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Forward Hadron experimental overview

This overview discusses interesting RHIC results at mid-rapidity, exploring initial state effects and nuclear modification factors. It also covers the PHENIX Detector and the use of stopped tracks and decay muons for analysis. The presentation concludes with a summary of the current understanding and future studies in the field.

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Forward Hadron experimental overview

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  1. Forward Hadron experimental overview Anuj K. Purwar LANL PHENIX Muon Workshop ’05 Santa Fe

  2. So far … • Interesting RHIC results at mid-rapidity: Initial (color deconfined medium) or final state (saturation)? Anuj K. Purwar, Santa Fe Muon Workshop

  3. Why forward? • New regime of parton physics at low-x • Can be reached by going to large rapidities. For Au nuclei (Going N to S) For deuterons (Going S to N) Anuj K. Purwar, Santa Fe Muon Workshop

  4. Initial state effects • DIS experiments revealed nucleons to consist of partons. • Gluon PDFs diverge at small-x • QCD being non-abelian allows: g+g->g • Can lead to saturation Anuj K. Purwar, Santa Fe Muon Workshop

  5. Nuclear modification factor: RCP • Rcp is defined as • If Au+Au like p+p incoherent then, RCP =1 • RCP suppressed in Au+Au. • Enchanced in d+Au. Anuj K. Purwar, Santa Fe Muon Workshop

  6. The PHENIX Detector gold deuteron South Muon arm : -2.2 < h <-1.2 North Muon arm : 1.2 < h <2.4 Anuj K. Purwar, Santa Fe Muon Workshop

  7. 2 Tracker Absorber Identifier Collision 2 1 3 4 Collision range GAP 4 3 2 1 0 Symbols Hadron Detector Absorber Muon Major Sources of Hadronic Tracks 1 : Hadrons, interacting and absorbed (98%) 2 : Charged/K's,"decaying" before absorber (≤1%) 3 : Hadrons, penetrating and interacting ("stopped") 4 : Hadrons, "punch-through" Anuj K. Purwar, Santa Fe Muon Workshop

  8. Stopped tracks • MuID has several layers of steel, so deeper a particle penetrates, greater is the chance that it is a muon. • Use shallow MuID layers (Gap 2 & 3) to select stopped hadrons. Muons in deep gap Hadrons in shallow gaps Muon peak Hadronic tail Anuj K. Purwar, Santa Fe Muon Workshop

  9. Decay Muons • Light hadrons like pions and kaons can decay into muons before reaching the MuID. • The decay probability of a meson with momentum p is proportional to the distance (L) between collision vertex and absorber: • Hence by looking at the the z-vertex distribution for events with single muon candidates, we can separate the muons that come from pions/kaons from other contributions. Anuj K. Purwar, Santa Fe Muon Workshop

  10. Decay muons and z dependence Phys. Rev. Lett. 94, 082302 (2005) ) • Pion and kaon decay contributions have z dependence. • Other contributions (e.g. D mesons) are flat. Anuj K. Purwar, Santa Fe Muon Workshop

  11. Rcp vs h (1.5 < pT 4.0 GeV/c) Phys. Rev. Lett. 94, 082302 (2005) • Suppression forward and enhancement backward Anuj K. Purwar, Santa Fe Muon Workshop

  12. Rcp vs pT at forward & backward rapidity Phys. Rev. Lett. 94, 082302 (2005) • RCP rather independent of pT Anuj K. Purwar, Santa Fe Muon Workshop

  13. BRAHMS RdAu at forward rapidity ( ) BRAHMS, PRL 93, 242303 Anuj K. Purwar, Santa Fe Muon Workshop

  14. RdAu from PHOBOS PRC 70, 061901(R) Anuj K. Purwar, Santa Fe Muon Workshop

  15.  dependence of RdAu Clear rapidity trend of RdAu Anuj K. Purwar, Santa Fe Muon Workshop

  16. STAR Pseudo-rapidity yield asymmetry vs pT PRC 70, 064907 Anuj K. Purwar, Santa Fe Muon Workshop

  17. Model: ColorGlassCondensate D. Kharzeev hep-ph/0307037 Increasing y • Parton model => nucleon consists of “free” point-like constituents: quarks and gluons. • ColorGlassCondensate is a QCD based theory for the dense partonic matter at small-x and predicts depletion of scattering centers through gluon fusion processes. kis transverse momentum of partons Qsis saturation scale Anuj K. Purwar, Santa Fe Muon Workshop

  18. Model: Coherent Multiple Scattering Qiu & Vitev hep-ph/0405068 • Depletion of small-x partons in a nucleus compared to those in a nucleon (Shadowing). • Coherent multiple scattering can lead to dynamical nuclear shadowing. • Leads to suppression at forward rapidities/more central events. Anuj K. Purwar, Santa Fe Muon Workshop

  19. Model: Recombination Hwa, Yang and Fries nucl-th/0410111 • Recombination of soft and shower partons leads to a reduction of the soft parton density in the deuteron side. • Explains the forward backward asymmetry and why RCP (protons) > RCP (mesons) at midrapidity. Anuj K. Purwar, Santa Fe Muon Workshop

  20. Summary • All RHIC experiments see suppression at forward direction which increases as function of h. • Forward suppression is qualitatively consistent with several theories from shadowing/saturation type effects to initial state multiple scattering to recombination. • Enhancement at backward rapidity is not so well understood. • Future studies of charm Rcp and yields at forward rapidities in d+Au collisions might distinguish between different models. Anuj K. Purwar, Santa Fe Muon Workshop

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