M. Botje, Rencontres de Moriond on QCD, March 2004 1
NA49 energy scan results for central Pb-Pb collisions at the SPS
NA49 energy scan results for central Pb-Pb collisions at the SPS
Michiel Botje, NIKHEF
(for the NA49 collaboration)
Aim: search for indications of the onset of deconfinement from a study of the energy
dependence of particle production in central Pb+Pb collisions
Aim: search for indications of the onset of deconfinement from a study of the energy
dependence of particle production in central Pb+Pb collisions
M. Botje, Rencontres de Moriond on QCD, March 2004 2
NA49NA49
Large acceptance hadron spectrometer
Large acceptance hadron spectrometer
PID by dE/dx in TPCs for p > 7 GeV/c
PID by TOF (~60 ps) at mid-rapidity
Centrality selection from spectators in downstream VCAL (not shown)
p/p2 = (0.3 – 7) 10–4 (GeV/c)–1
M. Botje, Rencontres de Moriond on QCD, March 2004 3
NA49 central Pb+Pb data setsNA49 central Pb+Pb data sets
2002300 k7 %20 AGeV
2002400 k7 %30 AGeV
1999700 k7 %40 AGeV
2000300 k7 %80 AGeV
20003000 k20 %158 AGeV
1996800 k10 %158 AGeV
Taken inEvent
StatisticsCentrality
Beam Energy
158, 80, 40 AGeV published in PRC 66(2003)054902 30, 20 AGeV still preliminary
M. Botje, Rencontres de Moriond on QCD, March 2004 4
158 AGeV
Transverse mass spectra at mid-rapidityTransverse mass spectra at mid-rapidity
T
pI
T
mKm
dydmm
dN TTT
TT
sinhcosh01
2
= atanh T
Blast wave fits
Schnedermann, Sollfrank, Heinz: PRC 48(1993)2462
T = kinetic freeze-out temperatureT = transverse flow velocity
Not included in fit: pions (resonance decays) and deuterons (coalescence)
M. Botje, Rencontres de Moriond on QCD, March 2004 5
Transverse mass spectra at lower energiesTransverse mass spectra at lower energies
30 AGeV 20 AGeV
Blast wave model describes spectra at all SPS energies Kinetic freeze-out at T 120-130 MeV and T 0.4-0.5
40 AGeV
M. Botje, Rencontres de Moriond on QCD, March 2004 6
Constant slopes in the SPS energy range
Exponential fits to kaon mT spectra Exponential fits to kaon mT spectra
M. Botje, Rencontres de Moriond on QCD, March 2004 7
Energy dependence of slope parametersEnergy dependence of slope parameters
No rise of inverse slope in SPS energy range Consequence of constant pressure in mixed phase? (van Hove, 1982)
M. Botje, Rencontres de Moriond on QCD, March 2004 8
Rapidity spectra versus energyRapidity spectra versus energy
Large acceptance exptrapolation 4 yields
(Open circles: reflection about mid-rapidity)
Also and
M. Botje, Rencontres de Moriond on QCD, March 2004 9
Energy dependence of yieldsEnergy dependence of yields
1/4NNs
Increase of w with energy gets steeper at the SPS
Increase of slope by about a factor of 1.3
Increase of initial # d.o.f (g) by 1.34 3?
SMES: statistical model of the early stage:
(pion yield is measure of entropy)
Gazdzicki & Gorenstein, Acta Phys. Pol. B30(1999)2705)
M. Botje, Rencontres de Moriond on QCD, March 2004 10
Energy dependence of kaon yieldsEnergy dependence of kaon yields
P+P
Monotonic increase of K–/– with a hint of structure at 30 AGeV Sharp peak in K+/+ confirmed by the 20 and 30 AGeV data K+/+ constant between 158 AGeV and RHIC
M. Botje, Rencontres de Moriond on QCD, March 2004 11
Statistical hadron-gas modelStatistical hadron-gas model
Assume hadron species populated according to phase space (Fermi, Hagedorn): extract T and B at chemical freeze-out from fits to all particle yields (Beccattini PRC 69(2004)024905)
Dashed line: smooth interpolation of freeze-out curve (Cleymans and Redlich PRL 81(1998)5284)
Phase boundary: estimate by Fodor and Katz JHEP 203(2002)14
Hadrochemical freezeout params close to phase boundary at SPS
M. Botje, Rencontres de Moriond on QCD, March 2004 12
Hadron-gas model: K/ ratiosHadron-gas model: K/ ratios
Interplay between T and B leads to weak maximum in K+/+
Model captures the trend (by construction) but fails to describe sharp peak in the K+/+ ratio
M. Botje, Rencontres de Moriond on QCD, March 2004 13
x 6
x 15
Energy dependence of hyperon productionEnergy dependence of hyperon production
s show a distinct maximum at 30AGeV
Weak maximum for s and s
Y =
Hadron-gas model: Braun-Munzinger, Cleymans, Öschler, Redlich Nucl. Phys. A697 (2002) 902
x6
4 yields
@ 30, 40, 80, 158 AGeV @ 40, 158 AGeV
M. Botje, Rencontres de Moriond on QCD, March 2004 14
From Bratkovskaya et al, nucl-th/0401031
Both UrQMD and HMD fail to describe the sharp maximum in the K+/+ ratio
Comparison to hadron-string modelsComparison to hadron-string models
HSDHSD
UrQMDUrQMD
M. Botje, Rencontres de Moriond on QCD, March 2004 15
SMES predictionSMES prediction
SMES:
Hadronic phase: Es rises rapidly with temperature
Partonic phase: Es 0.21 independent of T
Peak in Es reflects phase transition in the model
(Gazdzicki, Gorenstein: Acta Phys. Pol. B30(1999)2705)
hadr
onic
partonic
mixed
M. Botje, Rencontres de Moriond on QCD, March 2004 16
Comparison of models Comparison of models
Data presently favour the SMES
Onset of deconfinement at the SPS?
Challenge to model builders: Can observed anomalous energy dependence be accomodated in a hadronic scenario?
M. Botje, Rencontres de Moriond on QCD, March 2004 17
Conclusion from the SPS energy scanConclusion from the SPS energy scan
Anomalies observed in central Pb+Pb collisions steepening rate of increase of pion production sharp peak in the strange particle to pion ratio constant slopes of the K+ and K– mT spectra
Present models without deconfinement in the early phase do not reproduce the details of the energy dependence
Phase transition scenario in Statistical Model of the Early stage is compatible with the data
Anomalies observed in central Pb+Pb collisions steepening rate of increase of pion production sharp peak in the strange particle to pion ratio constant slopes of the K+ and K– mT spectra
Present models without deconfinement in the early phase do not reproduce the details of the energy dependence
Phase transition scenario in Statistical Model of the Early stage is compatible with the data