Energy and system size dependence of strangeness production, from SPS to RHIC
Strangeness and bulk freeze-out properties at RHIC
description
Transcript of Strangeness and bulk freeze-out properties at RHIC
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24 June 2007
Strangeness in Quark Matter 2007
STARSTAR
2S0Q0M7
Strangeness and bulk freeze-out properties at RHIC
Aneta Iordanova
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Outline
Motivation STAR Experiment Analysis Techniques Results Summary
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Motivation
Identified particle spectra in heavy-ion collisions at different center-of-mass energies and system size provide a unique tool to explore the QCD phase diagram. system size dependence of the freeze-out parameters at RHIC.
Bulk properties: - Kinetic freeze-out properties from spectral shapes
• Tkin at kinetic freeze-out, transverse radial flow (β) - Chemical freeze-out properties from particle ratios
• Tch at chemical freeze-out, strangeness and baryon production
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
STAR Experiment
Time Projection Chamber Measures charged particle
momenta and energy loss within ||<1
Full azimuthal acceptance
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Analysis Technique
Exploit the ionization energy loss (dE/dx)
Distribution is normalized by the theoretical expectation for different particle types; e.g.
z()=ln[(dE/dx)/(dE/dxTh)].
z() distribution is sliced into p=50MeV/c for
|y|<0.1 (mid-rapidity) 6 centrality bins - corresponding to
the top 60% of the cross-section. √sNN=62.4GeV and 200 GeV
Consistent analysis technique is used for all low pT measurements for different center-of-mass energies and colliding systems.
Raw yields are extracted for different particles from multi-Gaussian fits.
Cu+Cu 200 GeV0-10% central
0.50<pT<0.55 GeV/c
Cu+Cu 200 GeV
Minimum Bias
pion
kaon
electron
proton
normalized
STAR Preliminary
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Results – Particle Spectra
Raw data are corrected for: Single particle (track
finding) efficiency Energy Loss in the TPC Pions/protons corrected
for background
Corrected spectra are shown for mT-m0 Central 0-10% data Mass dependence is
observed in the slope of the spectra shapes
STAR Preliminary
10% central, Cu+Cu200 GeV62.4 GeV
–
–
p
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Results – Particle Ratios
K–/– ratio Systematically higher
in the smaller system p/– ratio
Same for Au+Au and Cu+Cu
STAR Preliminary
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Fitting the data – Statistical Model
The model has 4 fit parameters: chemical freeze-out
temperature, Tch baryon chemical
potential, μB strangeness chemical
potential, μS strangeness
suppression, γS
0)(
2
2 12),( TSBE
Ss
ii iSiBi
i
e
dppgTn
STAR Preliminary
10% central, Cu+Cu @ 62.4 GeV10% central, Cu+Cu @ 200 GeV
Fit uses only data from , K and p
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Chemical freeze-out properties
Strangeness suppression factor consistent within errors
with Au+Au results for the central data
But appears to be systematically higher for the smaller system
STAR Preliminary
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Chemical freeze-out properties
Chemical freeze-out temperature Universal chemical
freeze-out temperature, Tch, is observed for all studied systems.
5% central10% centralMin-Bias
STAR Preliminary
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Chemical freeze-out properties
Chemical freeze-out temperature Similar systematic
dependence is observed for different ion species as a function of centrality.
STAR Preliminary
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Fitting the data – Blast –wave model
The model assumes a boosted thermal source in transverse and longitudinal directions.
3 fit parameters are extracted: flow velocity, β kinetic freeze-out
temperature, Tkin
shape of the flow profile, n
(PR C48 (1993) 2462)
R r R
n
sr R
rrr
)()(
r 1tanh
kin
T
kin
TR
TTT T
mK
T
pIrdrm
dmm
dn coshsinh1
0
0
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Fit Results
Blast wave fits are performed in each centrality bin simultaneously for π±, K±, p and p-bar.
For the case of pions, the range below 0.5 GeV/c is excluded in order to reduce effects from resonance contributions.
10% central, Cu+Cu @ 62.4 GeV10% central, Cu+Cu @ 200 GeV
STAR Preliminary
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Particle mean-pT
Particle mean-pT:
increases with centrality (Nch). consistent with an increase in
radial flow with centrality.
Remarkable similarities as a function of Nch are observed.
for both Cu+Cu and Au+Au systems
at both center-of-mass energies, 200 and 62.4 GeV.
Are the bulk properties entropy driven? * Bose-Einstein fits over the entire fiducial spectra range are used for the case of pions.
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
STAR Preliminary
Kinetic freeze-out properties
All particle spectra for p±, K±, p and p-bar in Cu+Cu and Au+Au systems appear to be described by a common set of freeze-out parameters.
Cu+Cu 0-10% Au+Au 0-5%
Kinetic Parameters 62.4 GeV 200 GeV 62.4 GeV 200 GeV
flow velocity 0.48±0.06 0.52±0.07 0.54±0.01 0.59±0.05
Tkin (MeV) 115±7 112±9 93.8±4.1 89±12
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Kinetic freeze-out properties
STAR Preliminary STAR Preliminary
These extracted freeze-out parameters are found to be similar for an equivalent Nch
for both Cu+Cu and Au+Au systems at both center-of-mass energies, 200 and 62.4 GeV.
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STARSTAR
2S0Q0M7
24 June 2007Aneta IordanovaStrangeness in Quark Matter 2007
Summary
STAR has enlarged the variety of hadron spectra measurements at RHIC by providing new results for Cu+Cu at two different center-of-mass energies, √s=200 and 62.4 GeV.
Thermal models used for studying kinetic and chemical freeze-out properties point to a systematic dependence on the number of charged particles produced Independent of collision system and energy
This multi-dimensional systematic study has revealed the importance of the initial collision geometric overlap.