PHOBOS Collaboration

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Published on June 15, 2007

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Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC:  for the Collaboration Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC Adam Trzupek The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences Kraków, Poland 4th Budapest Winter School on Heavy Ion Collisions (December 1st-3rd 2004) in Budapest, Hungary nucl-ex/0410022, 2004 PHOBOS Collaboration:  Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Backer, Russell Betts, Abigail Bickley, Richard Bindel, Andrzej Budzanowski,Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Steve Gashue, Clive Halliwell, Joshua Hamblen, Adam Harington, Michael Hauer, George Heintzelman, Conor Henderson, David Hofman, Richard Hollis, Roman Holynski, Burt Holzman, Aneta Iordanova, Erik Johnson, Jay Kane, Judith Katzy, Nazim Khan, Wojtek Kucewicz, Piotr Kulinich, Chia Ming Kuo, Jang Wo Lee, Willis Lin, Steven Manly, Don McLeod, Alice Mignerey, Rachid Nouicer , Gerrit van Nieuwenhuizen, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Mike Reuter, Christof Roland, Gunther Roland, Leslie Rosenberg, Joe Sagerer, Pradeep Sarin, Paweł Sawicki, Helen Seals, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Jaw-Luen Tang, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch, Jinlong Zhang ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKÓW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER PHOBOS Collaboration Slide3:  PHOBOS Detector T0 counter Spectrometer SpecTOF TOF multiplicity, vertex and calorimeter detectors are not labeled (see Russell Betts talk) Magnet Paddle Trigger counter Paddle Trigger counter T0 counter pT and PID Measurement in PHOBOS Spectrometer:  pT = 0.2 - ~5 GeV/c track curvature in B field =andgt; p,charge dE/dx in Si, ToF =andgt; mass pT = 0.03 - 0.2 GeV/c low-p particles stop in silicon wafers =andgt; p, mass B field negligible =andgt; no charge identification pT and PID Measurement in PHOBOS Spectrometer 10 cm PHOBOS Spectrometer dipole magnetic field of 2T at maximum 16 layers of silicon wafers fine/optimal pixelization, precise dE measurement collision vertex close to spectrometer near mid-rapidity coverage 70 cm PID Measurement in PHOBOS Spectrometer:  PID Measurement in PHOBOS Spectrometer andlt;dE/dxandgt; pT andgt; 0.2 GeV/c pT = 0.03 - 0.2 GeV/c Etot =  dEi , i=A, ... ,E Mpi = Ei dEi/dx Mp = andlt; Mpi andgt; /K separation: pT andlt; ~0.6 GeV/c p(p) separation: pT andlt; ~1.2 GeV/c  K p Energy Dependence of Antiparticle to Particle Ratios:  Energy Dependence of Antiparticle to Particle Ratios p/p K–/K+ A+A central, near mid-rapidity particle ratios increase with energy net baryon density is rapidly decreasing GOOD CONDITIONS FOR QGP FORMATION at sNN = 200 GeV in Au+Au central collisions: baryochemical potential: B = 27  2 MeV energy density:  = ~ 5 GeV /fm3 , 0 = 1 fm, nucl-ex/0410022 Slide7:  in AA collisions 'BULK' of hadrons is produced at low transverse momentum 'TAIL' of transverse momentum distribution at high-pT originates from hard partonic scatterings 0.2andlt;yp andlt;1.4 Charged Hadron Transverse Momentum Distributions in Au+Au collisions at sNN = 200 GeV centrality: 0-15% mid-rapidity  PRC RC in press nuc-ex/0401006  PLB 578 (2004) 297 PLB 578 (2004) 297 TAIL BULK invariant yields particle density Slide8:  parton nucleus t = - a few fm/c parton t = 0 fm/c hard partonic scattering t = + a few fm/c hadronization jet of hadrons leading hadron of high pT t = + a few fm/c scattered partons pass through hot and dense medium Hard partonic scatterings occur early in AA collision. Scattered partons can probe the dense and hot medium created in AA collision detector nucleus if scattered partons loose energy then the number of leading hadrons will be suppressed ('jet quenching') High-pT Probes Nuclear Modification Factor RAA :  RAA „hard collisions' „soft collisions' pT(GeV/c) Nuclear Modification Factor RAA RAA=1 (Ncoll scaling), lack of nuclear effects, small cross section for hard partonic scattering Ncoll - number of binary inelastic NN interactions in AA ,m, NN data: p+ p (UA1) at 200 GeV p+ p (ISR) at 62.4 GeV Slide10:  RAuAu for Charged Hadrons in Au+Au Collisions at sNN = 200 GeV suppression of high-pT hadron production is observed strongest effect is seen in most central collisions High-pT Suppression :  High-pT Suppression Final state effects? energy loss in medium initial state effects possible in d+Au no final state effects no suppression in d+Au collisions indicates that final state effects are responsible for suppression in Au+Au central Au+Au: d +Au: Initial state effects? gluon saturation: suppression of high parton density (g+g-andgt; g) Color Glass Condensate d+Au at 200 GeV is a control experiment Slide12:  RdAu for Charged Hadrons, sNN = 200 GeV d+Au control experiment indicates that suppression of particle production in central Au+Au collisions at sNN = 200 GeV is a consequence of final state effects PRL 91 (2003) 072302 RdAu Au+Au mid-rapidity, 0.2andlt;yandlt;1.4 medium created in Au+Au collisions is strongly interacting no suppression in d+Au collisions Low-pT Spectra of Identified Charged Particles in Central Au+Au at sNN = 200 GeV:  Low-pT Spectra of Identified Charged Particles in Central Au+Au at sNN = 200 GeV no enhancement in low-pT yields for pions is observed flattening of (p+p) spectra down to very low pT, consistent with transverse expansion of the system |T= 229 MeV for (++-) 293 MeV for (K++ K-) 392 MeV for (p + p) PRC RC in press nucl-ex/0401006  medium created in Au+Au collisions is strongly interacting Slide14:  RAuAu for Charged Hadrons at sNN = 62.4 GeV nucl-ex/0405003 (Au+Au, 62.4 GeV) RHIC Physics Run 2004 RAuAu at 62.4 GeV is significantly higher than at 200 GeV for all centralities within the studied pT range RAuAu Energy Dependence of RAA:  Energy Dependence of RAA nucl-ex/0405003 central Pb+Pb and Au+Au collisions, near mid-rapidity RAA andgt; 1 at sNN = 17.2 GeV RAA andlt; 0.2 at sNN = 200 GeV smooth evolution of RAA with energy Slide16:  pT(GeV/c) yields normalized by Npart weakly depend on centrality Nuclear Modification Factor RAANpart 0 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 Ncoll scaling 45-50% 25-35% 15-25% 0-6% Npart - number of participating (wounded) nucleons in AA nucl-ex/0405003, Au+Au:  62.4 GeV,  200 GeV Factorization of Energy and Centrality Dependence of RAANpart at sNN = 62.4 and 200 GeV:  yield per participant (or RAANpart) changes by less than 25% for both energies in centrality range from 60 to 340 participants. centrality evolution is the same at both energies: RAANpart = RPCNpart (Npart) * f(sNN ) Factorization of Energy and Centrality Dependence of RAANpart at sNN = 62.4 and 200 GeV nucl-ex/0405003 Summary:  Summary Au+Au: almost net-baryon free environment, energy density ~ 5 GeV/fm3 strong suppression of high-pT charged hadron yields in central collisions at 200 GeV (~ 5 times at pT ~ 5 GeV) no evidence for enhanced production of very low-pT pions flattening of p+p spectra at low-pT, strong radial flow in the system, RAuAu at 62.4 GeV is significantly higher than RAuAu at 200 GeV factorization of energy and centrality dependence of RAuAuNpart approximate Npart scaling of hadron yields d+Au: no suppression of charged hadron yields at high-pT (at mid-rapidity) suppression in central Au+Au is final state effect Conclusions:  Conclusions STRONGLY INTERACTING, HIGH DENSITY AND ALMOST NET-BARYON FREE MEDIUM IS CREATED AT THE HIGHEST RHIC ENERGY IN CENTRAL Au+Au COLLISIONS particle ratios high-pT suppression low-pT spectra Triggering on Collisions & Centrality :  Triggering on Collisions andamp; Centrality Coincidence between Paddle counters at Dt = 0 defines a valid collision Paddle + ZDC timing reject background Central Peripheral HIJING +GEANT Glauber calculation Model of paddle trigger Data Data+MC RdAu as a Function of Pseudo-rapidity( = - ln tan(/2)):  RdAu as a Function of Pseudo-rapidity ( = - ln tan(/2)) nucl-ex/0406017, PRC in press nucl-ex/0406017, PRC in press positive  is in deuteron direction with increasing , RAA decreases model constraints: Color Glass Condensate mT Scaling in d+Au vs Au+Au:  PRC in press nucl-ex/0401006 d+Au Scale uncertainty: 15% Not feed-down corrected Au+Au Spectra normalized at 2 GeV/c mT Scaling in d+Au vs Au+Au RAA at low energy (fixed target experiments) :  RAA at low energy (fixed target experiments) Initial state effects RSAu RPbPb RpA Cronin effect Elab = 200 AGeV, sNN = 19.4GeV Pb+Pb: Elab =158 AGeV, sNN = 17.3 GeV RSS multiple scatterings pT broadening =andgt; RAA andgt;1 Factorization of RAA(sNN,centrality):  Factorization of RAA(sNN,centrality) For bandlt;10.5 fm: Centrality  Ncoll pT (GeV/c) nucl-ex/0405003 Slide25:  EPS2003 - Aachen 38 Theory Calculations Cronin Effect: X.N. Wang, Phys. Rev C61, 064910 (2000). Attributed to initial state multiple scattering. Implemented by Q2(pt) dependent Gaussian kt broadening 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)

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