P.Seyboth: Indications for the onset of deconfinement in Pb+Pb collisions at the CERN SPS from NA49...

P.Seyboth: Indications for the onset of deconfinement in Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)

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Indications for the Onset of Deconfinement in Pb+Pb Collisions at the CERN SPS from NA49

• Introduction• Search for structure in the energy dependence of

– Inclusive particle production– E-by-E fluctuations, BE correlations, flow

• Summary and conclusion

P.Seyboth, MPI für Physik, Munich for the NA49 collaboration


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Introduction: Pb+Pb collisions at top SPS energy

• Initial energy density exceeds the critical value predicted by lattice QCD ( 1 GeV / fm3 )

• Strong collective behavior– anisotropic and radial flow– transverse expansion of the matter droplet by factor 2

• Proposed signatures for deconfinement observed– Strangeness enhancement– Low-mass dilepton enhancement– J/Ψ,Ψ’ yield suppression

• Signatures not unique• Search for a threshold by varying the energy for the

largest collision system (central Pb+Pb reactions)


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The NA49 Detector

Target: 20cm liquid H2 or Pb foil VCAL detects projectile spectatorsΔp/p2 = 7 (0.3) • 10-4 (GeV/c)-1 (VTPC-1, VTPC+MTPC) dE/dx resolution 3 – 6 %TOF resolution ~ 60 ps

p > 7 GeVdE/dx

forward rapidity2,5 < p < 10 GeV :

TOF + dE/dxat midrapidity


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Pb+Pb collision at 158A GeV


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NA49 energy scan program of central Pb+Pb collisions

search for structure in the energy dependence of observables which may be linked to the onset of deconfinement

Beam Energy

CentralityEvent

StatisticsTaken in

158A GeV 10 % 800 k 1996

158A GeV 20 % 3,000 k 2000

80A GeV 7 % 300 k 2000

40A GeV 7 % 700 k 1999

30A GeV 7 % 400 k 2002

20A GeV 7 % 300 k 2002preliminary

PRC 66(2003) 054902


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Rapidity spectra

(open dots from reflection at ycm= 0)

Extrapolation 4π yields

also: Ξ, Ω


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Transverse mass spectra at mid-rapidity 158A GeV

many spectra measured

well described by fireball model assuming common temperature and flow

“blast wave”:

(Schnedermann,Sollfrank, Heinz : PRC 48 (1993) 2462)


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Transverse mass spectra at lower energy:

40A GeV 30A GeV 20A GeV

“kinetic” freeze out at T 120 –130 MeV, βT 0.4 – 0.5 at SPS

“blast wave” model describes spectra at all SPS energies


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Particle yields – statistical model

• hadron species populated according to phase space probabilities (max.entropy) (Fermi,Hagedorn)

• strangeness sector not fully saturated (Rafelski)

• statistical model successful, T, μB, γS, V

• larger value of γS in A+A due to relaxation of local strangeness conservation

(fits by F.Becattini et al, PRC69(2004)024905)


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Particle yields at 40A, 80A GeV – statistical model

at lower energies μB increases, while T decreases slightly


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Global view - Phase diagram

• statistical model describes yields from SIS to RHIC energy• T of “hadrochemical” freeze out increases SIS RHIC• μB decreases (increase of pion production)

• freeze out at E 1 GeV per particle dashed line

(Lattice-QCD phase boundary: Fodor,Katz JHEP04(2004)050) hadrochemical freeze out parameters

approach the phase boundary at SPS

(Cleymans and Redlich, PRL 81(1998) 5284 )

QGP

Hadrons

1st order


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Energy dependence - π yields• increase of <π>/<NW> with energy gets steeper in SPS range• π deficit changes to enhancement compared to p+p

• pions are most abundant particle species measure of entropy in statistical models

SMES: statistical model of the early stage

Increase of initial d.o.f . g between AGS and SPS ? 1/4

NNs

(Gazdzicki,Gorenstein : Acta Phys.Pol. B30(1999)2705)

) ( 1.5 -


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Energy dependence - ratio of K ,Λ yields to pions

• sharp peak of K+/π+ ratio• smooth rise of anti-Λ/π ( s quarks)

• similar peak in Λ/π ratio• structure in K–/π– ( s quarks)

hadronic models donot (yet ?) reproduce the sharp peak

)(2

1


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Energy dependence – ratio of strange hadrons to pions

hadronic

mixed

partonic

strangeness to pion ratio peaks sharply at the SPS

SMES explanation: - entropy, number of s,sbar quarks conserved from QGP to freezeout - ratio of strange/nonstrange d.o.f. rises rapidly with T in hadron gas - Es drops to predicted constant level above the deconfinement threshold

0.21

E

g g g

g 0.74

NN

gdu

sSSS

1/4

NNs

0S

- K 4 )K K( 2 K :note onset of deconfinement at SPS ?

hadr

onic

mixed

partonic


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Energy dependence – inverse slope parameters

• inverse slope parameter T of K+ and K- constant at SPS

T/m - e

dydmm

dN T

TT

• approximately constant pressure and temperature in mixed phase ?

(L.van Hove, PLB89(1982)253 M.Gorenstein et al.,PLB567(2003)175)


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Energy dependence - average transverse mass

Increase of <mT> for abundantly produced particles ( π, K, p) slows sharply at the lowest SPS energy


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The Event-by-Event K/π ratio

Increased fluctuation signal at

lower beam energies

Bea

m E

nerg

y

σ2dyn = σ2

data – σ2mixed

NA49 preliminary

max.likelihood fit for each event


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The Event-by-Event p/π ratioB

eam

Ene

rgy

NA49 preliminary

The distribution of the E-by-E p/π ratiois narrower for data than mixed events. Effect of baryon resonance decay ?


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Electric charge fluctuations

• Smaller in a QGP than in a hadron gas

(Jeon,Koch,Asakawa,Heinz,Müller)

• Effect of hadronisation ?) q - (q Zq - q z

z - Z

N

1ii

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Nq

Central Pb+Pb collisions 158A GeV

Global charge conservation

1 /1, totchchGCCq NN


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QGP signature possibly masked by effect of resonance decays

GCCqqq ,

No clear energy dependenceof charge fluctuations at SPS

Remove effect of global charge conservation :


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BE correlations: energy dependence of radius parameters

kT ~ 0.15 GeV/c

Rlong increases slowly

Rside constant

Rout constant

no evidence of anomalies or “soft point” of EOS


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Anisotropic flow v2

Initial anisotropy ε in non-central collisions transformed intomomentum anisotropy v2 by pressure at early reaction stage

Smooth increase with collision energy towards hydrodynamic model prediction

ε = (<y2>+<x2>)/(<y2>-<x2>)

SPS RHIC


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Conclusion from the energy scan at the SPS

• structure observed at low SPS energy in central Pb+Pb collisions – the rate of increase of pion production steepens– the strange particle to pion ratio peaks sharply– constancy of the slope of π and K mT- spectra

• no evident anomalies in e-by-e fluctuations (K/π, charge), BE correlations and flow• present models without deconfinement in the early phase do not reproduce details of energy dependence• reaction scenario with onset of deconfinement at the SPS can explain the observed structure

plan to continue SPS program with lighter nuclei: • role of the initial volume in the onset of deconfinement • search for the predicted critical point


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The NA49 collaboration


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Extra slides for discussion


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Estimate of initial energy density at 158A GeV

• from projectile energy loss and interaction volume:

• from transverse energy production and Bjorken’s model:

initial energy density ε > εc 1 GeV/fm3

3130 GeV/fm 13

3

4/67.0 / ArsmVE NNN

1/3

0

3

2

A 1.12 R

fm/c 1 with

GeV/fm 3.2

)/()/(

oT RddENA49, PRL 75 (1995) 3814


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Λ , Ξ and Ω rapidity spectra


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Transverse mass spectra in p+p collisons at 158 GeV

consistent with common temperature T 145 MeV

“blast wave” model fit consistent with small βT


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Statistical model for p+p collisions at 158 GeV


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Energy dependence of K , Λ yields

carriers of s quarks carriers of s quarks

)( 1.5


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Energy dependence of total yield of s, s carriers

carriers of s quarks carriers of s quarks

)( 1.5


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System size dependence of strangeness production at 158A GeV

disappearance ofcanonical suppression for Npart > 60


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Balance function for oppositely charged particles

158A GeV

(NA49 preliminary)

similar narrowingat SPS and RHIC


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Event-by-Event estimation of the particle ratios

• Vary relative normalization of the particle species (K/,p/) in the probability density function

• Extract ratios with maximum likelihood fit

One Event:

Probability density function:

Fit dE/dx spectra in 4D binning

Event Ensemble:<

dE

/dx>

<d

E/d

x>

log(Ptot [GeV])

log(Ptot [GeV])

log(Ptot [GeV])

<d

E/d

x>

<dE/dx>


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v2(pT) at SPS and RHIC


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Fluctuations of <pT> vs system size at 158A GeV

selected range: 4.0 < yπ< 5.5 corrected for limited 2-track resolution


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Fluctuations of <n-> vs system size at 158A GeV

(NA49 preliminary)

correction for fluct. inprojectile participants:

selected range: 4 < y < 5.5


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Multiplicity fluctuations at 158A GeV

(NA49 preliminary)

P.Seyboth: Indications for the onset of deconfinement in Pb+Pb collisions at the CERN SPS from NA49...

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Transcript of P.Seyboth: Indications for the onset of deconfinement in Pb+Pb collisions at the CERN SPS from NA49...