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PID spectra in STAR Baryon/anti-baryon ratios Mixed hadron ratios
Statistical models Chemical fits Quark coalescence Sudden hadronization Dynamical models
Conclusions
Rene Bellwied, Wayne State University, for the STAR Collaboration
Mixed Hadron Ratios from STAR
Mixed Hadron Ratios in year-1
• Particle Identification Methods
• Topology Analysis (V0’s)
• dE/dx in TPC (,K,p)
• Advanced Topology (kinks for K
• Mixed event method (resonances, V0’s)
• Corrected Spectra as a function of
• Centrality
• Rapidity
• Transverse Momentum or Mass
June 25, 2000
Rene Bellwied
Geometry Trigger and Multiplicity Cuts
Data Summer 2000 2.0 M total trigger events taken, 844 K central (top 15%) 331 K good (top 5%) central for physics analysis 458 K good min bias events for physics analysis
5% Central
Reconstructed vertex events nch - number of primary tracks in || < 0.75
~ 90% of all hadronic Au+Au interactions
central collisions
Particle Identification in TPC and RICH
Time Projection Chamber dE/dx below 1 GeV/c
Preliminary
Preliminary
Ring Imaging Cherenkov Detector Cherenkov angles at higher momenta
T = 190 MeV
T = 300 MeV
Tp = 565 MeV
mid-rapidity y=
Increase with collision centrality
consistent with Radial Flow
Slope Parameters via dE/dx PID
Particle Identification via Topology
Decay vertices
Ks + + -
p + -
p + +
- + -
+ + +
+ K -
“kinks”:
K +
Vo
Slope Parameters via V0 PID (y=
Larger pt-range than dE/dx, better characterization of flow
mt scaling depends on fit range
solid : used for fit
mT - m [GeV/c2]
1/m
T d
N/d
mT
(a
.u.)
K
p
STAR B/B Ratios
Ratio
approaching
1.0 as
strangeness
content
increases
Ratios calculated for central events at mid-rapidity, averaged over experimental acceptance in pt
STAR preliminary
Energy Evolution of B/B Ratio
STAR preliminary
Production of baryons through
pair processes increases dramati-
cally with s – still not baryon free
65.0
Trpair
pair
p
pbar
YY
Y
Y
Y
2Tr
pair
Y
Y
Pair-process production is larger than baryon transport
Note: 2/3 of protons from pair processes,
yet pt dist. the same as antiprotons
(ISR)
Mid-rapidity values for Central Collisions
Comparing RHIC(130 GeV) to SPS
K+/K- = 1.08 ±0.01 (stat.)±0.06
/h- = 0.021 ± 0.001 (stat.)±0.004
K*/h- = 0.06 ± 0.006 (stat.)±0.01
K*/h- = 0.058 ± 0.006 (stat.)±0.01
p/p = 0.6 0.02 (stat.) 0.06
¯/ = 0.73 ± 0.03 (stat.)
= 0.82 ± 0.08 (stat.)
¯
¯¯
Thermal Fit (prel.): T = 175 7 MeV, B = 50 6 MeV
Statistical models
Braun-Munzinger et al. (hep-ph/0106066)
- Follows curve for <E>/<N> = 1 GeV at freezeout
- Usesphenomenologicalparameterization:
B(s) 1.27 GeV
(1 s /(4.3 GeV)) J. Cleymans & K. Redlich,PRL 81 (1998) 5284
T and B according to thermal model
Assumption: strangeness in complete equilibrium i.e. strangeness saturation factor s = 1
Wroblewski factor evolution
Wroblewski factor dependent on T and B
dominated by Kaons
Peaks at 30 A GeV in AA collisions due to strong B dependence
mesons
baryons
hidden strangeness mesons
PBM et al., hep-ph/0106066
total
Strangeness production
Lines of constant S where:
<E>/<N> = 1 GeV
I. Increase instrange/non-strangeparticle ratios
II. Maximum isreached
III. Ratios decrease(Strange baryonsaffected more stronglythan strange mesons)Braun-Munzinger et al.
hep-ph/0106066
K/ ratio as a function of beam energy
saturation ?
K/ ratio as a function of beam energy
Experimental
4 yields
Strange Baryon production as a f(centrality)
Note: spectra are not feed-down corrected
yields are from fits to Boltzmann; h- yields are power law fits
STAR Preliminary
Conclusion:Strange baryon over charged particle ratio is constant
Saturation ?
Statistical model fit at 130 GeV
Chemical fit result
CentralChemical freeze-outparameters
Tch = 179±4 MeVB = 51±4 MeVs = -0.8±2.0 MeVs = 0.99 ±0.03
2/dof = 1.5
Ratio (data)
Rat
io (
chem
ical
fit
)
BRAHMSPHENIXPHOBOSSTAR
K /K
/
/
/p/p
K/h
K /h
Ks/h
K / K /
p/
p/
K/h
/h
/h
/h
/h
/h
Model: M.Kaneta, Thermal Fest (BNL, Jul 2001), N.Xu and M.Kaneta, nucl-ex/0104021
Implications for ratios
s (GeV)(PRELIMINARY)
STAR 130 GeV14% central (
(*0.2)
Braun-Munzinger et al.hep-ph/0106066
Statistical errors only
Mid-rapidity ratios
Sensitivity to multi-strange baryons
Stat. model can’t get a ratio above 0.09 in this phase space!
D. Magestroprivate communication
Implications for ratios
s (GeV)(PRELIMINARY)
STAR 130 GeV14% central (
(PRELIMINARY)
STAR 130 GeV14% central (
(*0.2)
Braun-Munzinger et al.hep-ph/0106066
Statistical errors only
Mid-rapidity ratios
Sensitivity to multi-strange baryons
T (MeV)
Rat
ios
Model gets K-/,/- correct, butmisses on ratios!!!
Statistical errors only
+/
(Preliminary)
STAR 130 GeV14% central data
-/K-
Braun-Munzinger et al.hep-ph/0105229
Thermal fit resultsin T = 174 MeV,B = 46 MeV.
Grand canonicalensemble, unlikeprevious model
Quark-Counting Ratios (ALCOR model)
*Duds
sdu*
s
s
u
u
uss
ssu
p
p*D
uud
duu
p
p*
s
s
u
u
uds
sdu Predict
Predict
su
su
K
K
s
s
u
uD Measur
e
Biro, Levai, Zimanyi: Phys. Lett. B347 (1995) p6
Assumption: formation of a constituent quark plasma with subsequent coalesence of the quarks into hadrons
Quark-Counting Ratios from STAR data
Quark-counting ratios are consistent with each other
Mea
sured
Predict
ed
Statistical errors only
Will change slightly with feeddown corrections (not included here)
STAR Preliminary
0
0.005
0.01
0.015
0.02130 GeV
Statistical errors only
STAR Preliminary14% central
Quark coalescence for mixed ratios
Quark coalescence (ALCOR)
Statistical model
Quark coalescence does better with
As B -> 0, sensitivity of the model to particle/antiparticle ratios is lost. Must look at ratios of dissimilar species to resolve model accuracy.
/p ratio correction factors
m =
m
pm = p+(0.64m+)
p + 0.88 (p+1.01 (
pm/m = 0.74 + 0.73 p/(
p/(pm/m – 1.01
Sudden hadronization model (1999)
1.0
2.0
3.0
4.0
/ p
QGPSudden Hadronization
Model
J. Rafelski innucl-th/9907090
Model predicts “most (anti)baryons produced will carry strangeness.”
Sudden hadronization model (2001)
1.0
2.0
3.0
4.0
/ p
QGP SuddenHadronization Model
J. Rafelski inhep-ph/0111467
(Preliminary)STAR Data Data errors not
small enough to discriminate
Stat. model 200 GeV predictions
Becattini et al.PRC 64 (2001) 024901
B(s) 1.27 GeV(1 s /(4.3 GeV))
s (GeV) B(MeV)
130 40.7
200 26.7
Use parameterization:
Predicts~0.8
(Preliminary)
STAR 130 GeV minbias data
(CAUTION! Really for 4 ratios)
Statistical errors only
Stat. Model Predictions Revisited
Becattini et al.PRC 64 (2001) 024901
B(s) 1.27 GeV(1 s /(4.3 GeV))
s (GeV) B(MeV)
130 40.7
200 26.7
Use parameterization:
(Preliminary)
STAR 130 GeV Data
(CAUTION! Really for 4 ratios) Pretty close to prediction!
(Preliminary)
STAR 200 GeV minbias data
Statistical errors only
What about other models ?• The models that do well with the multi-strange baryon mixed ratios are models that assume a quark phase (ALCOR and Rafelski’s models)
•It seems that purely hadronic statistical models fail for the description of yield and mixed ratios of multi-strange baryons, which was also the case at SPS
•A transport model assuming an initial plasma phase is doing well at SPS energies (Bass and Dumitru, nucl-th/0001033) and should be tested at RHIC
•The HIJING model can describe the data at the SPS with a purely hadronic scenario if the following additions are applied:
• baryon junction stopping and pair production: HIJING-BB
• general cascade program (GCP) for hadronic rescattering: HIJING-BB + GCP
• transient fluctuating fields or color ropes: HIJING-BB + GCP + Ropes
Some Conclusions• Statistical models do well in describing anti-baryon over baryon ratios, which yields constraints on the thermal freeze-out temperature and the baryo-chemical potential. This also allows us to determine an expansion velocity in a dynamical picture (see Helen’s talk).
•They also do well in Kaon and ratios which seem to indicate strangeness saturation, whereas the multistrange ratios still seem to indicate strangeness enhancement. This could still be a QGP signature !
•the anti-/anti-p continues to drop from AGS to SPS to RHIC
•the baryon/meson ratio seems to increase as a function of pt
• OFF TO THE OMEGAS !!!
