Nu Xu RPM, March 23, Recent Results from STAR at RHIC (with focus on bulk properties) Nu Xu Nuclear Science Division

Nu Xu RPM, March 23, P hase diagram of strongly interacting matter CERN-SPS, RHIC, LHC: high temperature, low baryon density AGS, GSI (SIS200): moderate temperature, high baryon density

Nu Xu RPM, March 23, RHIC Au+Au, Cu+Cu, d+Au200 GeVQGP p+p (polarized)200, 500 GeV  g

Nu Xu RPM, March 23, RHIC performance Au+AuL= 8x10 26 cm -2 s -1 at 100GeV/u p+pL= 6x10 31 cm -2 s -1 at 100GeV/u (~70% polarization)L= 8x10 32 cm -2 s -1 at 250GeV/u

Nu Xu RPM, March 23, STAR experiment at RHIC Run Year Species  s NN [GeV ]  Ldt Au+Au  b /2 Au+Au  b -1 p+p pb /3 d+Au nb -1 p+p pb /4 Au+Au  b -1 Au+Au 62 9  b /5 Cu+Cu nb -1 Cu+Cu nb -1 Cu+Cu  b -1 p+p pb -1 The STAR Collaboration: 50 Institutions, ~ 500 People Brazil, China, Croatia, Czech Republic, England, France, Germany, India, Netherlands, Poland, Russia, Switzerland and USA

Nu Xu RPM, March 23, STAR TPC

Nu Xu RPM, March 23, STAR EndCap EMC (1/3) BBC West EMC (Half) Barrel BBC East TPC Detector Configuration EMC Full Barrel 2005 Magnet Full EndCap 2004 Full TOF 2008

Nu Xu RPM, March 23, Au + Au Collisions at 130 GeV STAR Central Event

Nu Xu RPM, March 23, STAR Barrel EMCal

Nu Xu RPM, March 23, High-energy nuclear collisions S. Bass Hadronization and Freeze-out Initial conditions (1)Initial condition in high-energy nuclear collisions - Color Glass Condensate (2)Cold-QCD-matter, small-x, high-parton density - parton structures in nucleon / nucleus Partonic matter - QGP - The hot-QCD Initial high Q 2 interactions (1)Hard scattering production - QCD prediction (2)Interactions with medium - deconfinement/thermalization (3)Initial parton density

Nu Xu RPM, March 23, High-energy nuclear collisions T fo - Thermal freeze-out T ch - Chemical freeze-out T critical - Hadronization =============  Extract EoS prior to hadronization

Nu Xu RPM, March 23, Identify and study the properties of matter with partonic degrees of freedom. Penetrating probes Bulk probes - direct photons, leptons - spectra, v 1, v 2 … - “jets” and heavy flavor - partonic collectivity - fluctuations jets - observed high p T hadrons (at RHIC, p T(min) > 3 GeV/c) collectivity - collective motion of observed hadrons, not necessarily reached thermalization among them. Physics goals at RHIC Hydrodynamic Flow Collectivity Local Thermalization = 

Nu Xu RPM, March 23, Collision Geometry, Flow x z Non-central Collisions Number of participants: number of incoming nucleons in the overlap region Number of binary collisions: number of inelastic nucleon-nucleon collisions Charged particle multiplicity  collision centrality Reaction plane: x-z plane Au + Au  s NN = 200 GeV (|  | < 0.75)

Nu Xu RPM, March 23, Hadron spectra from RHIC p+p and Au+Au collisions at 200 GeV sss ss uud ud

Nu Xu RPM, March 23, Yields ratio results - In central collisions, thermal model fits well with  S = 1. The system is thermalized at RHIC. - Short-lived resonances show deviations. There is life after chemical freeze-out. RHIC white papers , Nucl. Phys. A757, STAR: p102; PHENIX: p184.

Nu Xu RPM, March 23, Energy loss in A+A collisions Nuclear Modification Factor: back-to-back jets disappear leading particle suppressed p+p Au + Au

Nu Xu RPM, March 23, Suppression and Correlation In central Au+Au collisions: hadrons are suppressed and back-to-back ‘jets’ disappear. Different from p+p and d+Au collisions. Energy density at RHIC:  > 5 GeV/fm 3 ~ 30  0 Parton energy loss:Bjorken1982 (“Jet quenching”)Gyulassy & Wang 1992 …

Nu Xu RPM, March 23, Jet-like di-hadron correlations New results, year-4 Larger data sample (year-4) allows analysis at higher p T : -Emergence of the away side peak -Background negligible at higher p T,assoc take from Marco van Leeuwen 8 < p T,trig < 15 GeV

Nu Xu RPM, March 23, Electrons: a mixture c- & b- hadrons M. Djordjevic, et. al. nucl-th/ Partonic energy loss - strongly interacting matter produced at RHIC! Energy loss mechanism: under study M. Gyulassy et al. Problem: isolation of Charm hadron contributions from Beauty-hadrons

Nu Xu RPM, March 23, y x pypy pxpx coordinate-space-anisotropy  momentum-space-anisotropy Anisotropy Parameter v 2 Initial/final conditions, EoS, degrees of freedom

Nu Xu RPM, March 23, v 2 at low p T region - Minimum bias data! At low p T, model result fits mass hierarchy well! - Details do not work, need more flow in the model! P. Huovinen, private communications, 2004

Nu Xu RPM, March 23, Collectivity, Deconfinement at RHIC - v 2, spectra of light hadrons and multi-strange hadrons - scaling of the number of constituent quarks At RHIC, I believe we have achieved:  Partonic Collectivity  Deconfinement PHENIX: PRL91, (03) STAR: PRL92, (04) S. Voloshin, NPA715, 379(03) Models: Greco et al, PRC68, (03) X. Dong, et al., Phys. Lett. B597, 328(04). ….

Nu Xu RPM, March 23, LGT predictions Lattice calculations predict T C ~ 170 MeV 1) Large increase in  a fast cross cover ! 2) Does not reach ideal, non-interaction S. Boltzmann limit !  many body interactions  Collective modes  Quasi-particles are necessary 3) T C ~ 170 MeV robust! Z. Fodor et al, JHEP 0203:014(02) Z. Fodor et al, hep-lat/ C.R. Allton et al, hep-lat/ F. Karsch, Nucl. Phys. A698, 199c(02).

Nu Xu RPM, March 23, “Perfect liquid” at RHIC Kovtun, Son and Strainets, PRL94, (05)Teaney, PRC (03) 1)Experimental data favor hydrodynamic model calculations with small viscosity 2)These results led someone to call the system a “perfect liquid”

Nu Xu RPM, March 23, Late Breaking News November, 2005, Scientific American “The Illusion of Gravity” -- J. Maldacena A test of this prediction comes from the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, which has been colliding gold nuclei at very high energies. A preliminary analysis of these experiments indicates the collisions are creating a fluid with very low viscosity. Even though Son and his co-workers studied a simplified version of chromodynamics, they seem to have come up with a property that is shared by the real world. Does this mean that RHIC is creating small five-dimensional black holes? It is really too early to tell, both experimentally and theoretically.

Nu Xu RPM, March 23, The fate of the Spinosaurid … P.C. Sereno et al. Science, Nov. 13, 1298(1998). (Spinosaurid) For about 50 years Spinosaurid has been vegetarian, now it is a carnivore. For about 20 years, QGP (1980)  sQGP (02)  ‘perfect liquid’ (04) …?

Nu Xu RPM, March 23,  -meson flows STAR Preliminary, QM05 conference S. Blyth et al.

Nu Xu RPM, March 23, hard-soft interactions Two sources of particles: hard: hard scattering products. soft: bulk medium constituents. Very different as seen in peripheral. Become similar in central. from away jets from medium decay Away side (GeV/c) Leading hadrons Medium away near - PID correlation analysis - Search for signal of shock-wave. STAR, nucl-ex/ / PRL 95, (05).

Nu Xu RPM, March 23, In Au + Au collisions: (1) Partonic energy loss - tense interactions amongst partons, strongly interacting matter (2) Partonic collectivity and de-confinement (3) Hadron yields in the state of equilibrium In order to demonstrate the possible early partonic thermalization - QGP, we need to measure heavy flavor collectivity. This is an experimental issue. What we have learned at RHIC

Nu Xu RPM, March 23, Identify and study the properties of matter with partonic degrees of freedom. Penetrating probes Bulk probes - direct photons, leptons - spectra, v 1, v 2 … - “jets” and heavy flavor - partonic collectivity - fluctuations jets - observed high p T hadrons (at RHIC, p T(min) > 3 GeV/c) collectivity - collective motion of observed hadrons, not necessarily reached thermalization among them. Physics goals at RHIC Hydrodynamic Flow Collectivity Local Thermalization = 

Nu Xu RPM, March 23, QCD Energy Scale mCmC m s ~ 0.2 GeV, similar to values T C critical temperature  QCD QCD scale parameter T CH chemical freeze-out temperature   = 4  f  scale for  symmetry breaking m c ~ GeV >>  QCD - pQCD production - parton density at small-x - QCD interaction - medium properties R cc ~ 1/m C => color screening J/  => deconfinement and thermalization u-, d-, s-quarks: light-flavors heavy-flavors c-, b-quarks: heavy-flavors

Nu Xu RPM, March 23, quark mass 1)Higgs mass: electro- weak symmetry breaking. (current quark mass) 2)QCD mass: Chiral symmetry breaking. (constituent quark mass) éStrong interactions do not affect heavy-quark masses.

Nu Xu RPM, March 23, Reconstructed Open Charm Hadrons Measure D o  K  in d + Au and Au + Au for p T < 3 GeV/c Investigating  D ±  K  D0D0 STAR, Phys. Rev. Lett. 94 (2005) H. Zhang (STAR preliminary) QM2005

Nu Xu RPM, March 23, Charm cross sections First set of measurements, systematic errors are large. Precision data are needed: - energy loss analysis  test pQCD in hot and dense medium - J/  analysis  test Charm thermalization and de-confinement

Nu Xu RPM, March 23, Non-photonic electron v 2 Charm flows - a hint for partonic thermalization at RHIC! Problem: Decay effect?

Nu Xu RPM, March 23, Decayed electron p T versus D- and B-hadron p T The correlation between the decayed electrons and heavy-flavor hadrons is weak. Pythia calculation Xin Dong, USTC October 2005

Nu Xu RPM, March 23, Direct Topological Identification of Charm-Hadrons in STAR

Nu Xu RPM, March 23, The Heavy Flavor Tracker 1) A new detector: 30  m silicon pixels to get excellent resolution at the vertex 2) Direct topological reconstruction of Charm hadrons 3) Analyze charm hadron Flow and Energy loss The HFT: 2 layers of Si at mid-y

Nu Xu RPM, March 23, The HFT Mechanical Design Collaboration with LHC Two Layers of Si –1.5 cm radius –5 cm radius High Resolution –100M pixels –30 x 30  m 2 Thin – with low MCS –50  m thinned Si –0.38% radiation length –0.5 mm beam pipe –CMOS APS technology 24 Ladders –10 chips, 2 x 20 cm 2 –100 mW/cm 2 power budget –air cooled end-view side-view

Nu Xu RPM, March 23, Open-charm hadron reconstructions 1) D 0, D s, D +,  c and their anti-particles can be reconstructed with the combination of the HFT+SSD*+TOF+TPC. 2) Decent reconstruction efficiencies at low p T region - important for flow analysis. * Place holder for any adequate intermediate tracking device, such as IST.

Nu Xu RPM, March 23, (1) Test pQCD properties in hot and dense medium - Charm- and bottom-hadron spectra, R AA, charm correlations - Sensitive and detailed study for partonic energy loss  `falsify pQCD, a la Miklos’ - Precision Charm cross section for J/  analysis - direct test de-confinement and Charm thermalization (2) Test light-flavor thermalization - Charm-hadron v 2 - partonic thermalization - Di-lepton invariant mass distributions -  c symmetry Outlook

Nu Xu RPM, March 23, STAR  -vertex Detector J. Thomas, H. Wieman et al., STAR Collaboration