High Energy and Nuclear Physics

1. High Energy and Nuclear Physics Town Meeting at BNL January 21-23, 2001 Diverse group of theorists and experimentalists RHIC Hadron partonic structure Exploit physics commonality among this broad community Presentation today: Heavy Ion Physics - Barbara Spin, p-A physics - Steve Vigdor Barbara V. Jacak Stony Brook March 26, 2001

2. Overarching goal of High Energy Nuclear Physics • Understanding strong interactions at the partonic level • confinement • generation of mass of ordinary matter • quark-gluon structure of h, nuclei • behavior of gluons at high density • QCD: theory underlying the physics • Notoriously hard to solve in strong coupling regime • (most of the interesting cases!) • Synergism: QGP  partonic structure •  initial conditions in RHI •  quantitative calculation of QGP probes •  measurement of QGP properties • Significance: •  mysteries of structure of matter •  cosmological impact •  nuclei: laboratory for the many body problem in QCD

3. Approach • Create high energy density matter • Study confinement, mass generation by inducing transition to QGP • Properties 10 ms after big bang • tool: heavy beams at RHIC • p-p, p-A for baseline physics • Universal behavior of gluonic matter? • many-parton features of QCD in hadrons and nuclei (cold & hot) • sint vs collision energy & gluon density do gluons saturate? Bose condensate? • tool: A-A, p-A, e-A at high energy  highest gluon densities • Resolving power of high energy beams • distribution of pointlike q,g in matter • role of chirality in phase transition and in the hadron properties

4. Achievements: first collisions at RHIC! • Amazing RHIC completion and commisioning • Thanks to TomRoser & BNL team ! Within 6 months: record first collisions commission 4 detectors publish first PRLs Extensive scientific results at Quark Matter conference at Stony Brook in January 2001 I’ll show some of the most exciting ones here

5. with quenching STAR PHENIX BRAHMS No jet quenching Charged particle multiplicity: RHIC enters a new regime! Highest ever! Energy density >50% higher than at CERN PHOBOS PRL85, 3100 (2000) hard scattering important! produces ~ 40% of charged particles hard: scales with Ncoll soft: scales with Npart data begin to distinguish among predictions! nucl-ex/0012008

6. Collective effects?see via elliptic flow Origin: spatial anisotropy of the system when created followed by rescattering of evolving system spatial anisotropy  momentum anisotropy v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane Almond shape overlap region in coordinate space

7. Large v2 at RHIC (as predicted by hydrodynamics) v2= 6%: larger than at CERN or AGS! Hydro. Calculations Huovinen, P. Kolb and U. Heinz STAR PRL 86 (2001) 402 Implies early pressure buildup  therefore early equilibration !? Presence of large collective elliptic flow confirmed by PHOBOS and PHENIX!

8. _ ¯ Central region approaching net baryon-free BRAHMS preliminary antiproton/proton ratio much larger at RHIC  central region dominated by produced pairs, not by initial baryons - antibaryon/baryon - - - - - - STAR preliminary s

9. first hints of jet quenching? • Long predicted new QGP signature • first becoming accessible at RHIC J.C. Dunlop, STAR F. Messer, PHENIX Spectra to pt > 5 GeV/c by PHENIX & STAR p0 Observe a deficit of high pt particles in central collisions  predicted signal of jet quenching in dense matter by Wang, Gyulassy

10. constrain explanations with systematic data • How yields scale with Ncoll or Npart • volume dependence plot as function of pt and Ncoll PHENIX preliminary pt= 0.5 GeV/c soft physics scales as Npart, not Ncoll pt= 3, 4 GeV/c do scale with Ncoll as expected for hard scattering deficit sets in at Ncoll > 300?? (AuAu/collision)/pp NN collisions 103

11. Deficit in both p0 and charged • Identify particles to separate competing processes • Note excess in charged particle spectrum due to baryons - this isnew!

12. Achievements in theory • Color superconductivity and QCD phase diagram • phases at low T and high density • applying BCS & QCD asymptotic freedom • find new phases of QCD matter • understanding initial conditions and small-x gluons • increasing gluon density drives system to weak coupling regime • theoretical techniques, numerical methods for gluon distribution at high density • Quantitative predictions for many observables at RHIC!! • reported at QM00,01 and compiled

13. Computing infrastructure • developed computing infrastructure • successfully handle massive data sets • support analysis by many users • in disparate places • pioneering in scope • not just in nuclear physics, but lead the particle physicists also

14. Compare central Au-Au to p-p • Deficit at high pt seen by both STAR and PHENIX X.N. Wang different from expectation: increase at low pt approach 1 at high pt deficit predicted if quarks lose energy in dense medium (jet quenching)

15. Central Au + Au • p-QCD overestimates the cross-section • for p0 at least a factor of 5 • for charged factor of 2 • misses p &p contribution • shadowing & pt-broadening insufficient • dE/dx = 0.25 GeV/fm consistent with p0 • magnitude & shape differ for charged

16. STAR Radial Flow analysis: mt - slopes versus mass Naïve: T = Tfreeze-out + m  r 2 where  r  = averaged flow velocity • Increased radial flow at RHIC ßr (RHIC) = 0.6c  ßr (SPS/AGS) = 0.4 - 0.5c Tfo (RHIC) = 0.1-0.12 GeV  Tfo (SPS/AGS) = 0.12-0.14 GeV

17. Challenges • What are the properties of QCD at high temperature and density? • Universal behavior of gluonic matter? • Is there evidence for deconfinement? • Correlated onset of predicted signals? • e.g. J/y suppression, s,c enhancement, • jet quenching, fluctuations • will measure this year! • control via p-A, p-p measurements • map collision volume, energy • What is the initial energy density & T? • compare data to lattice QCD predictions • comprehensive theoretical description • Evidence for gluon saturation? • do gluon dynamics dominate the physics? • Restoration of chiral symmetry? • Evidence of in-medium mass changes? • Branching ratio modifications?

18. Challenges, II • What are the initial conditions for heavy ion collisions? • Hard processes (early)  probes • e.g. jets, heavy quarks • Energy loss: interactions in the medium • Bound states: color properties • Hard photons: partonic structure • c,b quarks: gluonic interactions

19. Challenges, III • Does the matter approach thermal equilibrium? • Thermalization & gluon multiplication driven by energy transfer from fast particles? • particle yields & correlations will tell • Thermal radiation: g & dileptons • Momentum & flavor distributions reflect chemical, thermal equilibration • Multiparticle collective observables equilibration early or late (or never?) • What is the equation of state? • How does the hadronic phase evolve? • Hadrons measure dynamics, temperature • Space-time evolution vs. initial conditions • vary volume, temperature • Build coherent theoretical picture constrained by observed initial conditions and final state!

20. International Role • RHIC facility • Unique capability in the world • Flagship facility in the U.S. • LHC in >2006: will explore different physics regime • Strong international participation in experiments • Fraction of collaborators from how many countries • Continue close collaboration pioneered at CERN • Major contributions from Japan • experiment & RHIC hardware • theory • contributions to experiments • Sweden, France, Germany, Russia (in kind), Denmark, Poland, Israel, China, India

21. High Energy Density Theory is truly international • Establishment of RIKEN-BNL Center • Funded by Japan • Led by T.D. Lee • International sponsorship of theory centers • INT (US), ECT* (Europe), • RBRC (Japan) • Many international collaborations and exchanges • Strong collaboration with experimenters

22. Opportunities for U.S. nuclear physicists at LHC • complementary physics regime to RHIC • high density of virtual low-x gluons • should be saturated • time evolution by classical dynamics • high production rate for hard strongly interacting QGP probes • use also weakly interacting probes • W, Z along with g • spatial dependence of saturation & shadowing effects • parton dynamics expected to dominate collective features of collisions • US participation essential • to maintaining our position at frontier of heavy ion research

23. Initiatives for High Energy Nuclear Physics • Run RHIC fully • Detector upgrades • near term • extend kinematic reach • physics coverage • ability of experiments to cross check • fully utilize running time! • major upgrades • open additional physics • charm, low mass lepton pairs • optimize detectors for x40 luminosity • R&D for luminosity upgrade for RHIC • Endorse development of eIC

24. RHIC running time driven by • Low production s probes • high pt hadrons (need >10 GeV/c) • J/y and charmed mesons • multistrange baryons • g-jet and jet-jet coincidences • Need rare processes in energy, beam scans • not just soft physics • p-p and p-A comparisons crucial! • 10 weeks of running at design L • p0 to 20 GeV/c pt • 30K J/ym+m-, 6K J/ y e+e- • 15K e from charm, e-m coincidence • multistrange baryon pt spectra • g-jet correlation sample

25. “Strawman” run plan Impact of shorter runs: scan in energy, volume not possible within 2-3 years (need these for reasonable first conclusions) p-A comparison, open charm measurements compromised

26. Energy scan at RHIC Elliptic and radial flow excitation functions  map out generated pressure H. Appelshauser CERES/QM01 N. Xu STAR/QM01

27. volume scan

28. importance of p-A

29. Luminosity upgrade for RHIC • Physics goals • U spectroscopy, Drell-Yan • W,Z, high ptg • open charm, B yields and distributions • tagged jets • greater kinematic reach • y, Q2, pt • development of electron ring for cooling overlaps with eIC development • R&D in the coming 5 years • accelerator development: electron cooling of ion beams • detector R&D

30. Recommendations I: The RHIC program • Highest priority is full operation of RHIC • Running time recommended by NSAC in 1996 is needed • Statistics for rare processes • Scans in energy, ion size • Polarized p-p • p-A • Support of theory and experiment group operations • Near term upgrades to detectors • Complete utilization of RHIC running • Extend kinematic and physics reach

31. Recommendations II: R&D on accelerator & detector upgrades • To elucidate QCD structure of matter via rare QGP probes at RHIC • increase luminosity by > order of magnitude • pursue R&D toward this goal • Develop high luminosity e-ion collider • R&D on detector technologies • Improve background rejection for charm, dilepton QGP probes • Optimize tracking with high vertex resolution and rate capability

32. Recommendations III: Massively Parallel Computing • Develop multi-teraflop parallel computing facility • For lattice gauge • Other large-scale theoretical problems, • (e.g. hydrodynamics, cascades, Green’s function MC) • Joint effort between BNL, JLAB, FNAL • Aim for 10 teraflop capability • ~ $1.5M per teraflop • apply to DOE Initiative SciDAC • (Scientific Discovery through Advanced Computing)

33. Recommendations IV: Physics at the LHC • in 2006, LHC will provide highest energy HI beams • with dedicated HI experiment (ALICE) • new physics domain • focussed program of U.S. participation • moderate resources • even moderate U.S. effort • ~50 physicists •  significant impact on LHC heavy ion program

34. p-p interpolated for s=130 GeV

35. 250 200 150 100 50 0 Chemical Freeze-out early universe P. Braun-Munzinger, nucl-ex/0007021 LEP/ SppS RHIC quark-gluon plasma SPS AGS Lattice QCD deconfinement chiral restauration Chemical Temperature Tch [MeV] thermal freeze-out SIS hadron gas neutron stars atomic nuclei 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV]