1. 1 Hadronization and chirality in strongly interacting partonic matter: the future of the RHIC Heavy Ion Program Rene Bellwied Wayne State University Nuclear Physics Seminar, Kent State University, Tuesday, March 8 th, 2005

2. 2 A few introductory remarks We found strongly coupled partonic, collective matter (sQGP), which is interesting in itself but it will not secure the future of our field. What defines the relevance of our field in the next two decades ? The QGP paradigm had its time but needs to be updated or replaced. Where do we go from here ? The connection with cosmology is weakening, the connection with QCD is strengthening. The 2007 NSAC Long Range Plan needs to set new goals, especially for the U.S. community.

3. 3 One goal: Proving asymptotic freedom in the laboratory. Measure deconfinement and chiral symmetry restoration under the conditions of maximum particle or energy density. Gross, Politzer, Wilczek win 2004 Nobel Prize in physics for the discovery of asymptotic freedom in the theory of the strong interaction

4. 4 The main features of Quantum Chromodynamics (QCD) Confinement –At large distances the effective coupling between quarks is large, resulting in confinement. –Free quarks are not observed in nature. Asymptotic freedom –At short distances the effective coupling between quarks decreases logarithmically. –Under such conditions quarks and gluons appear to be quasi-free. (Hidden) chiral symmetry –Connected with the quark masses –When confined quarks have a large dynamical mass - constituent mass –In the small coupling limit (some) quarks have small mass - current mass Lattice QCD predicts that deconfinement and chiral symmetry restoration occur at the same critical parameters (T and  )

5. 5 The RHIC-I State Of Affairs: Hydrodynamics describes the bulk Hydrodynamics = strong coupling, small mean free path, lots of interactions not plasma-like Strong collective flow: elliptic and radial expansion with mass ordering requires a partonic EoS

6. 6 For the first time: ideal liquid behavior First time in Heavy-Ion Collisions a system created which, at low p t,is in quantitative agreement with ideal hydrodynamic model. The new phase behaves like an ideal liquid (very low viscosity (D.Teaney)) But are the degrees of freedom partonic ?

7. 7 Confirmed consequences of the sQGP The ‘quenching’ of high pt particles due to radiative partonic energy loss. Energy loss 15 times higher (several GeV/fm 3 ) than in cold nuclear matter (compare STAR AA to HERMES eA) ? The disappearance of the away-side jet in dijet events traversing the opaque medium

8. 8 Constituent quark scaling in the sQGP: Identified particles at intermediate p t Grouping according to number of valence quarks for baryons and mesons, which seem to approach each other around 5 GeV/c coalescence/recombination provides a description ~1.5 - 5 GeV/c constituent quark scaling for hadron production

9. 9 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 Fragmentation ~ 30 GeV/c ? LHC, RHIC-II SPS, RHIC-I RHIC-II: p T to 30 GeV/c

10. 10 Expression of Interest - A Comprehensive New Detector for RHIC II P. Steinberg, T. Ullrich (Brookhaven National Laboratory) M. Calderon (Indiana University) J. Rak (Iowa State University) S. Margetis, C.Markert (Kent State University) M.A. Lisa, D. Magestro, B. Petrak (Ohio State University) R. Lacey (State University of New York, Stony Brook) G. Paic (UNAM Mexico) T. Nayak (VECC Calcutta) R. Bellwied, C. Pruneau, A. Rose, S. Voloshin (Wayne State University) and H. Caines, A. Chikanian, E. Finch, J.W. Harris, M.A.C. Lamont, J. Sandweiss, N. Smirnov (Yale University) (90 pages, submitted in August 2004)

11. 11 The Physics Pillars of R2D What are the detailed properties of the sQGP and what are the degrees of freedom at high densities ? What is the mechanism of hadronization and is chiral symmetry restored in the deconfined medium ? Is there another state (CGC) of matter at low x, what are its features, and how does it evolve into the QGP ? What is the structure and dynamics inside the proton (parton spin, L) and what do we learn from parity violation and polarization measurements ?

12. 12 Evolution of a strongly interacting system Measurements: Initial conditions (  HBT, low-x physics (CGC)) Composition above T c (v2 and jet quenching of partons, constituent quarks, gluonic bound states, pre-hadrons ?) Parton density and chiral symmetry (jet tomography, intra-, inter-jet correlations with resonances) Deconfinement T c (Quarkonium melting) Shuryak QM04 ?

13. 13 In and out of a sQGP What are the degrees of freedom above T C ? Is chiral symmetry restored above T C ? Are chiral symmetry restoration and deconfinement decoupled ? (deconfinement at T C, chiral symmetry restoration well above T C ?). How does hadronization and spontaneous breaking of chiral symmetry (SBCS) occur ? Shuryak QM04 ?

14. 14 How strong is the sQGP ? Lattice QCD :  /T 4 never reaches the Boltzmann limit No perturbative QGP No wQGP Polyakov Loop QCD : Perturbative QGP (wQGP) is reached at 3T c Different initial conditions at RHIC and LHC !

15. 15 The temperature dependent running coupling constant  s A.Peshier et al. (quasi-particles) O.Kaczmarek et al. (thermal mass, LQCD) (hep-ph/0502138) (hep-lat/0406036) 1.05 T c 1.5 T c 3 T c 6 T c 12 T c in an expanding system: interplay between distance and temperature

16. 16 The sQGP degrees of freedom Models that require chiral symmetry breaking above T C : Recombination models: constituent quark (dressed up valence quarks) Models that restore chiral symmetry above T C : Zhe Xu (hep-ph/0406278): multi-gluon interactions (e.g.strong 2 to 3) A. Peshier (Hirschegg 05): quasi particles above T c E.Shuryak (hep-p/0405066): colored and colorless bound states above T c R.Rapp (Hirschegg 05): quasi-resonant heavy states above T C Let’s learn from traditional plasma physics: M. Thoma (hep-ph/0409213): strongly coupled, non-relativistic plasmas Measurements : Elliptic flow v 2 jet quenching High mass resonance shifts due to partonic bound states (Shuryak)

17. 17 What is the relevant scale for QCD ? pQCD Hydro Soft Medium modified fragmentation (jet quenching) 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 Fragmentation pTpT ~ 2 GeV/c~ 6 GeV/c 0~ 30 GeV/c ? LHC, RHIC-II SPS, RHIC-I time t had tftf T(MeV) T had = 170 300 ? T f = 100 400 ? deconfinement Chiral symmetry restoration

18. 18 Recombination is not the only solution for baryon/meson dependence V. Topor-Pop et al. (PRC 70 (2004) 064906) HIJING with: 1.) baryon junction-antijunction loops 2.) pt kick to diquarks 3.) strong color fields Describes: 1.) baryon/meson difference in AA 2.) strangeness yield from pp to AA (incl. multi-strange baryons)

19. 19 Short life time [fm/c] K* <  *<  (1520) <  4 < 6 < 13 < 40 Medium effects on resonances: Mass and width modifications Use resonances with light decay channels, e.g.  to e + e -,  to , a 1 to  Chiral symmetry restoration Measurements: Resonances in jets (Christina Markert, Breckenridge 05) –Is the leading particle resonance different from the bulk matter resonances (off shell vs on shell, same side vs away side, leading vs. next-to-leading) Resonances to prove SBCS (Ralf Rapp, Hirschegg 05) –Is off mass shell resonance (e.g. shifting or broadening in mass) visible in chiral partner pairs (  and a 1 ) or (  and  ) via hadronic channels? Vacuum At T c : Chiral Restoration

20. 20 hadrons leading particle Jet: A localized collection of hadrons which come from a fragmenting parton Parton Distribution Functions Hard-scattering cross-section Fragmentation Function a b c d Parton Distribution Functions Hard-scattering cross-section Fragmentation Function High p T (> 2.0 GeV/c) hadron production in pp collisions: ~ Hadronization in QCD (the factorization theorem) “Collinear factorization”

21. 21  0 in pp: well described by NLO Ingredients (via KKP or Kretzer) –pQCD –Parton distribution functions –Fragmentation functions p+p->  0 + X hep-ex/0305013 S.S. Adler et al.

22. 22 Strange particles in pp This NLO calculation describes K 0 reasonably well, but is off for  B.Jaffe (MIT): maybe we need to look at fragmentation again Universality for FF only shown for pions (KKP 2001)

23. 23 New NLO calculation based on STAR data (AKK, hep-ph/0502188) K0s (V0 vs NLO) apparent E inc dependence. As of now only tested on light mesons

24. 24 Octet baryon fragmentation Bourrely & Soffer (hep-ph/0305070) Strong heavy quark contribution to parton fragmentation into octet baryons at low fractional momentum in pp !! Intrinsic charm in light baryons ?? Fragmentation is not universal !! Is the heavy quark contribution Q-dep.? What is at RHIC ? zz

25. 25 Intrinsic k T, Cronin EffectParton Distribution FunctionsShadowing, EMC Effect Fragmentation Function leading particle suppressed Partonic Energy Loss c d hadrons a b Hard-scattering cross-section High p T Particle Production in A+A

26. 26 Is the fragmentation function modification universal ? Induced Gluon Radiation  ~collinear gluons in cone  “Softened” fragmentation Modification according to Gyulassy et al. (nucl-th/0302077) Quite generic (universal) but attributable to radiative rather than collisional energy loss zz

27. 27 Yu.Dokshitzer Different partons lose different amounts of energy Examples: 1.) dead cone effect for heavy quarks: For heavy quarks in the vacuum and in the medium the radiation at small angles is suppressed (Dokshitzer & Kharzeev, PLB 519 (2001) 199) 2.) gluon vs. quark energy loss: Gluons should lose more energy and have higher particle multiplicities due to the color factor effect.

28. 28 The goal of particle identified fragmentation in the medium 1.) we need to understand fragmentation (hadronization) in pp collisions 2.) use the medium modified fragmentation functions in AA collisions 3.) Different flavor contributions to D(z) at different z lose different  z in the opaque medium. Measure fragmentation functions in pp & modifications in AA. Study z = p hadron /p jet and x dependence : High p T identified particles Intra- and inter-jet particle correlations Large  acceptance for  -tagged jets Essential to understand hadronization 0.2 < z < 1  7 < p < 30 GeV/c 0.1 < x < 0.001  0 <  < 3 p q,g > 10 GeV/c all  10 6 particles in AA

29. 29 The Measurement Pillars of R2D  -jets, g-jets & flavor tagged jets Particle Identification in jet measurements Detailed onium measurements Forward (low x) physics Bulk observables in 4  High rate spin measurements

30. 30 Requirements for a complete jet program Broadening in  and pT in pp (  +jet) and AA Full coverage in tracking and pid and calorimetry Preferably  -jets to determine jet energy unambiguously R2D rates per RHIC year: 40 GeV di-jets: 120k N Ch with pt>5 GeV/c in  -jets with E  = 20 GeV : 19,000 Need hadronic calorimetry in order to apply isolation cuts for  ’s Glueck et al., PRL 73, 388

31. 31 Gluon jet selections at RHIC-II 1.) Large rapidity interval correlations (Mueller-Navelet Jets) 2.) Three jet events (?) 3.) P T -dependence of  -jets (?) low-x gluon 0.001< x g < 0.1 high-x valence quark 0.3 < x q < 0.7

32. 32 Requirements according to RHIC II Physics Pillars  Detailed properties of sQGP (see John’s talk)  Quarkonium: EMC/HCal Resolution, Acceptance, Rates  Jets: PID at high p T and tracking over full acceptance (  -jet, jet-jet)  Mechanisms of hadronization  PID at High p T, correlations, large  acceptance,  -tagged jets  Origin of Spin (of Proton)  Large  acceptance, jets,  -jet, PID at high p T, correlations  Low x physics (CGC  QGP)  PID at high-p T to large   Multi-particle correlations over small & large  range

33. 33 We need high pt PID over large acceptance ! -4-3-2-101234  10 GeV 4 GeV PHENIX STAR, 4 GeV R2D, 25 GeV 0 22 

34. 34

35. 35 A Heavy Ion ‘Dream Detector’: The best of ALICE, CMS and ATLAS combined Prohibitively expensive ?? (requires the utilization of decommissioned HEP detector components (from SLAC, FNAL, DESY)) Present projected price tag: $100 Million Main detector is based on SLD magnet and calorimetry High magnetic field concept Dedicated high momentum detector over full phase space R2D detector concept: best of both worlds

36. 36 Alternative: R2D based on CDF (CDF and CLEO have same field and magnet radius)

37. 37 Do we need RHIC-II in the LHC era ? Is the LHC viewing the sQGP through the distorted lens of the Color Glass Condensate ? (M. Gyulassy) Maybe the QGP degrees of freedom change from RHIC to LHC. Does the sQGP get weaker ? Are we in the sQGP sweet spot ? The conditions will be different. This is a unique situation which allows us to study the QGP from two angles. RHIC-II offers longer running time, higher luminosity, more detailed detector capabilities. LHC offers higher energy and larger cross sections.

38. 38 A few thoughts for your way home The fundamental question of parton to hadron conversion can be tackled through systematic studies of particle identified fragmentation processes inside and outside the produced medium. This is a fundamental question of physics that complements Elementary Particle Physics studies of the Higgs boson ! It will require systematic studies at the LHC and RHIC-II From my point of view that in itself is tantalizing, but it does not lead to a larger physics payoff per se. We have just scratched the surface !! The evidence for QGP formation, i.e. the creation of strongly interacting, collective partonic matter formation is strong (sQGP).

39. 39 The future is bright A three prong approach: lower energy better facility higher energy FAIR: Facility for Antiproton & Ion Reseach LHC: Large Hadron Collider with ALICE, CMS, ATLAS heavy ion programs RHIC-II: RHIC upgrade with new detector R2D critical point (?) hadronization, chirality pQGP (?)