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Indications for the Onset of Deconfinement in Pb+Pb collisions at the SPS. P.Seyboth, MPI f ür Physik, München for the NA49 Collaboration. Introduction Search for structure in the energy dependence of Inclusive particle yields E-by-E fluctuations: K/ π , Q BE correlations - PowerPoint PPT Presentation
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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
22
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)