P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Indications for the Onset of Deconfinement in Pb+Pb collisions at the SPS

• Introduction• Search for structure in the energy dependence of

– Inclusive particle yields– E-by-E fluctuations: K/π, Q– BE correlations – Anisotropic flow

• Summary

P.Seyboth, MPI für Physik, München for the NA49 Collaboration

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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- and intermediate-mass dilepton enhancements– J/Ψ,Ψ’ yield suppression

• Signatures not specific for deconfinement Search for a threshold by varying the energy for the

largest collision system (central Pb+Pb reactions) SPS energy scan: 20,30,40,80,158 GeV/nucleon

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Pb+Pb collision at 158A GeV

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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) constant βT ; π , d excluded from fit

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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early freezeout of multistrange hyperons ?

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

(assuming radially constant βT)

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Rapidity spectra

(open dots from reflection at ycm= 0)

Extrapolation 4π yields

also: Ξ, Ω

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Rapidity spectra: energy dependence of width

• width close to Landau prediction for pions• better agreement with linear increase with ybeam

• clear mass hierarchy at SPS (exclude p, Λ, Ξ containing leading beam quarks)• 4π and mid-rapidity ratios differ systematically

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

• incease of γS= 0.5 → 0.8 from p+p to A+A shows: relaxation of canonical suppression not enough !

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

( NA49 data )

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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

• pions are most abundant produced 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 -

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Energy dependence of total yield of s,s quarks

: carriersquark s

0 1) 0 1)

2)

+

0 2)

0 3) 0 3

-

+- + )

0

-

s s -

K K

quark carriers:

K ,

+ ,

- quark carriers:

K ,

+ ,

,

, ,

,

energy dependence of yields changes at 30A GeV

sharp peak, then undersaturation of strangeness content

1) 0 + 0 -

2)

3)

<K > <K >, <K > <K due to isospin symm.

empirical factor < > 0.6 < >

from hadron gas model if not measured

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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)

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Energy dependence - average transverse mass

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

NA49 preliminary

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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More realistic model with initial QGP phaseY.Hama et al., Braz.J.Phys,34,322 (2004)

• hydrodynamic evolution in QGP and hadronic phases (SPheRIO)• NeXus type initial conditions at t0 = 1 fm/c (T0 = 135 → 265 MeV, ε0 = 1.4 → 11.4 GeV/fm3 at SPS)

describes the rise of pion multiplicity and saturation of T* for Kaons

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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hypothetical trajectories in the phase diagram

large (event-by-event) fluctuations are expected when the system hadronises close to the predicted critical point

(Lattice-QCD phase boundary: Fodor,Katz JHEP04(2004)050)

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

max.likelihood fit for each event

NA49 preliminary

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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The Event-by-Event (p + p)/π ratioB

eam

Ene

rgy

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

NA49 preliminary

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

( C.Alt et al., nucl-ex/0406013 )

-0.6< y <2.4

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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 :

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

σ/σT ≈ 10 – 35 %

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Λ elliptic flow (preliminary)• event plane from pions • flattening of acceptance via event plane shifting technique• correction for event plane resolution

• dE/dx identification of Λ decay daughters• Λ signal/background 5 - 11

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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v2(pT) at SPS and RHIC

increase of integrated v2 mainly due to increase of yield at large pT

Λ

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Conclusion from the energy scan at the SPS

• striking changes of energy dependence in 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 convincing anomalies in e-by-e fluctuations (K/π, charge), BE correlations and flow• reaction scenario with onset of deconfinement at the SPS provides a consistent explanation of the energy scan results

SPS energy range remains an interesting region for further study: • role of nuclear size (volume) in the onset of deconfinement • search for indications of the predicted critical point

→ Initiatives at the SPS, RHIC “fixed target”, CBM at GSI

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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The NA49 collaboration

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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blast-wave fit for a hadron resonance gas

(procedure of B.Tomasik nucl-th/0304079)

pions Kaons protons

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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energy dependence of Tf, βT

Blast wave fit for a resonance gas of π, K, p : kinetic freezeout temperature Tf , flow velocity βT

Tch

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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the energy dependence of the K/π ratios at midrapidity shows similar structure as the 4π results !

at midrapidity identification is from dE/dx and TOF

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Excitation functions of 4π yields compared to model predictions

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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Multiplicity fluctuations at 158A GeV (preliminary)

(NA49 preliminary)

small correction δ ≈ 10-2 forfluctuation in proj. participants:

selected range: 4 < y < 5.5

width increases with energy !

maximum of fluctuations at Npart ≈ 70

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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dependence on acceptance :NA49 preliminary

• fluctuations increase linearly with acceptance p = <Nacc>/<N4π>

• all charged >> negatives, positives

extrapolation to 4π :

no plausible explanation yet

P.Seyboth: Indications for the Onset of Deconfinement from NA49 21st Workshop on Nuclear Dynamics, Breckenridge, 5-12 February 2005

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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

Similar centrality dependence as Nch fluctuations

Correlation of <pT> with <Nch> due to energy conservation as in p+p ?(Mrowczynski,Rybczynski,Wlodarczyk nucl-th/040712)