Hadron Suppression and Nuclear kT Enhancement Studied with Neutral Pions from p+C, p+Pb, and Pb+Pb Collisions at sNN = 17.3 GeV Quark Matter 2006 November 18, 2006 Klaus Reygers University of Münster Germany for the WA98 collaboration
The question is … High-pT-hadron suppression at RHIC Strong evidence for QGP formation Characterization of the medium (dNgluon/dy 1500) What can we say at CERN SPS energies? 2 Klaus Reygers, Quark Matter 2006
Is there Jet Quenching at sNN = 17.3 GeV? We don’t know! p+W @ s = 19.4GeV Parameterization from Blattnig et al: Large uncertainty! Blattnig et al., Phys. Rev. D 62 (2000) 094030 Parton energy loss dNgluon/dy = 400 – 600 D. d’Enterria, Phys. Lett. B 596 (2004), 32 C. Blume, nucl-ex/0609022 No measured p+p reference at same energy Nuclear kT enhancement not well understood at sNN ~ 17 GeV 3 Klaus Reygers, Quark Matter 2006
Cronin Enhancement at sNN = 17.3 GeV Calculation without parton energy loss: Cronin enhancement: Slightly larger in A+A than in p+A Strongly model dependent: Maximum enhancement factors between ~2 and ~4 sNN = 17 GeV Cronin + shadowing I. Vitev, M. Gyulassy, PRL 89, 252301,2002 I. Vitev, M. Gyulassy Barnaföldi et al., nucl-th/0307062 X.N. Wang, PRC 61, 064910, 2000 Expect to take out effect of Cronin enhancement on RAA to large extent with p+Pb reference 4 Klaus Reygers, Quark Matter 2006
Idea of this Analysis: p+C and p+Pb as Reference for Pb+Pb RAA Reaction System Year Pb+Pb at sNN = 17.3 GeV 1994, 1995, 1996 p+C, p+Pb at sNN = 17.3 GeV 1996 p0 spectra published: Eur.Phys.J.C23:225-236,2002 Presented in this talk p + C: → Replacement for p+p reference (Ncoll 1.7 expect small Cronin enhancement) p + Pb: → Study nuclear kT enhancement by comparing to p+C → Reference for RAA in Pb+Pb: partially removes effect of Cronin enhancement 5 Klaus Reygers, Quark Matter 2006
WA98 Experiment High Energy Photon Trigger (pT,g > ~ 0.7 GeV/c) Minimum bias trigger 6 Klaus Reygers, Quark Matter 2006
Calibration and Peak Extraction p+C p+C p0 peak position in GEANT simulation Same calibration as in Pb+Pb run Confirmed with comparison to GEANT simulation p0 peak width in GEANT simulation 7 Klaus Reygers, Quark Matter 2006
p0 Spectra in p+C and p+Pb p0 in sNN = 17.3 GeV p+A preliminary Transition to high-pT photon sample at pT = 1.4 GeV/c Similar pT reach as in Pb+Pb 8 Klaus Reygers, Quark Matter 2006
Cross Check: Comparison to NA49 Ratio: WA98 / NA49 sNN = 17.3 GeV p+C preliminary NA49, hep-ex/0606028 Good agreement with charged pions from NA49 9 Klaus Reygers, Quark Matter 2006
RpPb with p+C Reference Effect of minimum bias trigger threshold taken into account preliminary RpPb consistent with 1 at high pT Hint of Cronin enhancement 10 Klaus Reygers, Quark Matter 2006
p+C as p+p Reference NA49, Eur. Phys. J. C 45, 343 (2006) preliminary preliminary No indication of Cronin enhancement in p+C from comparison to NA49 p+p Agreement with Blattnig parameterization within errors 11 Klaus Reygers, Quark Matter 2006
RAA in central Pb+Pb at sNN = 17.3 GeV Proton-nucleus reference measured at same energy: 0-12.7% most central Pb+Pb p0 nuclear overlap function preliminary p+C reference 0-12.7% most central Pb+Pb p0 suppression with respect to p+Pb reference in central Pb+Pb (RAA ~ 0.7 for 0 − 12.7%) p0 preliminary p+Pb reference 12 Klaus Reygers, Quark Matter 2006
RAA in Pb+Pb with p+C Reference: Centrality Dependence Ncoll,Pb+Pb = 712 ± 71 Ncoll,Pb+Pb = 807 ± 81 Ncoll,Pb+Pb = 569 ± 57 Ncoll,Pb+Pb = 408 ± 41 Ncoll,Pb+Pb = 207 ± 21 preliminary Ncoll,Pb+Pb = 78 ± 12 p0 RAA ~ 0.4 in 1% most central Pb+Pb collisions (p+C reference) 13 Klaus Reygers, Quark Matter 2006
RAA in Pb+Pb with p+Pb Reference: Centrality Dependence Ncoll,Pb+Pb = 712 ± 71 Ncoll,Pb+Pb = 807 ± 81 Ncoll,Pb+Pb = 569 ± 57 Ncoll,Pb+Pb = 408 ± 41 Ncoll,Pb+Pb = 207 ± 21 preliminary Ncoll,Pb+Pb = 78 ± 12 p0 RAA ~ 0.4 in 1% most central Pb+Pb collisions (p+Pb reference) 14 Klaus Reygers, Quark Matter 2006
p0 Suppression in Central Pb+Pb p0 in Pb+Pb at sNN = 17.3 GeV preliminary p0 suppression in Pb+Pb at sNN = 17.3 GeV for Npart > ~300 15 Klaus Reygers, Quark Matter 2006
Summary p0’s from sNN = 17.3 GeV p+C and p+Pb used as reference for RAA p0 suppression at high pT in central Pb+Pb Looking forward to extraction of dN/dygluon 1% most central: Ncoll,Pb+Pb = 807 ± 81 preliminary 16 Klaus Reygers, Quark Matter 2006
Backup slides 17 Klaus Reygers, Quark Matter 2006
Comparison to other RpA’s 18 Klaus Reygers, Quark Matter 2006
Comparison to WA80 19 Klaus Reygers, Quark Matter 2006
Cronin Enhancement in p+A at sNN = 17.3 GeV Models calculations for p+A at sNN = 17.3 GeV: Cronin Enhancement: Up to a factor 2 for A 200 Large differences between models! Rp+A pT (GeV/c) Barnaföldi et al., nucl-th/0307062 20 Klaus Reygers, Quark Matter 2006