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Why does high-pt suppression persist at forward rapidity?

Why does high-pt suppression persist at forward rapidity?. I.G. Bearden ( for the BRAHMS collaboration) Niels Bohr Institute, Københavns Universitet. Outline. Introduction Experiment R AA Results 200GeV Au+Au 62GeV Cu+Cu & Au+Au Model Comparisons Summary.

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Why does high-pt suppression persist at forward rapidity?

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  1. Why does high-pt suppression persist at forward rapidity? I.G. Bearden ( for the BRAHMS collaboration) Niels Bohr Institute, Københavns Universitet Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  2. Outline • Introduction • Experiment • RAA • Results • 200GeV Au+Au • 62GeV Cu+Cu & Au+Au • Model Comparisons • Summary Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  3. It’s Broad RAnge Hadron Magnetic Spectrometers! 90° 30° that can rotate from 2.3° to 30° and 30° to 90° (MRS) 2.3° 30° The BRAHMS Experiment Two small solid angle spectrometers (FS and MRS) provide excellent PID over broad range in y-pT Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  4. Nuclear Modification Quantified by: - yield relative to that from N+N collisions, scaled for the nuclear geometry (Nbin) • Cronin Enhancement • Shadowing/Saturation • Jet-quenching Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  5. Charged hadron pT spectra 200GeV Au+Au Nb: filled are +, open -, drawn lines are BRAHMS p+p data Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  6. RAA for charged hadrons at high pT, the charged hadron yields produced in most central 0-10% Au+Au collisions are suppressed compared to binary scaled p+p yields Little change in RAA as function of eta BRAHMS Preliminary Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  7. RAA @ 62.4 GeV ~0 ~3.1 Au+Au BRAHMS Preliminary Cu+Cu BRAHMS Preliminary I.G.Bearden, Niels Bohr Institute

  8. How to make pT=2GeV/c p=2.8GeV/c p=28GeV/c   BRAHMS Preliminary Caveat emptor! Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  9. RAuCu0- 10% & 40-60% I.G.Bearden, Niels Bohr Institute

  10. RAuCu with same Ncoll at Midrapidity I.G.Bearden, Niels Bohr Institute

  11. RAuCu mid vs. forward 62.4GeV (10%) Midrapidity Forward (3.1) RAuCu pT Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  12. BRAHMS PRELIMINARY RAuCu with same ‘radius’ I.G.Bearden, Niels Bohr Institute

  13. RAA for identified particles (200GeV) the charged pion yields are suppressed by a factor of ~ 2-3 as compared with binary scaled p+p pion yields. RAA for pions is independent of rapidity the proton and antiproton yields in central Au+Au at 200 GeV do not show suppression, baryon meson difference remains protons BRAHMS Preliminary pions Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  14. RAA at 62.4 GeV, y=0 BRAHMS Preliminary BRAHMS Preliminary I.G.Bearden, Niels Bohr Institute

  15. RAA, y>3, 62GeV, top 10% central I.G.Bearden, Niels Bohr Institute

  16. Hydro+Jet: Interplay between Soft and Hard Calculation based on two models with CGC as initial conditions: 3D hydrodynamic model (Hydro)‏ dynamics of high pT partons (Jet)‏ pT,cross is the point for Yieldsoft=Yieldhard pT,cross moves toward high pT with mass of particles because of the effects of radial flow. T.Hirano & Y.Nara(’03), PRC69(2004)034908 Au+Au at b=2 fm PT, cross~ 1.8 GeV/c for  2.7 GeV/c for K 3.7 GeV/c for p Interesting region Intermediate pT (2<pT<3.5 GeV/c)‏ Pion hard,Protonsoft y=0 Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  17. Model comparison I pT spectra for charged hadrons in 200 GeV Au+Au reasonably well described by the hydro+jet model calculation at η=3.2 Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  18. Model comparison II Barnafoldi et al. hep-ph 0609023 opacity n = L/l L – effective length of matter l – mean free path less jet quenching + stronger initial effects at higher rapidities maintain rapidity independent NMF Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  19. Is RAA an appropriate measure? Two rather different Models both reproduce RAA. RAA only tells us that we only ‘see’ particles from near Hot&dense surface? ~15 GeV Renk, Eskola, PRC 75, 054910 (2007) Wicks,Horowitz,Djordjevic,Gyulassy NPA 784, 426 (2007) Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

  20. Summary • At 200GeV, intermediate pT constant behavior vs. y • For 62.4GeV, pronounced changes from mid to forward rapidity. • + suppressed for 62.4 y=3.4, p “suppressed” but not partonically • RAA flat for same mean radius (<R>). Why? • Hydro+jet looks good, but... • RAA not a good model descriminator Quark Matter '08 Jaipur India I.G.Bearden, Niels Bohr Institute

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