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Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC

Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC. nucl-ex/0410022, 2004. Adam Trzupek The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences Kraków, Poland. for the Collaboration.

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Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC

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  1. Charged Hadron Spectra and Ratios in d+Au and Au+Au Collisions from PHOBOS Experiment at RHIC nucl-ex/0410022, 2004 Adam Trzupek The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences Kraków, Poland for the Collaboration 4th Budapest Winter School on Heavy Ion Collisions (December 1st-3rd 2004) in Budapest, Hungary

  2. 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

  3. PHOBOS Detector TOF SpecTOF T0 counter Paddle Trigger counter Spectrometer Magnet Paddle Trigger counter multiplicity, vertex and calorimeter detectors are not labeled (see Russell Betts talk) T0 counter

  4. z -x F E D C X[cm] B A . . Be pipe 01020Z [cm] . pT and PID Measurement in PHOBOS Spectrometer 70 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 10 cm • pT = 0.2 - ~5 GeV/c • track curvature in B field => p,charge • dE/dx in Si, ToF => mass • pT = 0.03 - 0.2 GeV/c • low-pparticles stop • in silicon wafers => p, mass • B field negligible => no charge identification

  5. PID Measurement in PHOBOS Spectrometer pT > 0.2 GeV/c pT = 0.03 - 0.2 GeV/c p K <dE/dx>  Etot =  dEi , i=A, ... ,E Mpi= Ei dEi/dx Mp = < Mpi > /K separation: pT < ~0.6 GeV/c p(p) separation: pT < ~1.2 GeV/c

  6. PHOBOS 130 GeV PRL 87 (2001)102301 PHOBOS 200 GeV PRC 67 (2003) 0211901 Energy Dependence of Antiparticle to Particle Ratios A+A central, near mid-rapidity K–/K+ p/p particle ratios increase with energy net baryon density is rapidly decreasing at sNN = 200 GeV in Au+Au central collisions: baryochemical potential:B = 27  2 MeVenergy density:  =~ 5 GeV /fm3 , 0 = 1 fm, nucl-ex/0410022 GOOD CONDITIONS FOR QGP FORMATION

  7. Charged Hadron Transverse Momentum Distributions in Au+Au collisions at sNN = 200 GeV particle density invariant yields BULK centrality: 0-15% mid-rapidity  PRC RC in press nuc-ex/0401006 PLB 578 (2004) 297 TAIL 0.2<yp<1.4 PLB 578 (2004) 297 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

  8. High-pT Probes Hard partonic scatterings occur early in AA collision. Scattered partons can probe the dense and hot medium created in AA collision t = - a few fm/c t = 0 fm/c t = + a few fm/c t = + a few fm/c nucleus nucleus parton parton hard partonic scattering scattered partons pass through hot and dense medium hadronization jet of hadrons if scattered partons loose energy then the number of leading hadrons will be suppressed (”jet quenching”) leading hadron of high pT detector

  9. Nuclear Modification Factor RAA ,m, Ncoll - number of binary inelastic NN interactions in AA NN data: p+ p (UA1) at 200 GeV p+ p (ISR) at 62.4 GeV RAA „hard collisions” RAA=1 (Ncoll scaling), lack of nuclear effects, small cross section for hard partonic scattering „soft collisions” pT(GeV/c)

  10. RAuAu for Charged Hadrons in Au+Au Collisions at sNN = 200 GeV PLB 578 (2004) 297 1 d2 NAuAu/ dpTd RAuAu= 45-50% 35-45% RAuAu <Ncoll> d2 NNN/ dpTd Ncoll scaling mid- peripheral 25-35% 15-25% 0-6% 6-15% central pT (GeV/c) suppression of high-pT hadron production is observed strongest effect is seen in most central collisions

  11. High-pT Suppression central Au+Au: Final state effects? Initial state effects? gluon saturation: suppression of high parton density (g+g-> g) Color Glass Condensate energy loss in medium d +Au: 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 d+Au at 200 GeV is a control experiment

  12. RdAufor Charged Hadrons, sNN = 200 GeV mid-rapidity, 0.2<y<1.4 PRL 91 (2003) 072302 no suppression in d+Au collisions RdAu 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 Au+Au medium created in Au+Au collisions is strongly interacting

  13. mT = pT2+mh2 Low-pT Spectra of Identified Charged Particles in Central Au+Au at sNN = 200 GeV PRC RC in press nucl-ex/0401006  |T= 229 MeV for (++-) 293 MeV for (K++ K-) 392 MeV for (p + p) 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 medium created in Au+Au collisions is strongly interacting

  14. RAuAu for Charged Hadrons at sNN = 62.4 GeV nucl-ex/0405003 (Au+Au, 62.4 GeV) RHIC Physics Run 2004 RAuAu RAuAu at 62.4 GeV is significantly higher than at 200 GeV for all centralities within the studied pT range

  15. at high-pT: Energy Dependence of RAA central Pb+Pb and Au+Au collisions, near mid-rapidity nucl-ex/0405003 smooth evolution of RAA with energy RAA > 1 at sNN = 17.2 GeV RAA < 0.2 at sNN = 200 GeV

  16. Nuclear Modification Factor RAANpart <Ncoll> Au+Au Glauber Model 1 d2 NAA / dpTd RAANpart= <Npart/2> d2 NNN/ dpTd Ncoll ~ Npart4/3 <Npart> b(fm) Npart - number of participating (wounded) nucleons in AA nucl-ex/0405003, Au+Au: 62.4 GeV,  200 GeV Ncoll scaling 45-50% 25-35% 15-25% 0-6% pT(GeV/c) yields normalized by Npart weakly depend on centrality 0 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

  17. Factorization of Energy and Centrality Dependenceof RAANpartat sNN = 62.4 and 200 GeV nucl-ex/0405003 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 )

  18. 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

  19. Conclusions particle ratios high-pT suppression low-pT spectra STRONGLY INTERACTING, HIGH DENSITY AND ALMOST NET-BARYON FREE MEDIUM IS CREATED AT THE HIGHEST RHIC ENERGY IN CENTRAL Au+Au COLLISIONS

  20. Positive Paddles Negative Paddles NegativeCerenkov PositiveCerenkov Negative ZDC Positive ZDC Au Au PN PP x z Triggering on Collisions & Centrality • Coincidence between Paddle counters at Dt = 0 defines a valid collision • Paddle + ZDC timing reject background Data Data+MC • HIJING +GEANT • Glauber calculation • Model of paddle trigger Peripheral Central

  21. 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

  22. mT Scaling in d+Au vs Au+Au PRC in press nucl-ex/0401006 Au+Au Spectra normalized at 2 GeV/c d+Au Scale uncertainty: 15% Not feed-down corrected

  23. Elab= 200 AGeV, sNN = 19.4GeV RSAu RAA at low energy (fixed target experiments) Pb+Pb: Elab=158 AGeV, sNN = 17.3 GeV RPbPb RSS RpA multiple scatterings pT broadening => RAA >1 Cronin effect Initial state effects

  24. 62.4 GeV 200 GeV Factorization of RAA(sNN,centrality) For b<10.5 fm: Centrality  Ncoll pT (GeV/c) nucl-ex/0405003

  25. 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 38

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