Quark Matter 2006 November 18, 2006

Westfälische Wilhelms-UniversitätMünster

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 ReygersUniversity of Münster

Germanyfor the WA98 collaboration

2 Klaus Reygers, Quark Matter 2006


The question is …

Strong evidence for QGP formation

Characterization of the medium(dNgluon/dy 1500)

High-pT-hadron suppression at RHIC

What can we say at CERN SPS energies?



Is there Jet Quenching at sNN = 17.3 GeV?We don’t know!

A+AAA

AA T p+p

d / d

d / dTN p

RT ps

=´

No measured p+p reference at same energy

Nuclear kT enhancement not well understood at sNN ~ 17 GeV

Parameterizationfrom Blattnig et al:Large uncertainty!

Blattnig et al.,Phys. Rev. D 62 (2000) 094030

D. d’Enterria, Phys. Lett. B 596 (2004), 32

p+W @ s = 19.4GeV

Parton energy lossdNgluon/dy = 400 – 600

C. Blume, nucl-ex/0609022



Cronin Enhancement at sNN = 17.3 GeV

Cronin enhancement:

Slightly larger in A+A than in p+A

Strongly model dependent: Maximum enhancement factors between ~2 and ~4

Calculation without parton energy loss:

I. Vitev, M. Gyulassy, PRL 89, 252301,2002

Cronin + shadowing

Expect to take out effect of Cronin enhancement on RAA to large extent with p+Pb reference

Barnaföldi et al., nucl-th/0307062

X.N. Wang, PRC 61, 064910, 2000

I. Vitev, M. Gyulassy

sNN = 17 GeV



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

0 spectra published:

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

Eur.Phys.J.C23:225-236,2002



WA98 Experiment

Minimum bias trigger

High Energy Photon Trigger(pT, > ~ 0.7 GeV/c)

0p

3.5 < < 5.5

2.1 < < 3.0



Calibration and Peak Extraction

Same calibration as in Pb+Pb run

Confirmed with comparison to GEANT simulation

0 peak position in GEANT simulation

p+C p+C

0 peak width in GEANT simulation



Spectra in p+C and p+Pb

Transition to high-pT photon sample at pT = 1.4 GeV/c

Similar pT reach as in Pb+Pb

0 in sNN = 17.3 GeV p+A

preliminary



Cross Check: Comparison to NA49

NA49, hep-ex/0606028

Ratio: WA98 / NA49

sNN = 17.3 GeV p+C

Good agreement with charged pions from NA49

preliminary



RpPb with p+C Reference

RpPb consistent with 1 at high pT

Hint of Cronin enhancement

coll p+C p+PbpPb

coll Tp+Pb p+C

d / d

d / d

TN N pR

N N p= ×

coll p+C1.7 0.2N = ±

coll p+Pb4.1 0.4N = ±

Effect of minimum biastrigger threshold taken into account

preliminary

p+C reference



p+C as p+p Reference

No indication of Cronin enhancement in p+C from comparison to NA49 p+p

Agreement with Blattnig parameterization within errors

p+CpC

coll Tp+C p+p

d / d

d / d

TN pR

N N p=

´

preliminary preliminary

NA49, Eur. Phys. J. C 45, 343 (2006)



RAA in central Pb+Pb at sNN = 17.3 GeV

preliminaryp+C reference

preliminary

p+B A+AAA

A+A T p+B

d / d

d / dT

T N pR

T N p= ×

Proton-nucleus reference measured at same energy:

nuclear overlap function

0-12.7% most central Pb+Pb

p+Pb reference

0-12.7% most central Pb+Pb

0 suppression with respect to p+Pb reference in central Pb+Pb (RAA ~ 0.7 for 0 − 12.7%)

inelX+Y coll NNX+Y

/T N s=



RAA in Pb+Pb with p+C Reference:Centrality Dependence

Ncoll,Pb+Pb = 78 ± 12

p+C A+AAA

A+A T p+C

d / d

d / dT

T N pR

T N p= ×

inelA+A coll NNA+A

/T N s=

inelp+C coll NNp+C

/T N s=

Ncoll,Pb+Pb = 207 ± 21 Ncoll,Pb+Pb = 408 ± 41 Ncoll,Pb+Pb = 569 ± 57 Ncoll,Pb+Pb = 712 ± 71 Ncoll,Pb+Pb = 807 ± 81 preliminary

0 RAA ~ 0.4 in 1% most central Pb+Pb collisions (p+C reference)



RAA in Pb+Pb with p+Pb Reference:Centrality Dependence

p+Pb A+AAA

A+A T p+Pb

d / d

d / dT

T N pR

T N p= ×

inelA+A coll NNA+A

/T N s=

inelp+Pb coll NNp+Pb

/T N s=

Ncoll,Pb+Pb = 78 ± 12 Ncoll,Pb+Pb = 207 ± 21 Ncoll,Pb+Pb = 408 ± 41 Ncoll,Pb+Pb = 569 ± 57 Ncoll,Pb+Pb = 712 ± 71 Ncoll,Pb+Pb = 807 ± 81

0 RAA ~ 0.4 in 1% most central Pb+Pb collisions (p+Pb reference)

preliminary



0 Suppression in Central Pb+Pb

0 in Pb+Pb at sNN = 17.3 GeV

preliminary

0 suppression in Pb+Pb at sNN = 17.3 GeV for Npart > ~300



Summary

0’s from sNN = 17.3 GeV p+C and p+Pb used as reference for RAA

0 suppression at high pT in central Pb+Pb

Looking forward to extraction of dN/dygluon

1% most central:Ncoll,Pb+Pb = 807 ± 81

preliminary



Backup slides



Comparison to other RpA’s



Comparison to WA80



Cronin Enhancement in p+A at sNN = 17.3 GeV

Cronin Enhancement:

Up to a factor 2 for A 200

Large differences between models!

pT (GeV/c)

Rp

+A

Models calculations for p+A at sNN = 17.3 GeV:

Barnaföldi et al., nucl-th/0307062

Quark Matter 2006 November 18, 2006

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