1 Particle production mechanisms from RHIC to LHC Rene Bellwied Wayne State University International Workshop on High pT Physics at the LHC, Jyvaskyla, Finland March 23 rd -27 th,2007

2 The Quark Soup – when does it vaporize ? liquid ? liquid plasma gas Hirano, Gyulassy (2006)

3 The Quark Soup – when does it vaporize ? liquid ? liquid plasma gas wQGP ? sQGP ? RHIC LHC ? 1.) is there a wQGP at the LHC ? 2.) is chiral symmetry decoupled from deconfinement in the sQGP ? 3.) are the degrees of freedom different in the sQGP and the wQGP ? 4.) does it matter if the partonic medium always de-excites through the quark soup phase ?

4 Chiral and deconfinement transitions still happen at the same temperature Interlude: news from Lattice QCD (Peter Petreczky, Big Sky, Feb.2007) Critical Temp T c = MeV At high T deviation from ideal gas limit is only about 10%

5 SU(3) gauge theory (2+1) flavor QCD Resummed perturbative calculations from : Blaizot, Iancu, Rebhan, hep-ph/ Lattice data on pressure and entropy density at high temperatures can be described by re-summed perturbation theory Is 10% a large effect ? Comparison with re-summed perturbation theory, effective 3d theory and additional lattice data on quark number susceptibility and the Debye mass suggest that we have wQGP for T > 2 T c

6 So what do we know about the sQGP degrees of freedom at RHIC Elliptic flow and radiative energy loss seems to be sensitive to the partonic degrees of freedom There is little evidence for chiral symmetry restoration in resonance and vector meson studies There is ample evidence for deconfinement in v2, energy loss and quarkonia studies.

7 The medium consists of constituent quarks ? baryons mesons

8 At higher pt: all particle v2 follows NCQ scaling STAR preliminary

9 Nuclear Modification Factor R cp 0-5% 40-60% 0-5% 60-80% √s NN =200 GeV Baryon and meson suppression sets in at the same quark p T. √s NN =200 GeV Strange R CP signals range of recombination model relevance Recombination scaling can be applied to R CP as well as v2

10 Sea-quarks and gluons in recombination (higher Fock states admixture in thermal sudden recombination) Effects of sea-quarks and gluons on v2 measurement are small

11 Contributions to particle production in RHI collisions pTpT pQCD Hydro ~ 2 GeV/c~ 6 GeV/c Soft Medium modified fragmentation (jet quenching) 0 p T independence of pbar/p ratio. p/  and  /K ratio increases with p T to > 1 at p T ~ 3-4 GeV/c in central collisions. Suppression factors of p,  different to that of , K 0 s in the intermediate p T region. Parton recombination and coalescence LHC, RHIC-II SPS, RHIC-I Thermal

12 Particle production in jet distinctly different than in medium Associated particle production (B/M ratio) similar in ridge and medium and about a factor 2-3 different than in the jet. Ridge and medium have similar production mechanism ? Recombination ?  /K~1  /K~0.5

13 STAR preliminary Do the pT dependencies in the recombination results hint at a more ‘massive’ strange quark ? Light & strange baryon to meson ratios

14 Flavor dependence of yield scaling participant scaling for light quark hadrons (soft production) binary scaling for heavy flavor quark hadrons (hard production) strangeness is not well understood (canonical suppression in pp) PHENIX D-mesons up, down strange charm

15 s-quarks are formed primordial Scaling according to quark content? u, d – scale with N part s,c,b – scale with N bin p – N part K 0 s – 1/2*N part + 1/2*N bin  – 2/3*N part + 1/3*N bin  – 1/3*N part + 2/3*N bin  – N bin  – N bin D – N bin Primordially produced strange quarks have to recombine with ‘thermal’ u,d quarks (thermal-shower picture ?) Normalized to central data

16 The fate of strangeness enhancement at the LHC Canonical suppression in pp should reduce as a function of the incident energy The absolute yield rises but only linear with the yield of pions in a QGP The integrated yield is predictable, the pt-differential yield holds the new physics Hypothesis: due to the higher energy, the remaining differences between u,d and s quarks should significantly reduce (no Nbin scaling, same d.o.f.)

17 Interlude: what do we know right now ? The degree of freedom for light quark particles seems to be a constituent quark (or a quasi-particle..). It is not massless in the strictest sense, but the ‘mass’ is the same for u,d,s quarks. Deconfinement, not necessarily chiral symmetry restoration These degrees of freedom seem to recombine in partonic medium to form hadrons. This is distinctly different from jet fragmentation. The strange quark seems to be produced primordially, whereas the light quarks a largely ‘thermal’. Effect should reduce at LHC, if hadronization occurs at same T (canonical suppression melts away (R. Stock)) Interesting test: the charm with a bare quark mass of 1300 MeV. It is definitely produced primordially but it also has a larger ‘thermal’ or ‘interaction’ mass. In other words it is a heavier quasi-particle.

18 χ 2 minimum result D->e 2σ 4σ 1σ A.) charm flows like light quarks strong elliptic flow of electrons from D meson decays → v 2 D > 0 v 2 c of charm quarks? recombination Ansatz: (Lin & Molnar, PRC 68 (2003) ) universal v 2 (p T ) for all quarks simultaneous fit to , K, e v 2 (p T ) a = 1 b = 0.96  2 /ndf: 22/27

19 submitted to PRL (nucl-ex/ ) charged hadrons B.) charm quenches like light quarks Describing the suppression is difficult for models radiative energy loss with typical gluon densities is not enough (Djordjevic et al., PLB 632(2006)81) models involving a very opaque medium agree better (qhat very high !!) (Armesto et al., PLB 637(2006)362) collisional energy loss / resonant elastic scattering (Wicks et al., nucl-th/ , van Hees & Rapp, PRC 73(2006)034913)

20 Useful to constrain medium viscosity  /s…. Simultaneous description of STAR & PHENIX R(AA) and PHENIX v2for charm. (Rapp & Van Hees, PRC 71, 2005) Ads/CFT ==  /s ~ 1/4  ~ 0.08 Perturbative calculation of D (2  t) ~6 (Teaney & Moore, PRC 71, 2005) ==  /s~1 transport models require –small heavy quark relaxation time –small diffusion coefficient D HQ x (2  T) ~ 4-6 –this value constrains the ratio viscosity/entropy  /s ~ (1.3 – 2) / 4  within a factor 2 of conjectured lower quantum bound consistent with light hadron v 2 analysis electron R AA ~  0 R AA at high p T - is bottom suppressed as well? …but what does it mean for the partonic degrees of freedom ?

21 Heavy q-qbar bound states (resonances) can survive in lattice QCD up to 2 Tc. This is not a quasi-particle or a constituent quark but a surviving heavy quark bound state Same v2 and R(AA) but different cause… [Rapp & van Hees, hep-ph/ ] Nuclear Modification Factor resonance effects large bottom much less affected characteristic “leveling-off” factor 3-4 from resonances Elliptic Flow

22 So charm looks like light quarks but the degrees of freedom are different Funny coincidence ? Is this theory verifiable, is there a distinguishing feature ? Energy dependence should show effects –A.) at lower energies qbar and gluon more suppressed, D+ vs. D- differences in v2 and R(AA) –B.) secondary production of heavy quarks is suppressed at RHIC Heavy quark at RHIC is very sensitive to recombination Strong partonic recombination to quarkonia at LHC –C.) bound states only survive up to 2 Tc. No bound state survival in initial phase at LHC

23 There are alternatives.. Interesting formation time argument by I. Vitev (hep-ph/ ) Based on: a.) fragmentation probability for heavy quarks b.)medium-induced decay probability for heavy hadrons, i.e. collisional dissociation probability of heavy hadrons in QGP size of system L T QGP < 6 fm at p T = 10 GeV/c:  form (  ) ~25 fm  form (D,B) ~ 1.6, 0.4 fm Interesting: predicts suppression of B-mesons out to 10 GeV/c

24 Formation time argument for chiral symmetry restoration evidence (C. Markert, STAR, in progress) side 1 side 2 near away Low ptHigh pt Near sideNo medium or late hadronic medium No medium Away side Late hadronic mediumPartonic or early hadronic medium (depend on formation time) Side 1&2Late hadonic mediumEarly hadronic medium K. Gallmeister, T. Falter. Phys.Lett.B630:40-48,2005 General pQCD: Formation time [fm/c] ~ p T [GeV] Specific string fragmentation (PYTHIA) formalism: Gallmeister, Falter, PLB630, 40 (2005) Heavier particles form later, Resonances form earlier

25 Any major changes at the LHC ? (besides less coupling and less ‘dressed up’ valence quarks)

26 Hydro pushes to higher pT at the LHC Ruuskanen et al., hep-ph/ but v2 might reduce because early phase of QGP is more weakly coupled (RB for the R2D group, QM05)

27 Recombination pushes to higher pT at the LHC Thermal recombination pushes to higher pT (~2-10 GeV/c ?) because of higher parton Shower recombination (from overlapping or neighboring jets) pushes recombination out to 20 GeV/c (Hwa, nucl-th/ )

28 Jet quenching will populate the recombination region at the LHC Borghini and Wiedemann (hep-ph/ ): solid lines: modified leading logarithm approximation (MLLA) dashed lines: introduce medium effects in parton splitting  =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

29 It will be challenging to interpret the intermediate pT region at the LHC pTpT pQCD Hydro ~ 2 GeV/c~ 6 GeV/c Soft Medium modified fragmentation (jet quenching) 0 p T independence of pbar/p ratio. p/  and  /K ratio increases with p T to > 1 at p T ~ 3-4 GeV/c in central collisions. Suppression factors of p,  different to that of , K 0 s in the intermediate p T region. Parton recombination and coalescence LHC, RHIC-II SPS, RHIC-I Thermal

30 Summary – Questions for the LHC We have more evidence for constituent quark scaling above T c. Is recombination the dominating hadronization process at RHIC and LHC energies ? Do the hadronizing degrees of freedom in the Quark Gluon Liquid have a dynamic mass ? Could there be a decoupling of the deconfinement transition and chiral symmetry restoration ? Is there another transition from the sQGP to the wQGP at LHC energies ? The excitation function (energy dependence) of v2 and R(AA) of identified particles will resolve many of the present ambiguities

31 Weinberg’s 3 rd law of Theoretical Physics You may use any degrees of freedom you like to describe a physical system, but if you use the wrong ones, you’ll be sorry ! Lattice QCD based dynamic QCD vacuum visualization, Adelaide Group