Resonances in Heavy Ion Collisions
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Zhangbu Xu (BNL) SQM2003 1
Resonances in Heavy Ion Collisions
• Introduction– History/Techniques
• Particle Yield– Thermal Description– Strangeness Enhancement
• In-medium Effect• Time Scale Measurement• pT Spectra
– Flow Effect– High pT Phenomenon
O. Barannikova, M. Bleicher, G. Brown, P. Fachini, L. Gaudichet, T. Hallman,H. Huang, F. Laue, H. Long, R. Longacre, J. Ma, C. Markert , S. Salur, J. Sandweiss, E. Shuryak, A. Tai, G. Torrieri, T. Ullrich, N. Xu, E. Yamamoto, H. Zhang
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Zhangbu Xu (BNL) SQM2003 2
A little bit of historyWith the establishment of the hydrogen bubble-chamber, entirely new possibilities for research into high-energy physics present themselves. Results have already been apparent in the form of newly-discovered elementary particles. The first, very short-lived, so called, "resonance particle" was found in 1960. The Nobel Prize in Physics 1968
First time Invariant Mass was used (bump hunting)
(1952?)(1385) (1960)(892) (1961)(1405)
1411 (1967)
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Zhangbu Xu (BNL) SQM2003 3
Measurement Technique
• Mixed-event, Like-sign Background subtraction
• P-Wave Breit-Wigner function or Modified BWH. Zhang (STAR)
ISR STAR PreliminaryK*0 from p+p Collisions
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Zhangbu Xu (BNL) SQM2003 4
How Many Resonances?
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Zhangbu Xu (BNL) SQM2003 5
How are we doing so far?e+e-: 50 particlesAA: 16Including stable particles
How Many Measured?
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Experiments
Exp 2 4* 0 f0 4* 2* 4
NA49 1 1 1
NA50 1
PHENIX 2
STAR 1 4 1 1 4 2 2
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What do we do with it?
)/)(exp(
)/exp(22
2
uss
q
qihbind
mm
m
mMEi
Y.J. Pei, hep-ph/9610329
More advanced: Thermal model
e+e-
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Significance of Feeddown
0.18K 0.30
0 0.50
K* 0.60
1.00f0(980) 1.00
p, 0.20
++ 0.80
* 1.00
* 0.80
Hadron Primordial Fraction
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• Brown-Rho Scaling• Rho Broadening• Low Mass Dilepton
measuring properties
Last Call for RHIC PredictionsNucl.Phys. A661 (1999) 205-260
• Chiral UA(1) symmetry restoration (J. Schaffner, D. Kharzeev, et al.)
Medium Effect in Dense Nuclear Matter
R. Rapp, et al
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Zhangbu Xu (BNL) SQM2003 10
How to Probe Early Stage?
• Modification in medium
• Decay quicklymatter exists 10-23s
• Small or no FSIleptons, photons, neutrino
Golden: J/
q
q
l
l
s
Small Branching Ratio(10-4), Low Production Rate
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Zhangbu Xu (BNL) SQM2003 11
-Production: Hadronic versus Leptonic Decay Channel
• Different decay channels:– NA49: -+
– NA50: -+
• Transverse momentum spectrum– fit: 1/mTdn/dmT ~ exp(-mT/T)
(NA49: 3.0<y<3.8)
significant differences in slopes and yields
Dieter Röhrich, QM02
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Zhangbu Xu (BNL) SQM2003 12
Vector Meson at RHIC
• AMPT: (l+l-)/(K+K-)=1.5• Experiments’ comparison
c=50fm
K
K
l+l-
K+K-
AMPT, STAR
Nucl-th/0202086
130GeV
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hadronic/leptonic decay
)()(22.001.2dy
dN : 01.1
52.0 sysstatKK
PHENIX Preliminary
eeKK
PHENIX Preliminary
)()(5.24.5dy
dN : 4.3
8.2 sysstatee
e+e-
K+K-
200GeV
J. Nagle, QM02
Sensitivity Reach
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Dileptons at SPS
Conventional cocktail of particles Underpredicts dilepton production
Mass shifted??
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Last Call for RHIC PredictionsNucl.Phys. A661 (1999) 205-260
Cleaner Way of Detecting Modification?
Hadronic Decay at Late Stage
• Lower Density
• Lower Temperature
• Smaller Effect
• Hadronic Decay
• Larger Signal
• Extrapolation
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+ - Invariant Mass Distribution from Data at QM2002
• 2.1106 Au+Au minimum bias events and 4.7106 pp events
• Breit-Wigner fixed width 0 = 150 MeV and f0 = 75 MeV fixed f0 masse 0.98 GeV (AuAu) and 0.96 GeV (pp)
0 mass = 0.698 ± 0.013 GeV (AuAu)
0 mass = 0.729 ± 0.006 GeV (pp)
AuAu 40% to 80%0.2 pT 0.9
GeV/c
|y| 0.5
0
f0
K0S
K*0
STAR Preliminary
STAR Preliminary
0
f0
K0S
K*0
0.2 pT 0.8 GeV/c
|y| 0.5
pp
Statistical error only Statistical error only
sNN = 200 GeV
New: pT dependenceP. Fachinia (STAR)
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K*0 Mass and Width Distribution
K*0 Mass shift in p+p and Au+Au at low pT possible in-medium dynamiceffect modified K*0 mass and the line shape
K*0 width matches the MC prediction
STAR Preliminary
H. Zhang (STAR)
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What Effects?
• Rescattering
• Phase Space
• Interference
• Modification
Ron Longacre, et alWork in progress
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Zhangbu Xu (BNL) SQM2003 19
Probe Freeze-out Dynamics
Strange Hadron Resonances as a signature of freeze-out dynamics
hep-ph/0103149
Basic Idea:: Two parameters two measurements:
e-m/TSurviving possibility Thermal factor
e-t/c
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M. Bleicher QM02
Difference (t) may be SmallEffect is Large
Initial Production
Final Production
Transport ModelUrQMD
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All that Matters: X-section
Different by 5
Rescattering>Regeneration at later stage
Chemical freeze-out
Kinetic freeze-out
K*
lost
K*
measured
K
K* K
K*
K*
K
K*
K K K*
measured
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Yield and pT Spectra
STAR Preliminary
K*0/K in AuAu is a factor of 2 lowerthan in STAR pp rescattering
H. Zhang (STAR)J. Ma (STAR)
STAR Preliminary
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Flow/pQCD Effect
Gyulassy, etc.
Leading Quark Effect
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Particle Spectra
STAR Preliminary
T=156MeVpp: 63GeV
ISR Vector Mesons
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Zhangbu Xu (BNL) SQM2003 25
Power Law Spectra
mT-m0
STAR Preliminary
In AuAu Preliminary
In pp Preliminary
Power lawmT Exponential
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What Puzzles?
At pT ~ 2-3 GeV/c, yields approach each other. Heavier mass particles show stronger collective flow effects !
? When did the collectivity developed at RHIC
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Spectra Meet at 2GeV/c
130GeV
Proton Puzzle???
2GeV/c PUZZLE? dN/(dypTdpT)=constant |pT=2GeV/c
, different (rare particles)Low production Cross section Small Scattering X-sectionLess flow from hadronic stage???
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<p<pTT> centrality dependence> centrality dependence
1) , K, p mean transverse momentum <pT> increase in more central collisions;2) Heavier mass particle <pT> increase faster than lighter ones as expected from hydro type collective flow;
Star preliminary
1) , K, p mean transverse momentum <pT> increase in more central collisions;2) Heavier mass particle <pT> increase faster than lighter ones as expected from hydro type collective flow;3) -meson seems flow differently.
J. Ma (STAR)
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Zhangbu Xu (BNL) SQM2003 29
Resonance Elliptic Flow v2
Coordinate phase space
K*
K
K*
K
X
Y
Ky
x
py
Px
22
22
xy
xy )(tan,2cos 12
x
y
p
pv
(A.M.Poskanzer and S.A.Voloshin, Phys. Rev. C 58, 1671 (1998))
Coordinate-space-anisotropy Momentum-space-anisotropy
Momentum phase space
K*K*
K
X
Y
Nuclei Non-central Collisions Hot System Elliptic Shape
• partonic flow?
• Daughters re-scattering K*0
v2 sensitive to coordinate phase space
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Zhangbu Xu (BNL) SQM2003 30
K*0 , Elliptic Flow v2
Statistical error only
Statistical error only
STAR Preliminary
• Observed Significant K*0, Elliptic Flow v2 vs. Centrality and pT
• Need more statitics
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Zhangbu Xu (BNL) SQM2003 31
Summary
• Resonances are Important Tools in Heavy Ion Physics– Particle Production – Matter Properties (particle properties)– Hadronic Decay Probes Freeze-out Dynamics– Flow/High pT Effect
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More Conventional Approach
J. Kapusta QM02
CERES
Hadronic channels consistent??
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Zhangbu Xu (BNL) SQM2003 33
)1385(
)1520(
)(
)(
)(
0
0
'
0
*
pK
p
KK
N
K
K
S
Hadronic Decay Mode
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Zhangbu Xu (BNL) SQM2003 34
Statistical models
T. Ullrich QM02
Dieter Röhrich, QM02
Statistical Model: Work Reasonably wellMore Resonance Data Coming