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Mid-Rapidity Hadron Production Studied with the PHENIX detector at RHIC

Mid-Rapidity Hadron Production Studied with the PHENIX detector at RHIC. Joakim Nystrand Universitetet i Bergen. for the PHENIX Collaboration. A large, multi-purpose nuclear physics experiment at the Relativistic Heavy-Ion Collider (RHIC). What is PHENIX?.

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Mid-Rapidity Hadron Production Studied with the PHENIX detector at RHIC

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  1. Mid-Rapidity Hadron Production Studied with the PHENIX detector at RHIC Joakim Nystrand Universitetet i Bergen for the PHENIX Collaboration

  2. A large, multi-purpose nuclear physics experiment at the Relativistic Heavy-Ion Collider (RHIC) What is PHENIX? PHENIX= Pioneering High Energy Nuclear Interaction eXperiment

  3. The PHENIX collaboration A world-wide collaboration of  500 physicists from 51 Institutions in 12 countries

  4. 2 Central Tracking arms 2 Muon arms Beam-beam counters Zero-degree calorimeters (not seen) The PHENIX detector

  5. Charged particle tracking: • Drift chamber • Pad chambers (MWPC) • Particle ID: • Time-of-flight (hadrons) • Ring Imaging Cherenkov • (electrons) • EMCal (, 0) • Time Expansion Chamber • Acceptance: • || < 0.35 – mid-rapidity •  = 2  90

  6. Example of a central Au+Au event at snn =200 GeV

  7. Centrality Definition Centrality  impact parameter Two measures: Np : Number of participating nucleons Ncoll : Number of binary (nucleon-nucleon) collisions

  8. Centrality Determinartion For each centrality bin, <Np> and <Ncoll> are calculated from a Glauber model. Centrality <Ncoll> <Np> 0 – 10% 95594 3253 10 – 20% 60359 2355 20 – 30% 37440 1675 • • • • • •

  9. B=0 Experimental Method Multiplicity How many particles are produced (at mid-rapidity)? How does the multiplicity scale with centrality, Np or Ncoll? • Combine the hits in PC1 and PC3. • The result is a sum of true combinations (from real tracks) and combinatorial background. • Determine the combinatorial background by event mixing

  10. Multiplicity per 2 participants HIJING X.N.Wang and M.Gyulassy, PRL 86, 3498 (2001) EKRT K.J.Eskola et al, Nucl Phys. B570, 379 and Phys.Lett. B 497, 39 (2001) K. Adcox et al. (PHENIX Collaboration), Phys. Rev. Lett. 86(2001)3500 Au+Au at s=130 GeV

  11. Multiplicity at s=200 GeV 130 GeV 200 GeV HIJING X.N.Wang and M.Gyulassy, PRL 86, 3498 (2001) Mini-jet S.Li and X.W.Wang Phys.Lett.B527:85-91 (2002) EKRT K.J.Eskola et al, Nucl Phys. B570, 379 and Phys.Lett. B 497, 39 (2001) KLN D.Kharzeev and M. Nardi, Phys.Lett. B503, 121 (2001) D.Kharzeev and E.Levin, Phys.Lett. B523, 79 (2001) PHENIX preliminary

  12. Multiplicity ratio (200/130) GeV 200GeV/130GeV PHENIX preliminary Stronger increase in Hijing than in data for central collisions

  13. Variation with snn To guide the eye

  14. Original spectrum Background subtracted 0 Identification with EmCal

  15. Suppressed 0 yield at high pT A remarkable observation: Yield above pT 2 GeV/c scales with Ncoll in peri- pheral collisions but is suppressed in central collisions! A possible indication of ”jet-quenching” Bjorken (1982), Gyulassy & Wang (PRL(1992)1480), HIJING K. Adcox et al. (PHENIX Collaboration) Phys. Rev. Lett. 88(2002)022301

  16. The ratio RAA p+p 200 GeV S.S. Adler et al. (PHENIX Collaboration) hep-ex/0304038, to be published in PRL. Quantify the deviation from binary scaling through RAA: Au+Au 200 GeV S.S. Adler et al. (PHENIX Collaboration) PRL 91(2003)072301.

  17. Suppression of charged hadrons A similar suppression seen also for charged hadrons at high pT. Au+Au 200 GeV S.S. Adler et al. (PHENIX Collaboration) nucl-ex/0308006, submitted to PRC.

  18. Intial or Final State Effect? d+Au 200 GeV S.S. Adler et al. (PHENIX Collaboration) PRL 91(2003)072303. Suppression at high pT in AA vs. pp How about pA (or dA)? Absence of suppression in dA suggest that the effect seen in central AA is due to the dense matter created in the collisions.

  19. Charged-particle Identification Central arm detectors: Drift Chamber, Pad Chambers (2 layers), Time-of-Flight. Combining the momentum information (from the deflection in the magnetic field) with the flight-time (from ToF):

  20. The yield is extracted by fitting the m2 spectrum to a function for the signal (gaussian) + background (1/x or e-x)

  21. Correction for acceptance and efficiency  normalized d and d pT spectrum: The spectrum has been fit to an exp. function in mT,  exp( -mT/T) More about the slopes (Teff) later…

  22. How are nuclei and anti-nuclei formed in ultra-relativistic heavy-ion interactions? • Fragmentation of the incoming nuclei. Dominating mechanism at low energy and/or at large rapidities (fragmentation region). No anti-nuclei. • Coalescence of nucleons/anti-nucleons. Dominating mechanism at mid-rapidity in ultra-relativistic collisions. Only mechanism for production of anti-nuclei.

  23. Coalescence Imagine a number of neutrons and protons enclosed in a volume V: A deuteron will be formed when a proton and a neutron are within a certain distance in momentum and configuration space. This leads to: where pd=2pp and B2 is the coalescence parameter, B2 1/V. Assuming that n and p have similar d3N/dp3

  24. The reality is more complicated… B2 depends on pT not a direct measure of the volume Possible explanation: Radial flow.

  25. A. Polleri, J.P. Bondorf, I.N. Mishustin: ”Effects of collective expansion on light cluster spectra in relativistic heavy ion collisions” Phys. Lett. B 419(1998)19. Introducing collective transverse flow generally leads to an increase in B2 with pT. The detailed variation depends on the choice of nucleon density and flow profile.

  26. For the special case * mid-central collisions, 40-50% centrality. Experimentally, d Teff = 51526 MeV p Teff = 3266 MeV* d Teff = 48826 MeV p Teff = 3316 MeV* Linear flow profile + Gaussian density distribution Teff independent of fragment mass, Teff(d) = Teff(p)  The gaussian parameterization + linear flow profile give too little weight to the outer parts of the fireball, where the flow is strongest.

  27. Conclusions A lot of new exciting data (only a fraction was shown in this talk) • Nearly logarithmic increase in multiplicity per participant with s AGS  SPS  RHIC •  yield suppressed at high pT in central Au+Au collisions. •  yield not suppressed in d+Au collisions  Suppression in central Au+Au collisions is a final state effect, caused by the dense medium. • deuteron/anti-deuteron spectra at mid-rapidity probes the late stages of relativistic heavy ion collisions.

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