Mixed Hadron Ratios from STAR

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

mid-rapidity y=

/ K / p - slope parameters

dE/dx-analysis with TPC dE/dx , kink, V0 analysis comparisonfor charged and neutral Kaons

Slope Parameters via V0 PID (y=

Larger pt-range than dE/dx, better characterization of flow

Preliminarypt = 0.5-3.5 GeV/c

STAR B/B RatiosRatio approaching

1.0 as strangeness

content increases

Ratios calculated for central events at mid-rapidity, averaged over experimental acceptance in pt.With the assumption of equal acceptance of particle and antiparticle no corrections have to be applied

STAR preliminary

0.94

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)

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

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

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

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

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 ?

Implications for ratios

s (GeV)

(PRELIMINARY)

STAR 130 GeV14% central (

(*0.2)


Statistical errors only

Mid-rapidity ratios

Implications for ratios

s (GeV)(PRELIMINARY)


(PRELIMINARY)


(*0.2)



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

Sensitivity to multi-strange baryons

T (MeV)

Rat

ios

Model gets K-/,/- correct, butmisses on ratios!!!


+/

(Preliminary)

STAR 130 GeV14% central data

-/K-


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


Will change slightly with feeddown corrections (not included here)

STAR Preliminary

0

0.005

0.01

0.015

0.02130 GeV


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

Large ratio at AGS (and SPS) still not understood

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)


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


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.

•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 for Kaon and ratios which dominate strangeness production and seem to indicate strangeness saturation. These singly strange particles carry remnant quarks and/or valence di-quarks and are thus dependent on the baryochemical potential.

•The multistrange ratios still seem to indicate strangeness enhancement and are not described by the statistical models. This indicates an additional production mechanism which should be even stronger for the Omegas.

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Mixed Hadron Ratios from STAR