Transcript Indications for the Onset of Deconfinement in Pb+Pb Collisions at the CERN SPS from NA49 P.Seyboth, MPI für Physik, Munich for the NA49

Indications for the Onset of Deconfinement in
Pb+Pb Collisions at the CERN SPS from NA49
P.Seyboth, MPI für Physik, Munich
for the NA49 collaboration
• Introduction
• Search for structure in the energy dependence of
– Inclusive particle production
– E-by-E fluctuations, BE correlations, flow
• Summary and conclusion
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
1
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)
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
2
The NA49 Detector
Target: 20cm liquid H2 or Pb foil
VCAL detects projectile spectators
Δp/p2 = 7 (0.3) • 10-4 (GeV/c)-1
(VTPC-1, VTPC+MTPC)
dE/dx resolution 3 – 6 %
TOF resolution ~ 60 ps
2,5 < p < 10 GeV :
TOF + dE/dx
at midrapidity
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
p > 7 GeV
dE/dx
forward rapidity
3
Pb+Pb collision at 158A GeV
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
4
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
Centrality
Event
Statistics
Taken 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
2002
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
PRC 66(2003)
054902
preliminary
5
Rapidity spectra
also: Ξ, Ω
Extrapolation
 4π yields
(open dots from reflection at ycm= 0)
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
6
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)
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
7
Transverse mass spectra at lower energy:
“blast wave” model describes spectra at all SPS energies
40A GeV
30A GeV
20A GeV
“kinetic” freeze out at T  120 –130 MeV, βT  0.4 – 0.5 at SPS
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
8
Particle yields – statistical model
(fits by F.Becattini et al, PRC69(2004)024905)
• 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
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
9
Particle yields at 40A, 80A GeV – statistical model
at lower energies μB increases, while T decreases slightly
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
10
Global view - Phase diagram
QGP
1st order
Hadrons
• 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 (Cleymans and Redlich,
PRL 81(1998) 5284 )
(Lattice-QCD phase boundary:
Fodor,Katz JHEP04(2004)050)
hadrochemical freeze out parameters
approach the phase boundary at SPS
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
11
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
    1.5  (       - )
particle species
 measure of entropy
in statistical models
SMES: statistical model of the
early stage
(Gazdzicki,Gorenstein :
Acta Phys.Pol. B30(1999)2705)
 s1/4
NN
Increase of initial d.o.f . g
between AGS and SPS ?
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
12
Energy dependence - ratio of K ,Λ yields to pions
• sharp peak of
K+/π+ ratio
• smooth rise of
anti-Λ/π
( s quarks)
hadronic models do
not (yet ?) reproduce
the sharp peak
• similar peak in
Λ/π ratio
• structure in K–/π–
( s quarks)
1
     (        )
2
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
13
Energy dependence – ratio of strange hadrons to pions
strangeness to pion ratio
peaks sharply at the SPS
partonic
mixed
partonic
hadronic
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
N N 
0.74 g s
ES  S S 
 
gu  gd  gg
1/4
 s NN
note :  K   2 ( K     K - )  4  K S0 

0.21
onset of deconfinement
at SPS ?
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
14
Energy dependence – inverse slope parameters
dN
- mT / T
 e
m T dm T dy
• inverse slope parameter T of K+ and K- constant at SPS
• 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 in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
15
Energy dependence - average transverse mass
Increase of <mT> for abundantly produced particles ( π, K, p)
slows sharply at the lowest SPS energy
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
16
The Event-by-Event K/π ratio
Beam Energy
max.likelihood fit for each event
σ2dyn = σ2data – σ2mixed
NA49 preliminary
Increased fluctuation signal at
lower beam energies
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
17
Beam Energy
The Event-by-Event p/π ratio
NA49 preliminary
The distribution of the E-by-E p/π ratio
is narrower for data than mixed events.
Effect of baryon resonance decay ?
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
18
Electric charge fluctuations
• Smaller in a QGP than in
a hadron gas
(Jeon,Koch,Asakawa,Heinz,Müller)
• Effect of hadronisation ?
 Z2 
q 
N
z q-q
z2
N
Z   (q i - q )
i 1
Central Pb+Pb collisions 158A GeV
 q ,GCC  1  N ch  /  N ch tot  1
Global charge conservation
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
19
Remove effect of global charge conservation :  q   q   q ,GCC
No clear energy dependence
of charge fluctuations at SPS
QGP signature possibly masked
by effect of resonance decays
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
20
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 in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
21
Anisotropic flow v2
Initial anisotropy ε in non-central collisions transformed into
momentum anisotropy v2 by pressure at early reaction stage
ε = (<y2>+<x2>)/(<y2>-<x2>)
SPS
RHIC
Smooth increase with collision energy towards
hydrodynamic model prediction
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
22
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
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
23
The NA49 collaboration
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
24
Extra slides for discussion
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
25
Estimate of initial energy density at 158A GeV
• from projectile energy loss and interaction volume:
  E / V  0.67  mN s NN
4
/   r03  A   1  13 GeV/fm 3
3
• from transverse energy production and Bjorken’s model:
NA49, PRL 75 (1995) 3814
  (dET / d ) /(  R 2  o )
 3.2 GeV/fm 3
with  0  1 fm/c
R  1.12  A1/3
initial energy density
ε > εc  1 GeV/fm3
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
26
Λ , Ξ and Ω rapidity spectra
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
27
Transverse mass spectra in p+p collisons at 158 GeV
“blast wave” model fit consistent with small βT
consistent with common temperature T  145 MeV
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
28
Statistical model for p+p collisions at 158 GeV
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
29
Energy dependence of K , Λ yields
 carriers of s quarks
 carriers of s quarks
    1.5  (        )
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
30
Energy dependence of total yield of s, s carriers
 carriers of s quarks
 carriers of s quarks
    1.5  (        )
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
31
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
32
System size dependence of strangeness production at
158A GeV
disappearance of
canonical suppression
for Npart > 60
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
33
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
34
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
35
Balance function for oppositely charged particles
158A GeV
(NA49 preliminary)
similar narrowing
at SPS and RHIC
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
36
Event-by-Event estimation of the particle ratios
One Event:
<dE/dx>
<dE/dx>
Event Ensemble:
log(Ptot [GeV])
Fit dE/dx spectra in 4D binning
<dE/dx>
log(Ptot [GeV])
• Vary relative normalization of the
particle species (K/,p/) in the
probability density function
• Extract ratios with maximum
likelihood fit
<dE/dx>
Probability density function:
log(Ptot
[GeV])Indications for the onset of deconfinement in
P.Seyboth:
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
37
v2(pT) at SPS and RHIC
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
38
Fluctuations of <pT> vs system size at 158A GeV
selected range: 4.0 < yπ< 5.5
corrected for limited 2-track resolution
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
39
Fluctuations of <n-> vs system size at 158A GeV
selected range: 4 < y < 5.5
correction for fluct. in
projectile participants:
(NA49 preliminary)
P.Seyboth: Indications for the onset of deconfinement in
Pb+Pb collisions at the CERN SPS from NA49 (ISMD2004)
40
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 (ISMD2004)
41