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The BRAHMS Experiment at RHIC - an overview -

This article provides an overview of the BRAHMS Experiment at RHIC, including the Relativistic HI Collider, global detectors, spectrometers, and PID. It discusses topics such as charged particle multiplicity, relativistic HI collision evolution, particle spectra, and nuclear stopping. The collaboration and institutions involved in the experiment are also mentioned.

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The BRAHMS Experiment at RHIC - an overview -

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  1. The BRAHMS Experiment at RHIC - an overview - Claus Jørgensen, Niels Bohr Institute for the BRAHMS Collaboration XLII International Winter Meeting on Nuclear Physics Bormio, January 25 – February 1, 2004

  2. What I’ll talk about in the next 35 min. The BRAHMS Experiment - The Relativistic HI collider - global detectors - spectrometers & PID Charged Particle Multiplicity - Au+Au and d+Au @ sNN=200GeV Relativistic HI collision evolution Particle Spectra from Au+Au @ sNN=200GeV - Kinetic freeze out - Chemical freeze out - Nuclear Stopping

  3. The BRAHMS Collaboration I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J.Brzychczyk4, B. Budick6, H. Bøggild7 , C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1, E. Enger12, J. J. Gaardhøje7, M. Germinario7, K. Grotowski4 , K. Hagel8, O. Hansen7, A.K. Holme12, H. Ito11, E. Jacobsen7, A. Jipa10, J. I. Jordre10, F. Jundt2, C.E.Jørgensen7, R. Karabowicz4 , T. Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3, A. Makeev8, B. McBreen1, M. Mikkelsen12, M. Murray8, J. Natowitz8, B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4, F. Rami2, D. Roehrich9, B. H. Samset12, D. Sandberg7, S. J. Sanders11, R.A.Sheetz1, Z.Sosin3, P. Staszel7, T.S. Tveter12, F.Videbæk1, R. Wada8, A.Wieloch3 and I. S. Zgura10 1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France 3Jagiellonian University, Cracow, Poland, 4Institute of Nuclear Physics, Cracow, Poland 5Johns Hopkins University, Baltimore, USA, 6New York University, USA 7Niels Bohr Institute, University of Copenhagen, Denmark 8Texas A&M University, College Station. USA, 9University of Bergen, Norway 10University of Bucharest, Romania,11University of Kansas, Lawrence,USA 12 University of Oslo Norway 56 physicists, 12 institutions…

  4. BRAHMS BRAHMS The Relativistic Heavy Ion Collider Au+Au Top energy: sNN=200GeV d+Au p+p

  5. The BRAHMS Experiment Midrapidity Spectrometer Zero Degree Calorimeter Front Forward Spectrometer Global Detectors Back Forward Spectrometer

  6. TMA & SiMA: for centrality determination. Silicon Strips Plastic Scintillator Tiles 20-30% 40-50% 30-40% 10-20% 5-10% 0-5% more central collisions Global Detectors Beam-Beam counters: for vertex determination. ZDC counters: at 18 meters. Measure spectator neutrons.

  7. NEW!!! d+Au compared to models: HIJING, AMPT and saturation model. submitted to PRL (nucl-ex/0401025) -4 -2 0 2 4  Au d Charged Particle Multiplicity 0-5% 5-10% 10-20% 20-30% 30-40% 40-50% 0-5% central Au+Au: Total charged particle multiplicity: 4630370 (PRL 88, 202301(2002))

  8. Limiting Fragmentation Shift the dNch/d distribution by the beam rapidity, and scale by Npart. Lines up with lower energy  limiting fragmentation d+Au sNN=200GeV andsNN=19.4GeV lines up on the d-side. Not on the Au side! Au+Au sNN=200GeV Au+Au sNN=200GeV (0-5% and 30-40%) Au+Au sNN=200GeV (0-5%) Pb+Pb sNN=17GeV (9.4%)

  9. Midrapidity Spectrometer: 30º-90º Full Forward Spectrometer: 2.3º-15º Front Forward Spectromter: 2.3º-30º The BRAHMS Spectrometers

  10. TOFW 2 cut TOFW TOF1 TOF2  / K 3 GeV/c 4.5 GeV/c 2 GeV/c TOF2 TOF1 K / p 3.5GeV/c 5.5GeV/c 7.5GeV/c PID I – Time-of-flight TIME-OF-FLIGHT Particle Separation: pmax (2 cut)=

  11. C4 RICH C1 CHERENKOV RICH: Cherenkov light focused on spherical mirror  ring on image plane Ring radius vs momentum gives PID  / K separation 20 GeV/c Proton ID up to 35 GeV/c (2 settings) PID II - Cherenkov

  12. The BRAHMS Acceptance Transverse momentum [GeV/c] rotatable spectrometers give unique rapidity coverage : Broad RAnge Hadron Magnetic Spectrometers Rapidity

  13. Particle Yields I By combining all data sets and averaging over the number of collisions, we get the final invariant yields over a broad range of phase-space Ph.D. thesis by Peter Christiansen Djamel Ouerdane

  14. Pions: power law Kaons: exponential Protons: Gaussian Particle Yields II Top 5% central collisions

  15. 0 1 2 3 4 5 rapidity Rapidity Densities Integrated multiplicities (Gaussian fit) N() ~ 1780 N(+) ~ 1760 N(K+) ~ 290 N(K) ~ 240 N(pbar)~ 85 Total number of +K+p > 4000 (consistent with dNch/d measurement)

  16. Transverse Dynamics  K • ,K,p spectra • described by • blast wave model • Parametrization including: • Freeze out temperature • Flow velocity • System geometry • -size and flow profile • (Schnedermann et al. PRC48(1993)) p BRAHMS preliminary

  17. T, Transverse Dynamics Temperature vs y Flow versus y BRAHMS preliminary BRAHMS preliminary • T115 Mev, T0.7c at y=0 • Flow velocity decreases with rapidity. • Lower density  lower pressure  less flow • Temperature increases. • Lower density  faster freeze out  higher temperature

  18. 250 Increasing y RHIC chemical freeze out 200 PRL90,102301 (2003) Chemical Temperature Tch [MeV] SPS 150 AGS 100 kinetic freeze out SIS 50 atomic nuclei 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] Ratios – Chemical freeze out Hadron Gas Statistical model (grand canonical ensemble) reproduces (all) particle ratios  Tch, B Freeze out at QCD phase boundary. Different sources (B,T) at different rapidities?

  19. Prediction: dN/dy (y) Gaussian of width  given by (simplified model): NA49 AGS Ok as a 1st approximation BUT systematic difference remains : flatter top, tails broader => more longitudinal flow Bjorken vs. Landau Entropy ~ Pion production Expansion ~ isentropic Pion gas = 3D relativistic fluid [L.D. Landau, Izv. Akad. Nauk SSSR 17 (1953) 52 P.Carruthers, M.Duong-van, PRD 8 (1973) 859] BRAHMS

  20. stopping transprarancy Stopping or Transparancy?

  21. Net-proton measured up to y = 3 AGS : high stopping RHIC: more transparent Net Proton Rapidity Distribution Net-proton rapidity densities (top 5% central collisions) BRAHMS, submitted to PRL, nucl-ex/0312023

  22. Gaussians in pz: Gaussians in pz: y = 2.03  0.16 y = 2.00  0.10 6 order polynomial Nuclear Stopping I Net-baryon after feed-down & neutron corrections Total E=25.72.1TeV

  23. My LHC prediction: y = 2.2, E/A=2800GeV ? (Ebeam/A=3500GeV, ybeam=8.9) SPS, RHIC,LHC net-baryons empirical scaling scaling broken 9 Nuclear Stopping II Bjorken: “There exist a leading-baryon effect. That is, the original baryons of a projectile is found in fragments of comparable momentum (more precisely of rapitity within ~2-3 units of the rapidity of the source).” (PRD 27, 140 (1983))

  24. Energy (in GeV) p : 3108 p : 428 K+ : 1628 K- : 1093 + : 5888 - : 6117 • 0 : 6004 • n : 3729 • n : 513 • K0 : 1628 • K0 : 1093 •  : 1879 • : 342 sum: 33.4 TeV produced: 24.8TeV • 35 TeV (EbeamNpart) • of which 25 TeV are • carried by produced • particles. NB: the method is very sensitive to the tails of the dN/dy dist. (10-15%) Energy Balance • Fit , K and p distributions (dN/dy and mT vs y) •  total energy of , K and p • Assume reasonable distribution • for particles we don’t detect (0,n,…) • Calculate the total energy…

  25. Kinetic freeze out: • Spectra described by • blast wave model • Fast collective motion, • T115 MeV,   0.7c • Multiplicity • more than 4500 charged • particles produced • in the central collisions • limiting fragmentation • Net baryons: • y ybeamscaling broken • y  2 • 25 TeV left for particle • production • Chemical freeze out: • Ratios (all) descibed by • statistical model • T170Mev, B 29Mev at y=0 • freeze out at QCD • phase boundary • QGP and CGC? • signatures in the high pT region? • smoking gun? • talk by Bjorn Samset on Friday Conclusions

  26. Backup I High pT suppression in central Au+Au collisions. High pT enhancement in d+Au! The smoking gun of QGP?

  27. Backup II Parametrization: dN/d = Npart+Ncoll “soft” + “hard” (what do we learn from that?)

  28. Backup III • Thermal (Tch) and chemical (ni) equilibration at chemical freeze out • Tch and ‘s (+ system size), gives ni's from grand canonical ensemble. In praticle ratios the system size cancels out. • Conservation laws: Baryon Number, Strangeness, Isospin

  29. Backup IV versus energy T and T are anti-correlated: versus system size Blast wave:

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