James DunlopHigh p T conference, Finland1 Hard Probes: Past, Present and Future James Dunlop Brookhaven National Laboratory

James DunlopHigh p T conference, Finland2 The Promise of Jet Tomography Simplest way to establish the properties of a system –Calibrated probe –Calibrated interaction –Suppression pattern tells about density profile Heavy ion collisions –Hard processes serve as calibrated probe –Suppression provides density measure + =

James DunlopHigh p T conference, Finland3 Application to Heavy Ion Collisions: Initial Results Strong suppression in Au+Au collisions, no suppresion in d+Au: Effect is due to interactions between the probe and the medium Established use as a probe of the density of the medium Conclusion (at the time): medium is dense (50-100x nuclear matter density) PHENIX: Phys. Rev. Lett. 91 (2003) STAR: Phys. Rev. Lett. 91 (2003) PHOBOS: Phys. Rev. Lett. 91 (2003) BRAHMS: Phys. Rev. Lett. 91 (2003) Binary collision scalingp+p reference

James DunlopHigh p T conference, Finland4 Calibrated Probe: Hard Interactions Hard interactions well understood in perturbative QCD –Factorization holds –PDF (initial) x NLO x FF (final) Example:  0 production well reproduced down to 2 GeV Numerous other examples –   in the forward direction, STAR PRL 92 (2004) 1718 STAR PRL 97 (2006) –proton production in p+p, STAR PLB 637, (2006)161. –Direct  production PHENIX PRD 71 (2005) –Jet production in p+p, STAR PRL 97 (2006) Significant uncertainties in the calculations, so for precision the baseline needs to be measured p+p→  0 +X S.S. Adler et al, Phys. Rev. Lett. 91 (2003) KKP Fragmentation (Data – pQCD)/pQCD

James DunlopHigh p T conference, Finland5 Calibrated Probe? Initial state Initial conditions may not be trivial at forward y at RHIC, at mid-y at the LHC Definitive tests of CGC picture with in run 8 d+Au with the STAR FMS –Wide pseudorapidity range for monojet search (-1 <  < 4, E  up to 60 GeV/c) –Covers x min >10 -3 in standard factorization; reach much lower x in CGC framework First look run 3, STAR PRL 97, (2006).

James DunlopHigh p T conference, Finland6 Central R AA Data Increasing density The Limitations of R AA: “Fragility ” Surface bias leads effectively to saturation of R AA with density Challenge: Increase sensitivity to the density of the medium K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511 A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461

James DunlopHigh p T conference, Finland7 Precision (and its limits) C. Loizides hep-ph/ v2 J. Lajoie [PHENIX] QM2006

James DunlopHigh p T conference, Finland8 Black and White Medium extremely black to hadrons, limiting sensitivity to density Medium transparent to photons (white): no sensitivity Is there something grey? S.S. Adler et al, Phys. Rev. Lett. 94, (2005)

James DunlopHigh p T conference, Finland9 Calibrated Interaction? Grey Probes Problem: interaction with the medium so strong that information lost: “Black” Significant differences between predicted R AA, depending on the probe Experimental possibility: recover sensitivity to the properties of the medium by varying the probe Wicks et al, nucl-ex/

James DunlopHigh p T conference, Finland10 Gluons vs Quarks: Method 1.q jets or g jets  gluon jet contribution to protons is significantly larger than to pions at high p T in p+p collisions at RHIC; pbar/  < 0.1 from quark jet fragmentation at low beam energy. STAR Collaboration, PLB 637, 161 (2006). 2.From Kretzer fragmentation function, the g/q jet contribution is similar to AKK. S. Kretzer, PRD 62, (2000). 200 GeV p+p

James DunlopHigh p T conference, Finland11 Gluons vs. Quarks: Results Gluons should lose more energy than quarks Pions have larger quark contribution than protons SO, Protons should be more suppressed than pions Experimentally NOT observed: equal suppression for p T >6 GeV/c –Perhaps: If medium already black to quarks, can’t be blacker than black Other methods to be tried: kinematics in  (as done in e.g. dijet Sivers) gluon jet quark jet STAR Collaboration, PRL 97 (152301) 2006

James DunlopHigh p T conference, Finland12 Suppression of Charm/Beauty Unexpectedly strong suppression of non-photonic electrons a major issue –Calls into question the calibration of the interaction of the probe with the medium Uncertainties in B contribution: need to measure c and b separately STAR, submitted to PRL, nucl-ex/ PHENIX, submitted to PRL, nucl-ex/

James DunlopHigh p T conference, Finland13 Correlations WMAP: level –One sample –Only photons –Well-defined separation of sources RHIC: to level –Multiple samples –Multiple probes –Model dependence in separation of sources quite a few “two-component” models, with different components

James DunlopHigh p T conference, Finland14 Interpreting Correlations Geometric biases: Hadrons: surface Di-hadrons: tangential, but depending on Eloss can probe deeply Charm-hadron, and especially Beauty-hadron(B): depends on Eloss Note: b and c produced in pairs, B and C decay into multiple hadrons Gamma-hadrons: Precise kinematics, back to surface Beyond reaction of probe to medium, also reaction of medium to probe T. Renk, nucl-ex/

James DunlopHigh p T conference, Finland15 Dijets from dihadrons NOT background subtracted: no ambiguities from background model At high trigger p T, high associated p T : clear jet-like peaks seen on near and away side in central Au+Au 8 < p T (trig) < 15 GeV/c p T (assoc)>6 GeV STAR PRL 97 (2006) d+Au 1/N trig dN/d(  ) Au+Au 20-40%Au+Au 0-5%

James DunlopHigh p T conference, Finland16 Modification of Clean Signals Away-side yield strongly suppressed (almost) to level of R AA No dependence on z T in measured range No modification in shape in transverse or longitudinal direction The jets you can see cleanly are also in some sense the least modified STAR PRL 97 (2006)

James DunlopHigh p T conference, Finland17 Where does the energy go? Lower the associated p T to search for radiated energy Additional energy at low p T BUT no longer collimated into jets Active area: additional handles on the properties of the medium? Mach shocks, Cherenkov cones … e.g. Renk and Ruppert, Phys. Rev. C 73 (2006) PHENIX preliminary Leading hadrons Medium away near M. Horner, QM2006 STAR, Phys. Rev. Lett. 95 (2005) p T (GeV/c) AA/pp STAR preliminary 0-12% 200 GeV Au+Au

James DunlopHigh p T conference, Finland18  -  Correlations Phys. Rev. C73 (2006) mid-central Au+Au p t < 2 GeV d+Au, %Au+Au, 0-5% 3 < p T (trig) < 6 GeV 2 < p T (assoc) < p T (trig) 0.8< p t < 4 GeV STAR PRC 75(2007)  / √  ref In Au+Au: broadening of the near-side correlation in  Seen in multiple analyses –Number correlations at low p T PRC73 (2006) –P T correlations at low p T, for multiple energies Major source of p T fluctuations J. Phys. G 32, L37 (2006) J. Phys. G 34, 451 (2007) –Number correlations at intermediate p T PRC 75, (2007) –Number correlations with trigger particles up to 8 GeV/c D. Magestro, HP2005 J. Putschke, QM2006

James DunlopHigh p T conference, Finland19 Study near-side yields Study away-side correlated yields and shapes Components  near-side jet peak  near-side ridge  v2 modulated background Strategy: Subtract  from  projection: isolate ridge-like correlation Definition of “ridge yield”: ridge yield := Jet+Ridge(  )  Jet(  ) Can also subtract large .     3<p t,trigger <4 GeV p t,assoc. >2 GeV Au+Au 0-10% preliminary  Two-Component Ansatz

James DunlopHigh p T conference, Finland20 The  “Ridge” + “Jet” yield vs Centrality 3<p t,trigger <4 GeV p t,assoc. >2 GeV Au+Au 0-10% preliminary Jet+Ridge (  ) Jet (  ) Jet  ) yield ,  ) N part “Jet” yield constant with N part Jörn Putschke, QM2006 Reminder from p T <2 GeV:  elongated structure already in minbias AuAu  elongation in p-p  to  elongation in AuAu. STAR, PRC 73, (2006) p+p. low p T Number corr elations Au+Au. low p T p T correlations  / √  ref

James DunlopHigh p T conference, Finland21 Extending the ridge: correlations to  =5 Trigger: 3<p T trig <4 GeV/c, A.FTPC: 0.2<p T assoc < 2 GeV/c, A.TPC: 0.2<p T assoc < 3 GeV/c Trigger on mid-  associated particle high  (reverse of FMS) Near-side correlation: consistent with zero (within large v 2 errors) Away-side correlations are very similar (when scaled) Energy loss picture is the same for mid- and forward  ? AuAu 0-10% AuAu 0-5% AuAu 60-80% STAR Preliminary 2.7<|  assoc |<3.9 Levente Molnar, QM2006 STAR Preliminary

James DunlopHigh p T conference, Finland22 STAR preliminary 0-12% 200 GeV Au+Au How to interpret shape modifications? Hard-soft: away-side spectra approaching the bulk. Deflected jets, Mach-cone shock waves, Cherenkov radiation, completely thermalized momentum conservation, or…? Medium away near deflected jets away near Medium mach cone  M. Horner, QM2006 STAR Collaboration, PRL 95, (2005)

James DunlopHigh p T conference, Finland23 Three particle correlations Two Analysis Approaches: Cumulant Method Unambiguous evidence for true three particle correlations. Two-component Jet+Flow-Modulated Background Model Within a model dependent analysis, evidence for conical emission in central Au+Au collisions p T trig =3-4 GeV/c p T assoc =1-2 GeV/c off-diagonal projection d+Au 0-12% Au+Au  =(  1  2 )/2 Δ2Δ2 Δ1Δ1 Δ1Δ1 0-12% Au+Au: jet v 2 =0 Δ2Δ2 C. Pruneau, QM2006 J. Ulery, HP2006 and poster, QM2006

James DunlopHigh p T conference, Finland24 p+p 200 GeV Electron-Hadron Correlations Fit e-h correlation with PYTHIA Ds and Bs Non-zero B contribution Contribution consistent with FONLL –Model dependent (PYTHIA) –Depends mainly on kinematics of D/B decay (not on Fragmentation). Just getting started –e.g. A. Mischke e-D 0 correlations, WW07 Xiaoyan Lin, QM2006

James DunlopHigh p T conference, Finland25 Future at RHIC: “RHIC II” RHIC: luminosity + upgraded detectors for precision –Beauty: last hope for a “grey” probe; needs detector upgrades to both STAR and PHENIX to isolate from charm –  -jet: precision probe of energy loss –Upsilon: precision tests of Debye screening with a “standard candle” Previous Au Run, year 4 STAR HFT PHENIX VTX RHIC

James DunlopHigh p T conference, Finland26 Full Barrel Time-of- Flight system DAQ and TPC-FEE upgrade Forward Meson Spectrom. Integrated Tracking Upgrade HFT pixel detector Inner silicon tracker Forward GEM tracker STAR Upgrades initial state heavy flavor light hadron flow

James DunlopHigh p T conference, Finland27 NCC MPC VTX & FVTX rapidity  coverage 2  HBD EMCAL (i)  0 and direct  with additional EM calorimeters (NCC, MPC) (ii) heavy flavor with silicon vertex tracker (VTX, FVTX) (i)+(ii) for large acceptance  -jet (iii) low mass dileptons (HBD) Upgraded PHENIX Acceptance

James DunlopHigh p T conference, Finland28 STAR Preliminary Golden Probe: Towards  -jet in Au+Au Direct  does not couple to medium or fragment into jets No surface bias on trigger, full kinematics of hard collision But: luminosity hungry, and backgrounds from  0 and fragmentation  STAR QM05, T. Dietel, nucl-ex/ From 30 ub -1 Upgraded RHIC II: 30 nb -1 /year DATA STATISTICS WILL INCREASE BY FACTOR of 1000 in one year at RHIC II

James DunlopHigh p T conference, Finland29 Promising for future  -jet Reminder: spin will measure asymmetries that are ~1% From p+p 2 pb -1, half acceptance Equivalent p+p luminosity in 30 nb -1 Au+Au = 1 fb -1 : factor of 1000 in one year at RHIC II! Use  -enriched sample: plot away-side p T - spectra for photon- tagged events (after subtracting  0 -hadron correlations) Subhasis Chattopadhyay,QM2006 Spectra for DIRECT  -tagged events

James DunlopHigh p T conference, Finland30 Comparison of events/year W.Vogelsang NLO RHIC II L = 20nb-1 LHC: 1 month run  0 suppression at RHIC & LHC NB: large   at RHIC → direct  is ideal probe! Note crossing point at RHIC only STAR & upgraded PHENIX B. Jacak,QM2006

James DunlopHigh p T conference, Finland31 MULTI-particle correlations: events per year: ≥10 GeV  + 2h (p T > p T,min ) Many 3 particle coincidence events (p T >p T,reco )! Full jet reconstruction may be feasible Jet energies lower than LHC… STAR & upgraded PHENIX B. Jacak,QM2006

James DunlopHigh p T conference, Finland GeV: Effects of the Medium Most Apparent energy loss by 20 GeV jets accessible at RHIC (& interpretable) p T trigger > 8 GeV/c STAR PRL nucl-ex/ Majumder, et al. hep-ph/

James DunlopHigh p T conference, Finland33 More Beauty:  signal in p+p Large dataset sampled in Run VI –Only limitation to the trigger is luminosity –Analyzed 5.6 pb -1, with corrections. FACTOR 200x at RHIC II Measure  (1s+2s+3s) d  /dy at y=0 STAR Preliminary p+p 200 GeV e+e- M inv Background Subtracted Pibero Djawotho, QM2006 e+e- M inv Unlike-Sign Pairs — Like-Sign Pairs STAR Preliminary p+p 200 GeV

James DunlopHigh p T conference, Finland34 Mid-rapidity  (1s+2s+3s) Cross section Integrate yield at mid-rapidity: |y|<0.5  (1s+2s+3s) BR * d  /dy –91 ± 28 stat ± 22 syst pb -1 (Preliminary) Consistent with NLO pQCD calculations at midrapidity. Trigger ready for next run and RHIC II: luminosity limited STAR Preliminary p+p 200 GeV Pibero Djawotho, QM2006 y d  /dy (nb) Counts

James DunlopHigh p T conference, Finland35 Annual yields at RHIC II & LHC from Tony Frawley RHIC Users mtg. at LHC: (10-50) x  ~10% of L 25% running time

James DunlopHigh p T conference, Finland36 Separation into Upsilon States At LHC: all 3 states may be suppressed (+coalescence) At RHIC: 1S state clean, likely not suppressed Separation of 2S+3S from 1S challenging, but likely possible –STAR at mid-y –PHENIX with FVTX at forward y Investigating methods to increase capabilities –STAR MTD (muons at mid-y) to remove Bremsstrahlung +HFT+IST for p T resolution RHIC STAR Sim: TPC only Shape analysis p+p vs. Au+Au

James DunlopHigh p T conference, Finland37 Conclusion Jet Quenching well established Moving towards the quantitative –Separate by parton species in search of a grey probe –Track lost energy and its interaction with the medium with two- and multi-particle correlations Watershed in coming years from RHIC II luminosity upgrade and detector upgrades –Precision studies with , b, c, and associated multi-hadron correlations –Complementary, competitive, and in some ways superior, to LHC

James DunlopHigh p T conference, Finland38 p+p Towards  -jet: ( ,  0 )-h  Correlation analysis See Subhasis Chattopadhyay, QM2006 Use “shower-shapes” in EMC: Create two samples Enriched photon sample (mix ,  0 ) Enriched  0 sample (almost pure  0 ) Reduction in near angle peak in Photon sample Away-side yields only slightly reduced Effect more prominent for larger Et trigger  0 Mixed Photon From p+p collisions run 5, 2 pb -1

James DunlopHigh p T conference, Finland39 Away-Side: p T trig Dependence 0-12% 1.3 < p T assoc < 1.8 GeV/c 4.0 < p T trig < 6.0 GeV/c 6.0 < p T trig < 10.0 GeV/c Away-side: –Structures depend on range of p T. –becomes flatter with increasing p T trig –yield increases 3.0 < p T trig < 4.0 GeV/c AuAu 0-12% Central contribution to away-side becomes more significant with harder p T trig => fills dip Preliminary Away side Mark Horner, QM2006

James DunlopHigh p T conference, Finland40 Calibrated Interaction: Radiative energy loss in dense matter Multiple soft interactions: Strong dependence of energy loss on gluon density  glue  measure   color charge density at early hot, dense phase Gluon bremsstrahlung Opacity expansion: Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,… Other formalisms since then, but all agree that the relevant parameter is the density