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