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

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Presentation on theme: "Mid-Rapidity Hadron Production Studied with the PHENIX detector at RHIC Joakim Nystrand Universitetet i Bergen for the PHENIX Collaboration."— Presentation transcript:

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

2 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October What is PHENIX? PHENIX = Pioneering High Energy Nuclear Interaction eXperiment A large, multi-purpose nuclear physics experiment at the Relativistic Heavy-Ion Collider (RHIC)

3 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October A world-wide collaboration of  500 physicists from 51 Institutions in 12 countries The PHENIX collaboration

4 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October The PHENIX detector 2 Central Tracking arms 2 Muon arms Beam-beam counters Zero-degree calorimeters (not seen)

5 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October 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 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October Example of a central Au+Au event at  s nn =200 GeV

7 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October Centrality Definition Centrality  impact parameter Two measures: Np : Number of participating nucleons N coll : Number of binary (nucleon- nucleon) collisions

8 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October Centrality Determinartion For each centrality bin, and are calculated from a Glauber model. Centrality 0 – 10%955  94325  3 10 – 20%603  59235  5 20 – 30% 374  40167  5

9 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October 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 Multiplicity How many particles are produced (at mid-rapidity)? How does the multiplicity scale with centrality, N p or N coll ? B=0 Experimental Method

10 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October 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 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October 200 GeV130 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 Multiplicity at  s=200 GeV

12 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October PHENIX preliminary 200GeV/130GeV Stronger increase in Hijing than in data for central collisions Multiplicity ratio (200/130) GeV

13 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October Variation with  s nn To guide the eye

14 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October  0  Identification with EmCal Background subtracted Original spectrum

15 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October K. Adcox et al. (PHENIX Collaboration) Phys. Rev. Lett. 88(2002)022301 Suppressed  0 yield at high p T A remarkable observation: Yield above p T  2 GeV/c scales with N coll in peri- pheral collisions but is suppressed in central collisions! A possible indication of ”jet-quenching” Bjorken (1982), Gyulassy & Wang (PRL(1992)1480), HIJING

16 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October The ratio R AA Quantify the deviation from binary scaling through R AA : Au+Au 200 GeV S.S. Adler et al. (PHENIX Collaboration) PRL 91(2003)072301. p+p 200 GeV S.S. Adler et al. (PHENIX Collaboration) hep-ex/0304038, to be published in PRL.

17 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October Suppression of charged hadrons A similar suppression seen also for charged hadrons at high p T. Au+Au 200 GeV S.S. Adler et al. (PHENIX Collaboration) nucl-ex/0308006, submitted to PRC.

18 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October Suppression at high p T 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. Intial or Final State Effect? d+Au 200 GeV S.S. Adler et al. (PHENIX Collaboration) PRL 91(2003)072303.

19 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October 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 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October The yield is extracted by fitting the m 2 spectrum to a function for the signal (gaussian) + background (1/x or e -x )

21 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October Correction for acceptance and efficiency  normalized d and d p T spectrum: The spectrum has been fit to an exp. function in m T,  exp( -m T /T) More about the slopes (T eff ) later…

22 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October How are nuclei and anti-nuclei formed in ultra- relativistic heavy-ion interactions? 1. Fragmentation of the incoming nuclei. Dominating mechanism at low energy and/or at large rapidities (fragmentation region). No anti- nuclei. 2. Coalescence of nucleons/anti-nucleons. Dominating mechanism at mid-rapidity in ultra- relativistic collisions. Only mechanism for production of anti-nuclei.

23 Coalescence A deuteron will be formed when a proton and a neutron are within a certain distance in momentum and configuration space. where p d =2p p and B 2 is the coalescence parameter, B 2  1/V. Assuming that n and p have similar d 3 N/dp 3 This leads to: Imagine a number of neutrons and protons enclosed in a volume V:

24 The reality is more complicated… B 2 depends on p T  not a direct measure of the volume Possible explanation: Radial flow.

25 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October 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 B 2 with p T. The detailed variation depends on the choice of nucleon density and flow profile.

26 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October For the special case Linear flow profile + Gaussian density distribution T eff independent of fragment mass, T eff (d) = T eff (p)  The gaussian parameterization + linear flow profile give too little weight to the outer parts of the fireball, where the flow is strongest. Experimentally, dT eff = 515  26 MeVpT eff = 326  6 MeV * * mid-central collisions, 40-50% centrality. dT eff = 488  26 MeV pT eff = 331  6 MeV *

27 Joakim Nystrand, Universitetet i Bergen PT03, Copenhagen 9-10 October Conclusions Nearly logarithmic increase in multiplicity per participant with  s AGS  SPS  RHIC  yield suppressed at high p T 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. A lot of new exciting data (only a fraction was shown in this talk)

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