probes at RHIC and LHC 32 ALICE EMCal Lead-scintillator sampling calorimeter |  |<0.7,  =110 o Shashlik geometry, APD photosensor ~13k towers (  x  ~0.014x0.014) ALICE-EMCal upgrade project in full swing: -First module by 2008 -Full detector by 2009 (Depending on funding) US contribution to ALICE

33. Marco van Leeuwen, High-p T probes at RHIC and LHC 33 MLLA: parton splitting+coherence  angle-ordered parton cascade Good agreement with fragmentation function data  =ln(E Jet /p hadron ) p T hadron ~2 GeV for E jet =100 GeV Fragmentation strongly modified at p T hadron ~1-5 GeV even for the highest energy jets Measuring jet quenching Borghini and Wiedemann Introduce medium effects in parton splitting Use large kinematic reach of LHC to test theory z

34. Marco van Leeuwen, High-p T probes at RHIC and LHC 34 More jet quenching at LHC charm/light Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. Charm and beauty energy loss to distentangle colour charge and mass (dead-cone) effects Z,  -jet to calibrate recoil energy and change geometric bias

35. Marco van Leeuwen, High-p T probes at RHIC and LHC 35 Conclusion pQCD and jet quenching at RHIC reaches quantitative era: –Jet measurements in p+p –Differential measurements of di-hadron fragmentation and suppression –Heavy quark energy loss –Baryon suppression to probe colour charge effects But kinematic reach (‘dynamic range’) is limited Qualitative improvements expected at LHC: -Large kinematic range -Full jet reconstruction

36. Marco van Leeuwen, High-p T probes at RHIC and LHC 36 RHIC outlook Di-hadron correlations in Cu+Cu  -jet correlations  Reducing L with a more penetrating probe Inclusive  -hadron correlations E T,trig > 10 GeV p T,assoc > 4 GeV T. Dietel, QM talk Reducing the coupling to the medium First results available, need differential studies, model comparisons Methods need further development and large data samples

37. Marco van Leeuwen, High-p T probes at RHIC and LHC 37 Extra slides

38. Marco van Leeuwen, High-p T probes at RHIC and LHC 38 Hot and dense QCD matter Phase diagram of nuclear matter Baryon density temperature Hadronic matter (Quasi-)free quarks and gluons Nuclear matter Neutron stars Elementary collisions (accelerator physics) High-density phases? Thermodynamic approachMicroscopic picture Binding force between quarks in protons and neutrons Confinement: isolated quarks cannot exist in vacuum The strong interaction (QCD) Nuclear matterQuark Gluon Plasma High density: large overlap between hadrons  quarks are ‘quasi-free’ Goal: understand dense bulk matter of the Standard Model Early universe RNC research Fundamental phase transition of the Standard Model

39. Marco van Leeuwen, High-p T probes at RHIC and LHC 39 Surface and other bias effects PQM: Dainese, Loizides and Paic X-N Wang, PLB 595, 165 (2004) = STAR preliminary Note also: possible low-z enhancement from fragmentation of induced gluons. Outside measured range, awaits confirmation ‘Surface bias’: - Trigger, associated selection favours short path lengths Surface bias is not the only possibility: -Energy-loss fluctuations (at fixed path length) potentially large -Fragmentation bias Wicks, Horowitz, Djordjevic, Gyulassy nucl-th/0512076 Are we selecting pairs, events with small energy-loss? Alternative: Shape of di-hadron fragmentation changes little if underlying partonic spectrum shape unmodified This calculation underpredicts suppression Partonic spectrum E jet Nuclear geometry L Energy loss  E(E jet ) Fragmentation D(E jet,  E) General form:   Need full calculations, a la PQMDifferent observables probe different parts of convolution