Centrality Dependence of Neutral Pion Production in d+Au Collisions at = 200 GeV

1. q Peak extraction geometric acc. 0 reconstr. Eff. Energy scale Trigger eff. G1 Norm. Scale Conv. Correction Total error pT indep. 5.0%(5.0%) 5.0%(5.0%) 2.8%(2.8%) 2 GeV 3.0%(3.0%) 4.0%(4.0%) 4.0%(4.0%) - 10%(10%) 6 GeV 2.0%(2.0%) 4.0%(4.0%) 9.0%(9.0%) 5.0%(10.0%) 14%(16%) 10 GeV 2.0%(2.0%) 4.5%(4.5%) 11.0%(11.0%) 3.0%(3.0%) 15%(15%) type A B B B B C C q q Type A Type C Type B q  p0  Polynomial 1 Constant for syst. error PbSc (PbGl) Quantify using the Nuclear Modification Factor RAA AuAu: RAuAu - High pTp0 Suppression AuAu : Centrality Dependence of RAA AA d+Au Collision Centrality Determination Centrality Dependence of d+Au p0 Spectra p0 RdA PbGl and PbSc Comparison d Au RdAu p0 Centrality Dependence RdAup0 Centrality Dependence vs. Theory p0 and Charged p Comparison (Ratio to p fit) PHENIX Preliminary RdAu Central to peripheral Systematic Errors Summary and Conclusions Nucl-th/0308029, Accardi and Gyulassy Centrality Dependence of Neutral Pion Production in d+Au Collisions at = 200 GeV Henner Büsching Brookhaven National Laboratory for the PHENIX Collaboration • PbSc • Highly segmented leadscintillator • sampling Calorimeter • Module size: 5.5 cm x 5.5 cm x 37 cm • PbGl • Highly segmented lead glass • CherenkovCalorimeter • Module size: 4 cm x 4 cm x 40 cm • Two Technologies - very important for systematic error understanding! • Differences: • Different response to hadrons • Different corrections to get linear • energy response Leading Particle Real/Mix Hard parton scatterings in nucleon-nucleon collisions produce jets of particles. In the presence of a dense strongly interacting medium, the scattered partons will suffer soft interactions losing energy (dE/dx~GeV/fm). “Jet Quenching” Real Norm Mix Hadrons Real - Norm Mix (pseudorapidity |h| < 0.35) Reference case: d+Au No produced medium p0gg pT =1-1.5 GeV Nuclear overlap function • Centrality dependence similar to • predictions of Color Glass Condensate • (AKA Gluon Saturation) • Suggests Initial state effect!?! • Need p+Au (d+Au) AuAu AuAu Nuclear thickness function Peripheral AuAu - consistent with Ncol scaling (large systematic error) Binary scaling Compare A+A to p+p cross section from Glauber model Large suppression in central AuAu – close to participant scaling at high PT Factor 5 “Nominal effects”: R < 1 in regime of soft physics R = 1 at high-pT where hard scattering dominates R > 1 due to kT broadening (Cronin) AA Participant scaling AA AA More central collisions PRL 91 (2003) 072301 D.Kharzeev, E.Levin, L.McLerran hep-ph/0210332 PRL 91 (2003) 072301 Suppression: R < 1 at high-pT Centrality selection : Beam-Beam Counter South (Au) (BBC, |h|=3~4) Sum BBC Charge Multiplicity ExtractNcollandNpartbased on Glauber model Central PHENIX Preliminary Peripheral PHENIX Preliminary Centrality <Ncoll> • 0-20 % : 15.0 ± 1.0 • 20-40 % : 10.4 ± 0.7 • 40-60 % : 6.9 ± 0.6 • 60-88 % : 3.2 ± 0.3 • Combined PbSc and PbGl results • p0 Yields measured to ~10 GeV/c Side view PHENIX Preliminary • Strong suppression of high pT particle production in central Au+Au at = 200 GeV with respect to scaled p+p reference • No suppression in 200 GeV d+Au • Weak increase with centrality (Cronin effect) • d+Au centrality dependence opposite to Au+Au • Suppression in Au+Au is caused by properties of created hot and dense medium PHENIX Preliminary • Comparisson to most • Peripheral sample • pT uncorrelated (or correlation not known) pT correlated error - all points move to same direction • pT correlated error - all points move by the same factor • (normalization error)