5 QM06 JHLee

Nuclear Induced Particle Suppression at Large-xF at RHIC: 

Nuclear Induced Particle Suppression at Large-xF at RHIC J.H. Lee Physics Department Brookhaven National Laboratory For BRAHMS Collaboration

Slide2: 

At the RHIC energies, hard scattering processes at high-pT become important Partons are expected to loose energy in the dense matter Different rapidities provide different densities of the medium: Sensitive to the dynamics “Dialing” initial condition channel Largest medium effect at mid-rapidity (“Scale” to multiplicity)? Rapidity dependent high-pT suppression factors: provide information on dynamical medium effect at fixed time y~0 high-y Rapidity Dependent High-pT Measurement

RCP and RAuAu vs  for AuAu @200 GeV : 

RCP and RAuAu vs  for AuAu @200 GeV

“High”-pT Particle Suppression at Forward rapidities: 

“High”-pT Particle Suppression at Forward rapidities Expected forward “enhanced” physics processes: Shadowing, Gluon saturation, Phase-space constraint/Energy conservation … With competing physics processes: Partonic energy loss, Multiple scattering, Recombination …

Forward Tomography: Dynamics + Geometry : 

Forward Tomography: Dynamics + Geometry G. Barnaföldi, Lévai, Papp, Fai: nucl-ph/0609023 Shadowing+MS+Energy Loss “Extracted“ opacity indicate longitudinally traveling Protons see less colored field Not a prediction: Assuming rapidity independent suppression factor

Particle Suppression due to Energy Conservation at Forward Rapidities/Large-xF: 

Particle Suppression due to Energy Conservation at Forward Rapidities/Large-xF Universal suppression mechanism at large xF seen in data for various reactions Expected no particles produced as xF  1 due to energy conservation; more multiple interactions (more gluon radiation) make the effect larger in nuclei “Sudakov suppression” Kopeliovich et al: PRC72 (2005) xF= 2pz/√s

“Extended” Longitudinal Scaling of Centrality dependence: RCPNpart : 

“Extended” Longitudinal Scaling of Centrality dependence: RCPNpart Extended range of limiting fragmentation behavior on centrality dependence of particle production: Factorization of Centrality and Energy dependence PHOBOS: nucl-ex/0509034

BRAHMS Data/Acceptance: pT vs xF at √sNN = 200 and 62 GeV: 

BRAHMS Data/Acceptance: pT vs xF at √sNN = 200 and 62 GeV FS MRS Strong pT-xF correlation due to limited spectrometer solid angle acceptance Measurements from BRAHMS Mid-Rapidity Spectrometer (MRS) and Forward Spectrometer (FS) “Dynamic” xF binning in pT 0.2 GeV/c RCP for centrality dependence in pT-xF: RCP(0-20/40-70%),(20-40/40-70%) √sNN = 200 GeV √sNN = 62 GeV

RCP(h-) vs xF in Au+Au at √sNN = 200 and 62 GeV : 

RCP(h-) vs xF in Au+Au at √sNN = 200 and 62 GeV Rcp (0-20%) < Rcp (20-40%): Centrality dependent suppression in xF<0.6 More suppression as xF increases at fixed pT (0.3 ~ 2.2 GeV/c) For the soft Rcp increase and maximize at pT ~ 1 GeV/c Statistical errors only shown Systematic Uncertainties: 10% (p-to-p) + 10% (normalization) MRS, FS h-

RCP(h+) vs xF in Au+Au at √sNN = 200 and 62 GeV : 

RCP(h+) vs xF in Au+Au at √sNN = 200 and 62 GeV MRS, FS h+

RCP(proton) vs xF in Au+Au at √sNN = 200 and 62 GeV : 

RCP(proton) vs xF in Au+Au at √sNN = 200 and 62 GeV MRS, FS p protons at high-xF at the kinematic range dominates form initial protons Yet similar behavior with h-

Summary: 

Summary Nuclear modification factor Rcp for charges hadrons and proton for √sNN = 200 and 62 GeV: -Rcp decrease with xF at given pT -Scaling-like behavior with xF indicating Energy conservation might play a significant role in addition to dynamical suppression mechanism at forward region Constraint/input for more coherent/complete theoretical understanding on dynamics of particle suppression/production at RHIC

Back-up Slides: 

Back-up Slides

RCP (h-) in dAu : 

RCP (h-) in dAu Stronger dependence of RCP on xF RCP continuously increase with pT

Recombination model at high-xF in AuAu at 62 GeV : 

Recombination model at high-xF in AuAu at 62 GeV R. Hwa and C. Yang: nucl-th/060503 Parton recombination without shower parton dominates forward particle production Loosening up kinematic limit and enhance particle production at high-xF for peripheral collisions Protons are more efficiently produced at large-xF (valence quark dominance)

y vs xF: 

y vs xF