Transcript Florenz 2006 - Gruppo1

Longitudinal Flow and
Onset of Deconfinement
Marcus Bleicher
Institut für Theoretische Physik
Goethe Universität Frankfurt
Germany
Marcus Bleicher, Florence 2006
Outline of the talk
• Introduction
• Fluctuations  Evidence for mixing
• Rapidity widths + Landau  softest point
• Summary
Marcus Bleicher, Florence 2006
The tool: UrQMDv2.2
•
•
•
•
Non-equilibrium transport model
Hadrons and resonances
String excitation and fragmentation
Cross sections are parameterized
via AQM or calculated by detailed balance
• pQCD hard scattering at high energies
• Generates full space-time dynamics of hadrons
and strings
Marcus Bleicher, Florence 2006
Thanks to the UrQMD group
@ Frankfurt
• Sascha Vogel (Resonances)
• Stephane Haussler (Event-by-Event Fluctuations)
• Hannah Petersen (Flow at FAIR)
• Diana Schumacher (Di-Leptons)
• Qingfeng Li (Isospin Dynamics & HBT)
• Xianglei Zhu (Elliptic Flow and Charm)
• Mohamed Abdel-Aziz (Event-by-Event Fluctuations)
• Elena Bratkovskaya (HSD)
• and Horst Stoecker (keeping it running)
Marcus Bleicher, Florence 2006
Motivation
At RHIC:
look for signals of
freely moving partons.
At FAIR/SPS:
look for the mixed
phase and the onset of
deconfinement
E. Bratkovskaya, M.Bleicher. et al., PRC 2005
Marcus Bleicher, Florence 2006
Excitation
functions: ratios
• ‘Horn’ in the K  /   ratio
not reproduced
•
K / 
well reproduced
•  /  relative strange baryon
enhancement reproduced
E. Bratkovskaya, M.Bleicher. et al., PRC 2005
Marcus Bleicher, Florence 2006
NA49 Preliminary
NA49 Preliminary
• K/ fluctuations increase towards lower beam energy
– Significant enhancement over hadronic cascade model
• p/ fluctuations are negative
– indicates a strong contribution from resonance decays
Marcus Bleicher, Florence 2006
Taken from Christoph Roland
Fluctuation studies
Energy dependence
• Qualitative description OK
• Importance of potentials at
low energies
• Lack of pressure shows up
at SPS energies
• EoS <-> Flow
H. Petersen, X. Zhu, M.B.
Marcus Bleicher, Florence 2006
‘Partonic’ dof already at
low SPS energy
•Breakdown of v2 in model
coincides with onset of
‘partonic’ matter
30 AGeV
 signals onset of change of
EoS in the early stage
H. Petersen, X. Zhu, M.B.
Marcus Bleicher, Florence 2006
UrQMD vs data
Pb+Pb/Au+Au
Stopping
power
• Linear increase of
rapidity shift at low
energies
• ‘Saturation’ above
highest SPS energy
• However, relative
momentum loss is
energy independent
Marcus Bleicher, Florence 2006
•
•
•
•
Multiplicities
Temperatures
Elliptic Flow
Correlations
have already been studied
Can we learn more from the
longitudinal dynamics?
Marcus Bleicher, Florence 2006
Multiplicity fluctuations
Pb+Pb (158 AGeV)
Extraction of the multiplicity distribution for every Npar
in the NA49 acceptance
(1.1<yCM<2.9)
Note: Calculation is narrower than the data for Npar~45
Marcus Bleicher, Florence 2006
Multiplicity fluctuations at SPS:
The problem
• The fluctuation is quantified with the
scaled variance :
Var(N) N 2  N

2
Var(N)
N
• Enhanced fluctuations for midperipheral collisions are observed
Similar results from HIJING, HSD
and RQMD
Note : - for a poisson distribution, w=1
Marcus Bleicher, Florence 2006
Where is the problem?
Pb+Pb (158 AGeV)
• Mean value correctly reproduced
in the NA49 acceptance
(1.1<yCM<2.9)
• Variance reproduced for central and very peripheral events
• Failure for mid-peripheral events
Marcus Bleicher, Florence 2006
Analysis of different windows
the normalized variance :
• flat in the projectile hemisphere
• larger in the mirror acceptance
• even larger in 4
• maximum around Np=40
Konchakovski, Haussler,…, PRC 73 (2006)
Marcus Bleicher, Florence 2006
Fluctutions in target region
• the fluctuation has a maximum
around Np=25
• introduces an asymetry between
projectile and target participants
• leads to an increase of the multiplicity
fluctuation in the target hemisphere

t arg
P
arg
Var(N tpart
)

t arg
N part
Marcus Bleicher, Florence 2006
Correlation length in rapidity
Rapidity window dependence :
• correlation length of the order of 1
unit of rapidity
• target and projectile hemisphere are
independent in hadron-string models
Marcus Bleicher, Florence 2006
Mixing and fluctuations
• I.e. the trigger condition ‘marks’
projectile and target participants
• This allows to study the degree of
mixing of the matter produced in HIC
• Data suggest strong mixing of
hemispheres
Hints to expanding initial fireball
in contrast to string dynamics
M. Gazdzicki and M. Gorenstein:
arXiv:hep-ph/0511058
Marcus Bleicher, Florence 2006
What the fluctuations told us…
• Initial fireball of newly produced particles
• Fireball seems to expand Landau-like
• Leads to strong correlations in rapidity
We might use Landau-type hydro to
explore the properties of this matter
Marcus Bleicher, Florence 2006
Pion rapidity density
• Pions rapidity
densities are
Gaussians at
all energies
D. Ouerdane, QM04
Marcus Bleicher, Florence 2006
Different particle types
• NA49 data yields
Gaussian rapidity
distributions
• Also ALL other
experiments report
Gaussians for
newly produced
particles
Marcus Bleicher, Florence 2006
Fireball expansion
• Assumptions:
- applies only to newly
produced particles
- Lorentz contracted
nuclei
E. Shuryak, Yad. Fiz. 16 (1972) 395
similar to Landau hydro
- simplified Hagedorn
gas EoS
For more praise on Landau hydro
see. P. Steinberg
Marcus Bleicher, Florence 2006
Rapidity widths
• Rapidity
width scales
linearly with
projectile
rapidity
M. Bleicher, hep-ph/0509314
Marcus Bleicher, Florence 2006
Speed of sound
• Analysis of the
rapidity data
indicates a
softest point at
20-30 AGeV
beam energy
M. Bleicher, hep-ph/0509314
Marcus Bleicher, Florence 2006
Its soft, but…
• …is it the mixed
phase?
• UrQMD also
describes the
rapidity widths
• UrQMD has a
soft equation of
state
Marcus Bleicher, Florence 2006
Summary
• Fluctuations indicate strongly mixed initial stage
• Assumption of Landau-type hydro allows to extract
speed of sound from rapidity widths
• Apparent local minimum of sound velocity
around 20 – 30 AGeV
• Nature of this softest point is unclear
Marcus Bleicher, Florence 2006