Recent Results from RHIC David Hofman University of Illinois at Chicago EPS 2003 July 17-24, 2003 Aachen

Relativistic Heavy Ions AGS: fixed target, 4.8 GeV/u pair SPS: fixed target, 17 GeV/u pair RHIC: collider, 200 GeV/u pair LHC: collider, 5.4 TeV/u pair RHIC Two concentric superconducting magnet rings, 3.8 km circum. Funded by U.S. Dept. of Energy ($616 million) Construction began Jan. 1991, first collisions June 2000 Au + Au √sNN = (19.6, 56) 130, 200 GeV p + p √sNN = 200 GeV d + Au √sNN = 200 GeV (Just finished spring 2003!) EPS2003 - Aachen

Relativistic Heavy Ions EPS2003 - Aachen

Four Complementary Experiments ~303 collaborators ~307 collaborators Large solid angle tracking ~ Complete events Leptons, (+h’s, g’s) High rate, Sophisticated triggering STAR ~52 collaborators ~68 collaborators ~4p accept. Good vtx. resolution (All Si det.) Tracking & PID at high y EPS2003 - Aachen

Npart/2 = # of participating pairs of nucleons: = 1 p + p Collisions “Participant” Scaling Npart/2 = # of participating pairs of nucleons: = 1 Binary “Collision” Scaling Ncoll = # of NN collisions: = 1 EPS2003 - Aachen

Npart/2 = # of participating pairs of nucleons: ~ A Au+Au Collisions “Participant” Scaling Head-On Collision Npart/2 = # of participating pairs of nucleons: ~ A Binary “Collision” Scaling Head-On Collision A L~A1/3 Ncoll = # of NN collisions: ~ A4/3 EPS2003 - Aachen

Number of Binary Collisions vs. Centrality and Energy Glauber Monte Carlo for Au + Au Collisions sinel=42 mb (RHIC) nmax ~ 6 (RHIC) Au+Au nmax ~ 5 (SPS) n = Ncoll/(Npart/2) sinel=33 mb (SPS) nmax ~ 3 (AGS) sinel=21 mb (AGS) nmax = 1 (p+p) Peripheral collisions Central collisions <Npart> (√sNN=200) ~ 100 EPS2003 - Aachen

Charged Particle Density near Midrapidity EPS2003 - Aachen

Charged Particle Density near Midrapidity Most Naïve Model Possible: A+A = Incoherent Superposition of binary p+p collisions Au+Au Min-bias (n~3.6) (n~3.1) SPS RHIC AGS EPS2003 - Aachen

Charged Particle Density near Midrapidity Central Collisions (for Heavy Ion data) RHIC - combined SPS RHIC AGS EPS2003 - Aachen

Charged Particle Density near Midrapidity Central Collisions (for Heavy Ion data) dN/dyT (for e+e- data) RHIC - combined SPS RHIC AGS EPS2003 - Aachen

RHIC Results for Au + Au Charged Particles mid-rapidity Multiplicities at the very low end of model expectation. (√s = 200 GeV) Energy-density estimates: εBJ ~ 4.6 GeV/fm3 (√s = 130 GeV) (PHENIX; PRL 87 (2001) 052301) εBJ ~ 5.5 GeV/fm3 (√s = 200 GeV) (PHENIX: preliminary) Expectation for a “new form of matter” at energy-densities: ε > 1 GeV/fm3 Mid-Rapidity Density EPS2003 - Aachen

Charged Particle Production at Midrapidity Energy and Centrality Dependence Data is normalized by p+p value for each energy. Binary collision scaling 200 GeV Au+Au 130 GeV 19.6 GeV preliminary Participant scaling p + p Dima, Eugene, Larry peripheral central  Very “flat” particle production with centrality!  Importance of comparing results to proton “baseline”. EPS2003 - Aachen

Suppression in Au+Au Hadron Spectra Binary collision scaling Picture From: T. Peltzmann, QM02 Central collisions at midrapidity BRAHMS STAR PHOBOS h± BRAHMS SEES SAME AT pseudorapidty of 2 h± p0 PHENIX 0-10% Participant scaling  High pT yields in Au+Au are strongly suppressed for central collisions relative to p+p data and collision scaling expectation.  Trend is seen in all four RHIC experiments. EPS2003 - Aachen

Suppression in Au+Au Hadron Spectra STAR: nucl-ex/0305015 0 2 4 6 8 10 12 pT (GeV/c) Saturation: KLM, Phys Lett B561, 93 pQCD: Wang, nucl-th/0305010 (see also Vitev and Gyulassy, PRL 89, 252301) Initial state effect Final state effect EPS2003 - Aachen

p+p jet+jet (STAR@RHIC) Jets at RHIC STAR From: P. Jacobs, RHIC special colloquium Find this… …in this jet p+p jet+jet (STAR@RHIC) Au+Au ??? (STAR@RHIC) parton Select highest pT (>4 GeV/c) “trigger jet” nucleon nucleon → create Df distribution for 2 < pT < pT(trigger) EPS2003 - Aachen

Azimuthal Jet Distributions in Au+Au STAR STAR: PRL 90, 082302 Figs From: P. Jacobs Au+Au peripheral Au+Au central pedestal and flow subtracted pedestal and flow subtracted Near-side: peripheral and central Au+Au similar to p+p Far-side: strong suppression of back-to-back correlations in central Au+Au EPS2003 - Aachen

Suppression: Initial or Final State Effect? Pics From: P. Jacobs Initial state? Final state? partonic energy loss gluon saturation High pT suppression in Au + Au explained by both models. EPS2003 - Aachen

Suppression: Initial or Final State Effect? Pics From: P. Jacobs Initial state? Final state? partonic energy loss gluon saturation High pT suppression in Au + Au explained by both models. How to discriminate? Turn off final state.  d+Au collisions ? EPS2003 - Aachen

Charged Hadron Results @ RHIC d+Au vs. Au+Au at √sNN = 200 GeV STAR d+Au: nucl-ex/0306024 PHENIX d+Au: nucl-ex/0306021 d+Au Au+Au central 0 1 2 3 4 5 6 7 8 9 10 pT (GeV/c) BRAHMS d+Au: nucl-ex/0307003 PHOBOS d+Au: nucl-ex/0306025 pT (GeV/c) 0 2 4 6 0.5 1.0 1.5 2.0 2.5 d+A (0-20%) Au+Au (central) Remind everyone there are subtle differences in Eta space and normalization. d+Au Au+Au central (BRAHMS: same in Au+Au for h=2) pT (GeV/c) EPS2003 - Aachen

p0 Yields Relative to Binary Scaled p+p Color Fig From: T. Hemmick d+Au Binary Collision Scaling Au+Au Also mention PHOBOS centrality dependence. Au+Au: strong suppression d+Au: no suppression EPS2003 - Aachen

Azimuthal Jet Distributions in d+Au STAR Fig From: P. Jacobs pedestal and flow subtracted D f (radians) Near-side: similar result for p+p, d+Au and Au+Au. Far-side: strong suppression of back-to-back correlations only in central Au+Au; NOT in d+Au, p+p nor peripheral Au+Au. EPS2003 - Aachen

RHIC special symposium June 18th 2003 RHIC special symposium Evidence for ‘jet quenching’ in central Au+Au at RHIC Evidence of ‘jet non-quenching’ in d+Au (and peripheral Au+Au) Data suggest we have observed a final state effect produced in a hot dense medium. A few (of many) other hot topics at RHIC: Statistical model and particle ratios – Everything fits with T ~ 176 MeV. HBT Radii – No change in Rside and Rout! Elliptic Flow – Saturates hydrodynamics limit at low pT! – Interesting mass, pT and h dependence! First glimpses of J/Y at RHIC Also mention BRAHMS still sees jet quenching even away from mid-rapidity at Eta ~ 2 EPS2003 - Aachen

Particle Ratios: Fit Beautifully in Statistical Model Fig From: B. Norman Baryochemical potential values (mu_b~45 MeV at 130 GeV and 27 MeV at 200 GeV) assume a chemical freezeout temperature of 165 meV. → Statistical/Thermal model represents data well. → No change in freezeout temperature from 130 to 200 GeV, but decreasing baryon chemical potential. EPS2003 - Aachen

Two pion correlations at RHIC √sNN = 130 GeV Source dimensions by measuring HBT radii. Essentially no change (in Rside and Rout) from AGS (√sNN~4.7) to RHIC (√sNN~200)! Short lived source. Not described in current dynamical models. PHENIX: PRL 88 (2002) 192302 STAR: PRL 87 (2001) 082301 Latest hydro underestimates the size and overestimates the emission time Blast-wave parameterizations give short particle emission time but lifetimes ~ 10 fm/c…not in agreement with recent balance function data. EPS2003 - Aachen

Elliptic Flow: a Collective Effect Initial spatial anisotropy z z Reaction plane (YR) y f x y y x x (defines YR) Final momentum anisotropy dN/d(f -YR ) = N0 (1 + 2v1cos (f-YR) + 2v2cos (2(f-YR)) + ... ) py px Anisotropy parameter v2 EPS2003 - Aachen

RHIC Results Reach Hydro at low pT (PHENIX: nucl-ex/0305013) STAR: nucl-ex/0306007 STAR & PHENIX have similar results for the mass and pT dependence of elliptic flow (v2). Reach hydro limit only at low pT. Different particles deviate from this limit at different values of pT. Mass and pT dependence removed if scale by number of constituent quarks (n). Quark coalescence? → More detailed studies needed. EPS2003 - Aachen

Charged Particle v2 vs. h and Energy PHOBOS: PRL 89, 222301 (2002) Anisotropy parameter v2 Hydrodynamic limit illustration √sNN = 130 GeV (PRL 89) √sNN = 200 GeV (preliminary) Measuring vs. pseuodorapidity is very important to put limits on theory. Hydro matches the charged particle multiplicity. h (pseudorapidity)  Lack of boost invariance. Poses a challenge for theory. EPS2003 - Aachen

J/y from PHENIX The suppression of J/y yields in heavy-ion collisions at SPS is believed to be an important signal for a de-confined state of matter. Important to measure at RHIC. PHENIX has successfully measured J/y at RHIC for p+p collisions. Full story in the next talk! p+p collisions at √s= 200 GeV (In case you forgot: Mass J/y ~ 3.1 GeV) EPS2003 - Aachen

Conclusion: Recent Results from RHIC Clear signatures of high pT suppression (“jet quenching”) in central Au + Au collisions at RHIC that are not present in d + Au. Indication of final state interactions in bulk dense matter. Much more data exists than I had time to show. (Stay in session today and tomorrow for more results.) Many exciting puzzles remain… EPS2003 - Aachen

More RHIC Experimental Talks to Follow J/y production (PHENIX) Nichelle Bruner Charged particle production (PHOBOS) Gerrit van Nieuwenhuizen Freeze-out temperatures and transverse flow (BRAHMS) Oana Ristea Identified Low pT spectra (PHOBOS) Adam Trzupek Identified High pT production (BRAHMS) Zhongbao Yin Charged particle pT spectra (PHOBOS) Rachid Nouicer Strangeness production at RHIC (BRAHMS) Jens I. Jordre EPS2003 - Aachen

Backup Slides

Reminder: Centrality in Au+Au Data Paddle: Multiplicity in 3 < |h| < 4.5 HIJING +GEANT Glauber calculation Model of paddle trigger Peripheral b Central Paddle signal Data+MC Npart EPS2003 - Aachen

Charged Particle Production at Midrapidity Energy and Centrality Dependence PRC 65, 061901(R) (2002); 19.6 GeV in Preparation Midrapidity |h|<1 Au+Au 200 GeV dNch/dh 130 GeV 19.6 GeV preliminary pp two component fit with x~ 0.1 Flat line  See same fraction of about 10% collision scaling fits all energies. EPS2003 - Aachen

Charged Particle Production at Midrapidity Energy and Centrality Dependence Data is normalized by corresponding pp value for each energy. → Data described by model with: 200 GeV 130 GeV Au+Au 19.6 GeV preliminary p + p Dima, Eugene, Larry Kharzeev, Levin, McLerran (KLM) (e.g. PLB 561 (2003) 93)  Initial state (KLM) saturation model also describes full dN/dh shapes; including new effect seen by PHOBOS in the fragmentation region. EPS2003 - Aachen

PT Distribution of Charged Particles “Soft” part of spectrum Phobos Preliminary Systematic Errors not shown  What about high pT? Have a quick look at the “Hard” part of the spectrum. EPS2003 - Aachen

Estimated baryochemical potential at sNN = 200 GeV: B = 26  2 MeV Energy evolution of B Using measured <K–>/<K+>,<p>/<p> and statistical model of F. Becattini et al.,(PRC64,024901,2001) with Tch  160 – 170 MeV Estimated baryochemical potential at sNN = 200 GeV: B = 26  2 MeV LHC ~ 1 MeV? Fit: P.Braun-Munzinger NP. A697,902,2002 EPS2003 - Aachen

Theory Calculations Energy loss applied: M. Gyulassy, I. Vitev, X.N Wang and B.W. Zhang; nucl-th/0302007 dE/dxo is the only free parameter. It is determined by fitting to STAR central RAA(pt) Cronin Effect: X.N. Wang, Phys. Rev C61, 064910 (2000). Attributed to initial state multiple scattering. Implemented by Q2(pt) dependent Gaussian kt broadening EPS2003 - Aachen