Ralf Averbeck State University of New York at Stony Brook Quark Matter 2004, Oakland January , 2004 Leptons, Photons, and Heavy Quarks

R. Averbeck, SUNY Stony Brook 2 l Low and Intermediate-Mass Dileptons l open questions l pending answers l Direct Photons l controlling jets l Heavy Flavor l charmonia –news from SPS –preparing the case for RHIC l open charm at RHIC –reference and probe l Summary Outline

R. Averbeck, SUNY Stony Brook 3 l origin of intermediate-mass dimuons l dimuon excess observed at intermediate masses (NA50) –charm enhancement? –thermal dimuons? the  puzzle discrepancy between NA49  K + K - ) and NA50      physics (  in-medium vs.  at freeze-out)? SPS dilepton experiments: open questions l low-mass dielectrons l excess established by NA45/CERES vector mesons, i.e.  ? –where are they? –medium modifications of yield, mass, width?

R. Averbeck, SUNY Stony Brook 4 SPS dilepton experiments: answers? SPS dilepton experiments: perspectives! l NA45/CERES (talks by A. Marin, A. Cherlin) l improved mass resolution (TPC) possibility for  e + e - and  K + K - in one experiment l work in progress   5000 signal events for M < 1.2 GeV (less than 1 % of total statistics) peripheral: N ch < 40 l NA60 (talks by P. Sonderegger, A. David) l DESIGNED to answer open questions! –high statistics due to selective trigger –good mass resolution (~20 MeV for  ) –good phase-space coverage (down to zero p T ) –50  m secondary vertex resolution (prompt  vs.  from charm decays) l Indium+Indium at 158 AGeV (2003) –>10 6 low-mass dimuons! –S/B: ½ - 1 (depending on centrality) –>10 5      K + K - feasible as well l proton reference run forthcoming (2004) NOT YET!

R. Averbeck, SUNY Stony Brook 5 Low-mass dileptons at RHIC l PHENIX (talk by R. Seto): resonance measurements in leptonic and hadronic channels in ONE experiment l look forward to results from large statistics Au+Au Run04 at RHIC  l continuum (low and intermediate mass) l RHIC upgrades (talk by A. Drees): l electron identification  Dalitz / Conversion rejection (poster by I. Ravinovich) l Silicon vertex spectrometers  resolve secondary vertices (heavy flavor physics) M T (GeV/c 2 ) e+e-e+e-  s NN = 200 GeV Minimum bias d+Au 1/2  m T dN/dm T dy (GeV/c 2 ) -2 K+K-K+K- dN/dy PHENIX Preliminary l posters by C. Maguire, D. Pal, Y. Tsuchimoto

R. Averbeck, SUNY Stony Brook 6 Virtual photons  real photons l real photon sources in AA collisions l “trivial”  background –decays of light hadrons (    ) –dominant at low / intermediate p T (few GeV/c) l “thermal”  black body radiation from hot medium –partonic and/or hadronic medium –expected at low p T on top of huge background l “direct”  photons from initial state hard scattering –Compton scattering dominates, i.e. probe for gluon distribution –calculable in pQCD –no fragmentation of photon! –photon “shines through” hot and dense medium! l direct photons “calibrate” hard scattering processes  IDEAL CONTROL EXPERIMENT FOR JET SUPPRESSION! l how-to measure direct photons l subtraction of “background” photons (WA98 / PHENIX) l photon correlations (WA98 talk by D. Peressounko) Subtraction method, upper limit Correlation method: Subtraction method Predictions hadronic gas QGP sum pQCD Most probable yield (R o =6 fm) The lowest yield (R o =0)

R. Averbeck, SUNY Stony Brook 7 Ratio PHENIX Preliminary Direct photons from 200 GeV pp collisions   PHENIX Preliminary   expected bkg   measured l evaluation of excess above background: double ratio [  ] measured / [  background   measured /  background l (small) direct photon signal observed! (PHENIX talk by J. Frantz, posters by G. David, K. Reygers, T. Sakaguchi ) PHENIX Preliminary Vogelsang NLO l consistent with NLO pQCD calculation (W. Vogelsang: JHEP 9903 (1999) 025 & priv. comm.)

R. Averbeck, SUNY Stony Brook 8 PHENIX Preliminary PbGl / PbSc Combined AuAu 200 GeV Central 0-10% (large new p T region) Direct photons from 200 GeV AuAu collisions l strong suppression of high p T pions in central AuAu collisions l VERY significant background reduction!

R. Averbeck, SUNY Stony Brook 9 Comparison with NLO pQCD calculation l nice agreement with unsuppressed, binary scaled pp NLO pQCD calculation! 1 + (  pQCD direct x N coll ) / (  phenix pp backgrd x N coll ) 1 + (  pQCD direct x N coll ) /  phenix backgrd Vogelsang NLO 1 + (  pQCD direct x N coll ) /  phenix backgrd Vogelsang, m scale = 0.5, 2.0 PHENIX Preliminary PbGl / PbSc Combined AuAu 200 GeV Central 0-10%

R. Averbeck, SUNY Stony Brook % Central AuAu 200 GeV PHENIX Preliminary PbGl / PbSc Combined 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang NLO 70-80% Central AuAu 200 GeV PHENIX Preliminary PbGl / PbSc Combined 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang NLO 60-70% Central AuAu 200 GeV PHENIX Preliminary PbGl / PbSc Combined 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang NLO 50-60% Central AuAu 200 GeV PHENIX Preliminary PbGl / PbSc Combined 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang NLO 40-50% Central AuAu 200 GeV PHENIX Preliminary PbGl / PbSc Combined 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang NLO 30-40% Central AuAu 200 GeV PHENIX Preliminary PbGl / PbSc Combined 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang NLO 20-30% Central AuAu 200 GeV PHENIX Preliminary PbGl / PbSc Combined 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang NLO 10-20% Central 200 GeV AuAu PHENIX Preliminary PbGl / PbSc 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang 0-10% Central 200 GeV AuAu PHENIX Preliminary PbGl / PbSc Combined 1 + (  pQCD x N coll ) /  phenix backgrd Vogelsang NLO Direct photons: centrality dependence l direct photons are not inhibited by hot/dense medium and shine through consistent with pQCD! l thermal photons: reduction of systematic uncertainties is essential!!

R. Averbeck, SUNY Stony Brook 11 Another hard probe: heavy flavor production l a (very) complex playground l cc production in hard scattering –sensitive to PDF l propagation l hadronization l medium modifications l modification of PDF in nuclei (shadowing, antishadowing) l multiple scattering  p T broadening l initial state parton energy loss l charmonia: –“normal” nuclear absorption –“anomalous” suppression (“Debye” screening) –enhancement via “coalescence”? l additional “thermal” production? l energy loss by induced gluon radiation? “Dead-cone effect”? l …. D mesons,  ’,  l how to disentangle this? l measure charmonium states and open charm l in pp, pA, AA collisions l in various kinematic regions l at various energies –news from SPS –news from RHIC

R. Averbeck, SUNY Stony Brook 12 J/  suppression in PbPb at SPS updated analysis of J/  (and  ’) absorption in cold nuclear matter (NA50 pA run at 400 GeV (2000) + combined fit of ALL data sets) (NA50 talk by G. Borges)  J/  abs = 4.3 ± 0.3 mb J/  suppression with respect to this expected “normal” nuclear absorption (relative to Drell-Yan): a familiar pattern l what is new?  ’ measurement l challenging because of –small dimuon cross section –small S/B –large suppression (weaker bound state than J/  )

R. Averbeck, SUNY Stony Brook 13  ’ suppression at SPS  ’ suppression relative to Drell-Yan and J/  increases with centrality in PbPb collisions  talk by H. Santos  ’ absorption in pA is stronger than J/  absorption l significantly stronger absorption in AA going from peripheral to central collisions l no apparent difference in absorption pattern between SU and PbPb collisions

R. Averbeck, SUNY Stony Brook 14 Open questions at SPS what fraction of J/  comes from  c feed down (  c  J/  +  )? what is the nuclear dependence of  c production/absorption in pA? l is open charm enhanced in AA?  c measurement at HERA-B (huge statistics dilepton data sample from pA collisions at  s NN = 42 GeV) (HERA-B talks by J. Spengler, A. Gorisek) lwill be answered by NA60  c /J/  from 15 % of available statistics  m  -m J/ 

R. Averbeck, SUNY Stony Brook 15 J/  suppression / enhancement at RHIC? l PHENIX: preparing the case YearIons  s NN Detectors J/  2000Au-Au130 GeV Central (electrons) Au-Au200 GeV Central p-p200 GeV + 1 muon arm d-Au200 GeV Central p-p200 GeV + 2 muon arms Au-Au200 GeV! ready !~400+2x1600 ? QM2002 first observation QM2004 first sizeable pp & dAu samples study J/  modifications in cold nuclear medium

R. Averbeck, SUNY Stony Brook 16 Predicted Gluon Shadowing in d+Au J/  in dAu collisions at RHIC l J/  produced by gluon fusion l sensitivity to gluon pdf l 3 rapidity ranges in PHENIX probe different momentum fraction of Au partons l South (y < -1.2) : large X 2 (in gold) l Central (y ~ 0) : intermediate l North (y > 1.2) : small X 2 (in gold) From Eskola, Kolhinen, Vogt Nucl. Phys. A696 (2001) X1X1 X2X2 J/  in North y > 0 X1X1 X2X2 J/  in South y < 0 rapidity y Au d

R. Averbeck, SUNY Stony Brook 17 Au d J/  in pp and dAu collisions at RHIC l rapidity distributions: improved pp / first dAu measurements l PHENIX talk by R. G. de Cassagnac, posters: J.M. Burward-Hoy, S. Kametani, D. Kim, D. Silvermyr

R. Averbeck, SUNY Stony Brook 18 J/  dAu/pp versus rapidity at RHIC S.B. Klein and R. Vogt, nucl-th/ Low x 2 (shadowing) l indication for (weak) shadowing and absorption l centrality dependence studied as well! l more statistics desirable to disentangle nuclear effects (and distinguish models) Au d High x 2 Low x 2 STAGE IS SET Look forward to high statistics AuAu run!

R. Averbeck, SUNY Stony Brook 19 Open charm: reference and probe l physics motivation for open charm measurements reference for J/  suppression / enhancement l production mainly via gluon fusion  interesting probe itself –sensitive to gluon structure function (and nuclear modification of this) – heavy quark energy loss –induced gluon radiation –“dead cone” effect –does charm flow? l open charm measurements at RHIC K-K- e+e+ e  K+K+ -- D *0  D0D0 c direct reconstruction ideal, difficult in HI, doable 200 GeV dAu: STAR (mb) indirect measurements electrons from semileptonic decays 130 GeV AuAu: PHENIX (cent.) 200 GeV pp: PHENIX & STAR 200 GeV dAu: PHENIX (cent.) & STAR (mb) 200 GeV AuAu: PHENIX (cent)

R. Averbeck, SUNY Stony Brook 20 First direct charm measurement (STAR) l reconstruction of D mesons in minimum bias dAu collisions l D 0 l D ± l D * D 0 +D 0 0 < p T < 3 GeV/c, |y| < 1.0 d+Au minbias = 1.12 ± 0.20 ± 0.37 mb from D data (1.36 ± 0.20 ± 0.39 mb with electrons) l STAR talks by A. Tai, L. Ruan, A. Suaide

R. Averbeck, SUNY Stony Brook 21 Open charm in pp: the baseline l two single electron measurements l three methods to subtract photonic background (PHENIX talk by S. Kelly) l three methods to identify electrons (STAR talk by A. Suaide) p + p d + Au PHENIX PRELIMINARY l charm cross sections (barely) agree! =1.36 ± 0.20 ± 0.39 mb

R. Averbeck, SUNY Stony Brook 22 Consistency between electron data sets l STAR systematically (slightly) above PHENIX l beware: error bars are meant to be taken seriously!

R. Averbeck, SUNY Stony Brook 23 Does the PYTHIA extrapolation work? l PYTHIA tuned to available data (  s NN < 63 GeV) BEFORE RHIC results PHENIX PRELIMINARY l spectra are harder than PYTHIA extrapolation from low energies! (hard fragmentation function, charm quark recombination …?) l PYTHIA can’t be used to extract bottom cross section! l bottom measurement requires PRECICE D measurement first!

R. Averbeck, SUNY Stony Brook 24 Centrality dependence in dAu (PHENIX) l single electrons from non-photonic sources agree well with pp fit and binary scaling (posters: S. Butsyk, X. Li) PHENIX PRELIMINARY 1/T AB EdN/dp 3 [mb GeV -2 ] PHENIX PRELIMINARY 1/T AB 1/T AB EdN/dp 3 [mb GeV -2 ]

R. Averbeck, SUNY Stony Brook 25 1/T AA Centrality dependence in AuAu (PHENIX) l uncertainties too large for definite statements regarding (small) deviations from binary scaled pp results (poster: T. Hachiya) 1/T AA 1/T AB EdN/dp 3 [mb GeV -2 ]

R. Averbeck, SUNY Stony Brook 26 Binary collision scaling in AuAu (PHENIX) <  < dN/dy = A (N coll )  l binary collision scaling of pp result works VERY WELL for non-photonic electrons in AuAu (PHENIX talk by S. Kelly) l open charm is a good CONTROL, similar to direct photons!

R. Averbeck, SUNY Stony Brook 27 Does charm flow? PHENIX PRELIMINARY l is partonic flow realized? l v2 of non-photonic electrons indicates non-zero charm flow in AuAu collisions l uncertainties are large l definite answer: AuAu RUN-04 at RHIC! l PHENIX poster by S. Sakai

R. Averbeck, SUNY Stony Brook 28 Summary l low and intermediate-mass dileptons l looking forward to –solutions of SPS puzzles –data from RHIC l direct photons as jet control measurement l pQCD at work l charmonia l improvements at SPS l preparing the reference for RHIC l open charm l a second player joined the game l what next? l LUMINOSITY!! l back to work