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Strangeness Production and Thermal Statistical Model. Huan Zhong Huang Department of Physics and Astronomy University of California, Los Angeles Department of Engineering Physics Tsinghua University. Strange Particle Discovery. 1935 Yukawa: meson exchange model for nuclear interaction

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Strangeness production and thermal statistical model

Strangeness Production and Thermal Statistical Model

Huan Zhong Huang

Department of Physics and Astronomy

University of California, Los Angeles

Department of Engineering Physics

Tsinghua University

Strange particle discovery
Strange Particle Discovery

1935 Yukawa: meson exchange model for nuclear interaction

Electromagnetic interaction – photons

infinite range -- photon massless

Nuclear Interaction (Strong Force) – mesons

Range (Rutherford Scattering) ~ 1-2 fm

Uncertainty principle

DE Dt ~ hc

meson mass ~ 100-200 MeV/c2

1937 Cloud Chamber  cosmic ray eventsmass 106 MeV/c2

not the Yukawa meson, muon

1947 C. Powell, C. Lattes and G. Occhialini

photographic plates at a mountain top

mp ~ 140 MeV/c2


Particle discovery
Particle Discovery

neutral pion p0gg 1950 accelerator experiment

1947 G.D. Rochester and C.C. Butler

v – decay vertex – discovery




m ~ 1000 me




Kaon versus pion
Kaon versus pion

Pions: p+p0p-

Neutron pions – the anti-particle is itself !!

not true to neutral K0

K0 and K0 are different particles !

u, d quark masses 5-10 MeV/c2

strange quark mass ~ 150 MeV/c2

SU(3) representation for u,d,s quarks, light quarks

Strangeness conservation
Strangeness Conservation

In Strong Interaction:

strange quarks can only be produced in pairs !

Associated Production:

p + N  NLK+

Pair Production:

p + N pNK+K-

Threshold in fixed target:

s = (E+mN)2 – p2

Associated Production More Effective (lower Threshold)

@ low beam energies

Strangeness production and thermal statistical model

The Melting of Quarks and Gluons-- Quark-Gluon Plasma --

Matter Compression: Vacuum Heating:


High Temperature Vacuum

-- high energy heavy ion collisions

-- the Big Bang

High Baryon Density

-- low energy heavy ion collisions

-- neutron starquark star

High baryon density at the ags
High Baryon Density at the AGS


14.6 A GeV


14.6 A GeV


11.7 A GeV


Yang Pang

Systematic kaon measurement
Systematic Kaon Measurement









L measurement
L Measurement

~ 17 Ls

per central



Large l to p ratio
Large L to p Ratio



absorption in

dense medium?


conversion of

anti-protons to


Similar results

from E917.

Strangeness is enhanced at sps
Strangeness is ‘enhanced’ at SPS

WA97/NA57 and NA49 Consistent Results



No of Wounded Nucleons

Baryon and anti-baryons are both enhanced, but by different amount !

Npart or no wounded nucleons
NPART or No Wounded Nucleons

Nucleons wounded once, twice or n times are different !

NA49 Data


Beam target fragmentation important
Beam-Target Fragmentation Important

E910 p+A @ AGS

Strange Baryon Production Increases with Number of Collisions !

NA49 results lead to the same conclusion for p+A collisions !

Both fragmentation and pair production increase @SPS !!

Proton fragmentation and hyperon production
Proton Fragmentation and Hyperon Production

E941@AGS data

Baryons Very Brittle!



4 p integrated ratio versus energy
4p Integrated Ratio versus Energy

Quark to pion ratio
Quark to Pion Ratio

Kink or Not ?

The w to w ratio


Pb+Pb @SPS

Many more Ws

Than Ws !!

The W to W Ratio

Scenarios of baryon number transport
Scenarios of Baryon Number Transport

Direct Transport Through Gluon Junctions …

W + K + K + K + (X)

Indirect Transport Through Pair Production Modified by

Baryon Chemical Potential …

  • W and W X K

  • X and X (L / S) K

  • L and L (p / n ) K

Net Baryon Density Increases the

Associated Production and

Transfers net baryon number

to multiply-strange baryons !

Event-by-Event STAR Hyperon Correlations

Doable with STAR TOF and SVT Upgrade !

Too many baryons at intermediate p t

Au+Au 0-10%


Too Many Baryons at Intermediate pT

Cannot simply blame gluon fragmentation
Cannot Simply Blame Gluon Fragmentation !



~10-20% difference in baryon production between gluon and quark jets

String fragmentations suppress strange baryons
String Fragmentations Suppress Strange Baryons

Standard string fragmentation for

baryon formation through diquark

tunneling out of string potential:


m(ud-1) = 0.49 GeV

m(ud-0) = 0.42 GeV

predicts S=0.35L.

If S=0.35L, STAR data

would imply X ~> S ,

very unlikely !





Diquark fragmentation scheme for multi-strange baryon production

in A+A collisions – Ruled Out ?!

See M.Bleicher et al, PRL 88, 202501 (2002) on W Discussion,

Multi parton dynamics and baryon production









Multi-parton Dynamics and Baryon Production

Baryon (Hyperon) Production may be Enhanced by

Multi-parton Dynamics:

Gluon Junction Mechanism -- (Kharzeev, Gyulassy and Vance ….)


Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al,

Molnar+Voloshin …..)

Quark Recombination – (R.J. Fries et al….)

Key Measurement: S0/L Ratio  0.35 String Fragmentation

 0.65-0.75 Thermal Statistical

 1 Gluon Junction/Coalescence

Physics Implication of multi-parton dynamics on v2 and RAA

Thermal statistical model
Thermal Statistical Model

Particle Density

Modified Bessel Function

Must Include all particles including resonances !!

Physical meaning of gs – phase space suppresion factor

Misleadingly appealing and beautiful
Misleadingly Appealing and Beautiful

Becattini: T=170, gs=1

PBM (PLB518,(2000)41) predicts y=0

ratios almost exactly



K- /K+=(pbar/p)1/4 is

a fit to the data points

Agreement Appealing !

Conceptually ?

Equalibrium in local

spatial region --- But

Measurement in rapidity

bin -- Fireball emission

region in pT-y.

I. Bearden, BRAHMS

Strangeness production and thermal statistical model

Blast Wave


E.Schnedermann et al, PRC48 (1993) 2462

r =s(r/R)n

STAR Preliminary

Blast wave fit
Blast Wave Fit

Parameters: Freeze-out T; Transverse Flow Velocity bT

Different freeze out conditions
Different Freeze-out Conditions



Multi-strange Baryons

freeze-out early:

high T and small v

Physical origin for

non-zero v?

Strange baryon physics
Strange Baryon Physics

  • Wis special –

  • @AGS  Quark level clustering or coalescence

  • @SPS  Sensitive to dynamics of baryon number transport

  • @RHIC  v2 and transverse radial flow reflects partonic

  • collectivity

  • There may be a special di-Omega state [W-W] !

  • 2) Baryons, Strange Hyperons, --

  • Multi-parton Dynamics: Gluon Junctions, Quark Coalescence

  • Quark Recombinations ……

  • We began to investigate quantitatively features which may

  • be related to anisotropy and hadronization properties

  • of bulk partonic matter !

  • 3) Strange Baryons and Heavy Quarks Are Sensitive Probes of Bulk

  • Properties of Matter at RHIC !

  • STAR’s future Barrel TOF and MicroVertex detector upgrade will

  • greatly enhance STAR’s physics capability on these topics.

Strangeness production and thermal statistical model

Statistical QCD

photon spin electrons spin

gluon spin, color quarks spin, color, flavor

Energy density reflects the information on what the matter is made of !

Strange baryons and dynamics of early stages
Strange Baryons and Dynamics of Early Stages

Precision Measurement of X and W Spectra Shape

at the Low pT Region is Needed !!

Javier Castillo