Strangeness Production and Thermal Statistical Model Huan Zhong Huang Department of Physics and Astronomy University of California, Los Angeles Department.
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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 interactionElectromagnetic interaction – photons infinite range -- photon masslessNuclear Interaction (Strong Force) – mesons Range (Rutherford Scattering) ~ 1-2 fmUncertainty principle
E t ~ cmeson mass ~ 100-200 MeV/c2
1937 Cloud Chamber cosmic ray eventsmass 106 MeV/c2
not the Yukawa meson, muon1947 C. Powell, C. Lattes and G. Occhialini
photographic plates at a mountain topm ~ 140 MeV/c2
+v
Particle Discovery
neutral pion 0 1950 accelerator experiment1947 G.D. Rochester and C.C. Butler
v – decay vertex – discovery
V0
V+
m ~ 1000 me
Kaon versus pion
du dduu 2
1Pions: ud
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
222 pNN mmEms
In Strong Interaction: strange quarks can only be produced in pairs !
Associated Production:p + N NK+
Pair Production:p + N pNK+K-
Threshold in fixed target: s = (E+mN)2 – p2
KKNppNNth
KNpNNth
mmmmmmmE
mmmmmmE
22
22
2
2
Associated Production More Effective (lower Threshold) @ low beam energies
The Melting of Quarks and Gluons-- Quark-Gluon Plasma --
Matter Compression: Vacuum Heating:
High Baryon Density-- low energy heavy ion collisions-- neutron starquark star
High Temperature Vacuum -- high energy heavy ion collisions -- the Big Bang
Deconfinement
Large to p Ratio
Anti-hyperon absorption in dense medium?
Dynamical conversion of anti-protons to anti-Lambda?
Similar results from E917.
E864/E878
Strangeness is ‘enhanced’ at SPS
No of Wounded Nucleons
YieldN-wound
Baryon and anti-baryons are both enhanced, but by different amount !
WA97/NA57 and NA49 Consistent Results
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 !!
Scenarios of Baryon Number Transport
Direct Transport Through Gluon Junctions …
X)
Indirect Transport Through Pair Production Modified by Baryon Chemical Potential …
and K
and K
and 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 !
Cannot Simply Blame Gluon Fragmentation !
Glu
on/Q
uar
k
~10-20% difference in baryon production between gluon and quark jets
(SLD)
1/3
String Fragmentations Suppress Strange Baryons
Standard string fragmentation for baryon formation through diquark tunneling out of string potential: dependence m(ud-1) = 0.49 GeV m(ud-0) = 0.42 GeV predicts =0.35.
If , STAR data would imply , very unlikely !
RQMD
Diquark fragmentation scheme for multi-strange baryon production in A+A collisions – Ruled Out ?!
See M.Bleicher et al, PRL 88, 202501 (2002) on Discussion,
/2me
Multi-parton Dynamics and Baryon Production
q
q
q q
Baryon Anti-Baryon
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: 0/ 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
Junction
Thermal Statistical Model
ch
i
ch
iT
n
T
n
nsi
chi T
mK
T
meeg
Tn ch
ss
ch
s2
2
2
3
2
ezdzn
nzK
n
zn
n
n
21
221
)!2(
!2)(
Particle Density
Modified Bessel Function
Must Include all particles including resonances !!Physical meaning of s – phase space suppresion factor
Misleadingly Appealing and Beautiful
Becattini: T=170, s=1
PBM (PLB518,(2000)41) predicts y=0ratios almost exactlyK-/K+=exp(2ms/T)(pbar/p)1/3
K- /K+=(pbar/p)1/4 is a fit to the data points
Agreement Appealing !Conceptually ?Equalibrium in local spatial region --- ButMeasurement in rapidity bin -- Fireball emission region in pT-y.I. Bearden, BRAHMS
R
s
R
s
Blast Wave
tanh 1 rE.Schnedermann et al, PRC48 (1993) 2462
dn
mT dmT r dr mT K1
mT coshT
0
R
I0pT sinh T
where:
r =s (r/R)n
STAR Preliminary
Different Freeze-out Conditions
Multi-strange Baryons freeze-out early: high T and small v
Physical origin for non-zero v?
/
p/K/
Strange Baryon Physics1 is special –
@AGS Quark level clustering or coalescence@SPS Sensitive to dynamics of baryon number transport@RHIC v2 and transverse radial flow reflects partonic
collectivityThere may be a special di-Omega state -]
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.
Statistical QCDStatistical QCD
42
228
72
30TQED
42
33228
783
30TQCD
photon spin electrons spin
gluon spin, color quarks spin, color, flavor
Energy density reflects the information on what the matter is made of !
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