Transcript Strange Baryon Production at the AGS, SPS and RHIC

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
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
pm+v
Particle Discovery
neutral pion p0gg 1950 accelerator experiment
1947 G.D. Rochester and C.C. Butler
v – decay vertex – discovery
p
V0
+
pm ~ 1000 me
m+
V+
n
Kaon versus pion
1
uu + d d  p d u 
Pions: p u d 
p
2
+
0
-
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 Quark Mass Important!
SU(3) Representation of Particles
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
s  2 EmN + m N2 + m 2p
2 Eth m N + m N2 + m 2p  m N + mL + m K
2 Eth m N + m N2 + m 2p  m p + m N + m K + m K
Associated Production More Effective (lower Threshold)
@ low beam energies
Strange Baryons Sensitive to Bulk
Partonic Matter
Tc~ ms
The Melting of Quarks and Gluons
-- Quark-Gluon Plasma -Matter Compression:
Vacuum Heating:
Deconfinement
High Baryon Density
-- low energy heavy ion collisions
-- neutron starquark star
High Temperature Vacuum
-- high energy heavy ion collisions
-- the Big Bang
High Baryon Density at the AGS
Si+Si
14.6 A GeV
Si+Au
14.6 A GeV
Au+Au
11.7 A GeV
ARC
Yang Pang
Systematic Kaon Measurement
Au+Au
Si+Au
NK-
NK+/NK-
NK+
E802/E859/E866
NPart
NPart
L Measurement
~ 17 Ls
per central
Au+Au
@ AGS
Large L to p Ratio
E864/E878
Anti-hyperon
absorption in
dense medium?
Dynamical
conversion of
anti-protons to
anti-Lambda?
Similar results
from E917.
Strangeness is ‘enhanced’ at SPS
WA97/NA57 and NA49 Consistent Results
Yield
N-wound
No of Wounded Nucleons
Baryon and anti-baryons are both enhanced, but by different amount !
NPART or No Wounded Nucleons
Nucleons wounded once, twice or n times are different !
NA49 Data
NPart
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
E941@AGS data
pAup+X
pAun+X EQUAL
Baryons Very Brittle!
Energy Dependence of Strangeness Production
Mid-rapidity Ratio versus CM energy
4p Integrated Ratio versus Energy
s
1/4
NN
Strange Quark Production
Quark to Pion Ratio
Kink or Not ?
The W to W Ratio
@mid-rapidity
Pb+Pb @SPS
Many more Ws
Than Ws !!
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 W and W X K
X X and X L / S K
L 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 !
Multi-Strange Baryon Spectrum Shape
Too Many Baryons at Intermediate pT
Au+Au 0-10%
p+p
Cannot Simply Blame Gluon Fragmentation !
Gluon/Quark
(SLD)
~10-20% difference in baryon production between gluon and quark jets
String Fragmentations Suppress Strange Baryons
Standard string fragmentation for
baryon formation through diquark
tunneling out of string potential:
-pm2 / 
dependence
e
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 !
RQMD
L
1/3
S+ S- S0
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
Baryon (Hyperon) Production may be Enhanced by
Multi-parton Dynamics:
Gluon Junction Mechanism -- (Kharzeev, Gyulassy and Vance ….)
q
Junction
q
q
Anti-Baryon
Baryon
q
q
q
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
Particle Density
3
ch
2
T
ns
ni 
gig s e
2p
nq m q
Tch
Modified Bessel Function
n
e
ns m s
Tch

2
 mi 
 mi 

 K 2 

 Tch 
 Tch 

2 n! 1
2
2
K n ( z) 
d


z
n 
(2n)! z z
n- 1

2
e
-
Must Include all particles including resonances !!
Physical meaning of gs – phase space suppresion factor
Thermal Statistical Model
200 GeV
62.4 GeV
200 GeV
Tch (MeV)
160-170
 160-170
mB (MeV)
 70
 20
ms (MeV)
0
0
Strangeness Enhancement and gs
Chemical Freeze-out @ Phase Boundary
Misleadingly Appealing and Beautiful
Becattini: T=170, gs=1
PBM (PLB518,(2000)41)
predicts y=0
ratios almost exactly
K-/K+=
exp(2ms/T)(pbar/p)1/3
K- /K+=(pbar/p)1/4 is
a fit to the data points
I. Bearden, BRAHMS
Agreement Appealing !
Conceptually ?
Equalibrium in local
spatial region --- But
Measurement in rapidity
bin -- Fireball emission
region in pT-y.
Kinetic and Chemical Freezeout
Blast Wave
R
dn
mT cosh    pT sinh  

  r dr mT K1
I0

 
mT dmT 0
T
T 
where:
  tanh
-1
r
E.Schnedermann et al, PRC48 (1993) 2462
s
R
r =s (r/R)n
STAR Preliminary
Blast Wave Fit
Parameters: Freeze-out T; Transverse Flow Velocity T
Different Freeze-out Conditions
X/W
p/K/p
Multi-strange Baryons
freeze-out early:
high T and small v
Physical origin for
non-zero v?
Have We Observed This ?
Strange Baryon Physics
1 W is 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.
END of Talk
Statistical QCD
 QED
p2 
7
 4

2
+
2

2
T


30 
8

photon spin
 QCD
electrons spin
p 
7
 4

3  8 +  2  2  3  3T

30 
8

2
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
Precision Measurement of X and W Spectra Shape
at the Low pT Region is Needed !!
Javier Castillo