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Ramiro Debbe for the BRAHMS collaboration Physics Department

BRAHMS Overview. 5 th International Conference on Physics and Astrophysics of Quark Gluon Plasma. Ramiro Debbe for the BRAHMS collaboration Physics Department. Outline of the presentation. A brief summary of particle production in Au-Au collisions at √s NN = 200GeV.

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Ramiro Debbe for the BRAHMS collaboration Physics Department

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  1. BRAHMS Overview 5th International Conference on Physics and Astrophysics of Quark Gluon Plasma Ramiro Debbe for theBRAHMScollaboration Physics Department Kolkata India 8-12 February 2005

  2. Outline of the presentation • A brief summary of particle production in Au-Au collisions at √sNN= 200GeV. • Intermediate Pt physics. Pt suppression and the formation of an opaque dense medium and will discuss its behavior as function of rapidity and centrality. • Summary Kolkata India 8-12 February 2005

  3. The BRAHMS Detector MRS FFS BFS Kolkata India 8-12 February 2005

  4. multiplicity [a.u.] TMA BB BB ZDC ZDC INEL Event characterization The centrality of the collision for the results that will be presented is defined as fractions of the total multiplicity measured with the TMA in -2<<2 The centrality of Au-Au collisions can also be defined with the ZDC and BB or TMA correlations. Our triggers are defined with the ZDC and BB, p+p and d+Au collisions were triggered with the INEL detectors. Kolkata India 8-12 February 2005

  5. Charged particle production This is one of the first measurements at RHIC with a multiplicity density unexpectedly low. It may indicate the high degree of coherence in high energy A+A collisions. It already shows a bell shape and a slow growth as function of centrality. Kolkata India 8-12 February 2005

  6. 0 1 2 3 4 5 rapidity Rapidity Densities in Au-Au at sNN = 200 GeV nucl-ex/0403050 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 the dNch/d measurement) The longitudinal expansion does not modify much the shapes of the thermal source or the PDF of the colliding ions. Kolkata India 8-12 February 2005

  7. Pions: power law Kaons: exponential Protons: Gaussian Particle Yields Top 5% central collisions Kolkata India 8-12 February 2005

  8. Transverse Dynamics ,K,p spectra described by blast wave model We see a weak rapidity dependence of both T and   K p • Kinetic frezze out temp. 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 BRAHMS preliminary Kolkata India 8-12 February 2005

  9. Baryon number transport Even at this high energy, there is a non-zero net proton at mid-rapidity. Baryon junctions can have a small-x component that would bring baryon number to mid-rapidity. No weak decay corrections Once the corrections are included: nB=2.03±0.08np Au+Au s=200GeV 0-10% central Kolkata India 8-12 February 2005

  10. Rapidity loss The average rapidity loss at RHIC energies does not scale as the ones measured at lower energy values. 73±6% of the beam energy available for particle production PRL 93, 1020301, (2003) Kolkata India 8-12 February 2005

  11. 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… Kolkata India 8-12 February 2005

  12. Strangeness production Integrated Mid-rapidity RHIC is well beyond the “resonance gas” of CERN. It appears that the production of K- and K+ is becoming “similar”. At forward rapidities, the baryon chemical potential has grown by ~ 5 and we may be entering again a CERN like system. Kolkata India 8-12 February 2005

  13. Particle abundances and statistical models For a fixed chemical freeze out temperature. The ratios of anti-particle to particle correlate along the Becattini et al. calculation based on their statistical model. s =0 Kolkata India 8-12 February 2005

  14. Results from p+p collisions We found remarkable similarity in the baryon number transport in Au+Au and p+p collisions as seen in the anti-proton/proton ratio. The Au+Au results were extracted from 0-20% central events. Kolkata India 8-12 February 2005

  15. Transverse Spin Asymmetries An • An = e /P with P ~40-45% • = (N+ /L+ - N-/L-) / (N+ /L+ + N-/L-) <e>~ +0.022 => AN= +0.05 +- 0.005 +- [0.015] in 0.17 < xF < 0.32 <e>~ -0.035 => AN= -0.08 +- 0.005 +- [0.015] in 0.17 < xF < 0.32 Kolkata India 8-12 February 2005

  16. PT suppression can be related to two possible mechanisms: Modification of the wave function in the initial state Y Quantum evolution at high rapidity. Gluon emmission tamed by fusion.dNg/d(ln1/x) = s (2Ng - Ng2) The growth of the numerator in RABor Rcp is slower than that of the denominator. Cronin type enhancement by coherent multiple scattering at y~0 Kolkata India 8-12 February 2005

  17. pT suppression cont. Energy loss in a medium formed after the collision : Energy loss is encoded in the fragmentation of the final state parton. The number of interactions (each emitting a gluon) depends on the density of the medium. Gluon density of the formed medium (rapidity dependent) Kolkata India 8-12 February 2005

  18. Invariant yields of charged particles in Au+Au and d+Au Kolkata India 8-12 February 2005

  19. Rh=Rcp(h=2.2)/Rcp(h=0) Arsene et al.PRL 91 2003 Kolkata India 8-12 February 2005

  20. RAuAu of Pions and Protons =0 Preliminary =2.2 It is clear that baryons have a different behavior. No feed down corrections applied Kolkata India 8-12 February 2005

  21. d+Au nuclear modification factor The absence of suppression in d+Au at y=0 and back-to-back correlations have been considered necessary conditions to the formation of a dense and opaque medium;the suppression seen in Au+Au is a final state effect. But the possibility of a saturated Au cannot be excluded Kolkata India 8-12 February 2005

  22. Spectra from d-Au and p-p collisions Upper panels show an outline of the data used construct the spectra. At each angle, one or several magnetic field settings were used. Spectra are acceptance and detector efficiency corrected, other corrections as momentum resolution and binning effects were not included. Kolkata India 8-12 February 2005

  23. RdAu as function of rapidity Cronin like enhancement at =0. Clear suppression as  changes up to 3.2 Same ratio made with dn/d follows the low pT RdAu PRL 94 (2004) Minimum bias with < Ncoll> = 7.2±0.3 Kolkata India 8-12 February 2005

  24. Rcp ratios At  =0 the central events have the ratio systematically above that of semi-central events. We see a reversal of behavior as we study events at =3.2 1/<Ncollcentral> NABcentral(pT,h) Rcp= 1/<Ncoll periph> NABperiph(pT,h) Kolkata India 8-12 February 2005

  25. Particle identification in d-Au collisions Kolkata India 8-12 February 2005

  26. Identified particles in d-Au at =3.2 Many protons in the most forward d+Au. Is this beam fragmentation? 80% of the negative charged particles at =3 are pions Kolkata India 8-12 February 2005

  27. RdAu for anti-protons and pions (min bias) This will not be the first time baryons show a different nuclear modification factor. PHENIX reported such difference at y=0 in AuAu and dAu systems Kolkata India 8-12 February 2005

  28. Energy dependence (SPSRHIC) pT=3-4GeV/c pT=3-4GeV/c 40-60% 20-40% 10-20% 0-10% RAuAu at sNN= 62.4 GeV Nuclear modification factor RAuAu - different centrality classes Kolkata India 8-12 February 2005

  29. Rcp of charged hadrons at ~3.2 BRAHMS Preliminary • Strong centrality dependence: Rcp(0-10%) < Rcp(20-40%) • No significant h dependence in 0<h<3.2 • Maximum at pT~2GeV/c • Rcp(+) > Rcp(-) • Systematic Errors - 10-15% overall - 10% p-by-p h~3.2 h~0 h~2.2 BRAHMS PRL 91 (2003) Kolkata India 8-12 February 2005

  30. Rcp for Identified particles at y~3 BRAHMS Preliminary p± K± • Suppression for all particles • maximum at pT~2GeV/c • Rcp(+) ~ Rcp(-) for p, K, p • Rcp(p) > Rcp(K) > Rcp(p) p,pbar • Data Kolkata India 8-12 February 2005

  31. Summary • We have now a wide view of bulk particle production in Au+Au collisions. There are no extended plateaus in the density distributions, ~ 70% of the beam energy is made available for particle production in central Au+Au. • Forward physics has proved to be a fertile ground for discovery and an important ingredient of our understanding of the new medium formed at RHIC. Kolkata India 8-12 February 2005

  32. The BRAHMS Collaboration - 12 institutions- I.Arsene10,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,J. J. Gaardhøje7,M. Germinario7, K. Hagel8, O. Hansen7, H. Ito11, E. Jacobsen7, A. Jipa10, J. I. Jordre10, F. Jundt2, C.E.Jørgensen7, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3, A. Makeev8, B. McBreen1, M. Murray8, J. Natowitz8, B. Neuman11,B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4, F. Rami2, D. Roehrich9, B. H. Samset12, S. J. Sanders11, I. S. Sgura10, R.A.Sheetz1, Z.Sosin3, P. Staszel7, T.S. Tveter12, F.Videbæk1, R. Wada8 ,A.Wieloch3,Z. Yin9 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, Blegdamsvej 17, 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 Kolkata India 8-12 February 2005

  33. Kolkata India 8-12 February 2005

  34. p/p ratios BRAHMS Preliminary Kolkata India 8-12 February 2005

  35. Kolkata India 8-12 February 2005

  36. Kolkata India 8-12 February 2005

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