1. Strangeness Enhancement Partonic Collectivity Hints of Thermalization
Probe the QCD Phase Diagram with  mesons in High Energy Nuclear Collisions
Outline
 meson in high energy collisions
Strangeness Enhancement
Partonic Collectivity
Hints of Thermalization
Review of existing results
Probing QCD phase boundary
Low pT (< 3 GeV/c) :
v2 measurement
High pT (> 3 GeV/c) :
Nuclear Modification Factor

2.  mesons - Discovery
First seen in bubble chamber experiments at Brookhaven in 1962 in the reactions
K- + p  L + K+K
K- + p  L + K++K-
Mass 1020 MeV, G <<20 MeV
Quantum numbers JPC = 1--
RHIC
High signal for the decay in KK,
at the edge of the kinematically
allowed region, rp decay suppressed

3.  mesons Features Information Quark Content : s sbar
S = 0, Canonical suppression not applicable
Meson
Mass = GeV
Mass ~ lightest baryons - p,n,
Differentiates mass and constituent quark effects
Width = 4.43 MeV
Narrow - Experimentally Clean signal
Change in width can reflect medium effects
Decay modes
Primordial fraction
Both hadronic and leptonic : K+ K- (~ 49.1%), K0s K0L (~34.1%),  (~ 15.5%), e+e- (~ ),  (~ )
~ 100%
Small Interaction with nucleons. OZI rule
Life time ~ 45 fm/c
Early freeze-out. Could reflect collectivity at partonic level. Cronin effect ?
More than expected for partonic phase
With K* (~ 4 fm) ideal for studying re-scattering effects
Production Mechanism :
Lightest Vector Meson, j = 1, quark spins are parallel, orbital angular momentum zero
Difficult to produce due to OZI rule (QCD interpretation- production suppressed by S3)
QGP : partonic coalescence - Enhancement
Hadronic : Fusion of strange sea quarks of incoming nucleons
Secondary interactions Baryon-Baryon,
Kaon-hyperon and Kaon-anti-Kaon

4. Next :  meson and Strangeness Enhancement
Remark
Golden ratio
meson in high energy collisions
A golden tool which can be used to address
various aspect of heavy-ion collisions
Next :  meson and Strangeness Enhancement

5. Strangeness Enhancement
QGP scenario :
Phys. Rep. 88 (1982) 331
Phys. Rev. Lett. 48 (1982) 1066
Phys. Rep. 142 (1986) 167
Copious production of s sbar pairs
Strangeness enhancement relative to p+p collisions
Stronger effect for multi-strange hadrons and increases with strangeness content
Canonical Effect in p+p collisions : Quantum Numbers exactly conserved
Phys. Lett. B. 388 (1996) 401
Phys. Rev. C 58 (1997) 2747
Phys. Rev. C 57 (1998) 3319
Phys. Lett. B. 486 (2000) 61
Eur. Phys. J. C 24 (2002) 589
hep-ph/
Suppression causes :
-Strangeness ordering
-Beam energy
dependence

6.  mesons and Strangeness Enhancement
Strangeness enhancement observed
-- Dense medium formation in A+A ?
-- Canonical suppression in p+p ?
Statistical model predictions
-- Enhancement increases with strange-quark
content
-- Enhancement higher for lower beam energy
at RHIC energies:
-- Not canonically suppressed
-- Does not follow number of strange-quark
ordering
-- Enhancement(62.4) < Enhancement(200)
STAR Preliminary
enhancement between K-() and 
is not understood
STAR :arXiv:
: J.Phys.G35:044031,2008
Possible Issues :
If formed by KK coalescence can be subjected to Canonical suppression.
Is production OZI suppressed in p+p collisions ?

7.  Production from KK Coalescence
Naively from KK Coalescence
RMS rapidity dist.
STAR : Phys. Rev. Lett. 99 (2007)
Phys. Lett. B 612 (2005) 181
NA49 : arXiv:
Phys. Rev. Lett. 96 (2005)
If formed by KK Coalescence
-- K- ratio will change with collision centrality/Beam energy/System size
-- Width of rapidity distribution : 1/ ~ 1/K- + 1/K+
--- Inverse Slope of transverse momentum distribution : T~ 2 TK
--- Constraints due to the spin quantum number (K are spin 0 and is spin 1)
production likely not from KK coalescence at RHIC energies
Observed strangenessenhancement unlikely due to Canonical suppression effects

8. Okubo Zweig Iizuka Suppression of
Phys. Lett. 5 (1963) 165
CERN Report Nos. TH-401 and
TH-412 (1964) (unpublished)
Prog. Theor. Phys. 35 (1966) 1061
Violations of OZI rule observed
in p+p collisions.
s or c
f or J/y
OZI suppressed u d
 - + 0
Not OZI suppressed s f
K - K+
Phys. Lett. B 59 (1975) 88
arXiv: nucl-th/
R()=tan2()= 4.2 X10-3 : deviation from ideal mixing angle
Phys. Lett. B 60 (1976) 371
Phys. Lett. B 353 (1995) 319
Phys. Lett. B 592 (2004) 1
Suppression of interaction with nucleons,
non-strange mesons and resonances
High colliding energies at RHIC OZI suppression could be lifted : Observed enhancement unlikely due to OZI suppression in p+p collisions

9.  meson Strangeness Enhancement
Remark
Golden ratio
 meson in high energy collisions
A golden tool which can be used to address
various aspect of heavy-ion collisions
 meson Strangeness Enhancement
Strangeness enhancement in heavy-ion collisions at RHIC
possibly is due to formation of a dense medium and not due to
Canonical Suppression effects
Next meson - Partonic Collectivity and Thermalization

10. Initial spatial anisotropy
Collectivity
Initial spatial anisotropy
Pressure gradiant y  x
INPUT
dN/df f 2p
2v2
Spatial Anisotropy
dN/df  2p
Interaction among
produced particles
OUTPUT
Momentum Anisotropy

11. Partonic collectivity at RHIC
STAR : Phys. Rev. Lett. 99 (2007)
Substantial v2 measured for mesons
v2 similar to other mesons
Constituent Quark Scaling Observed
Reflects partonic collectivity :
Heavier s quarks flows
as lighter u and d quarks
To further strengthen the idea of partonic
collectivity
--not formed from KK coalescence (already discussed)
--  likely decouples early in interactions
and does not participate strongly in hadronic interactions

12.  possibly decouples early
arXiv:nucl-th/
STAR : Phys. Lett. B 612 (2005) 181
Au+Au
 <pT> is almost independent of centrality unlike anti-protons
Indicates possibly it decouples early in the interaction
~ 10 mb
~ 3 
~ 4 
~ 3.5 
~ 2.6 
~ 2.1 
frezee-out just after Tc from Lattice QCD at RHIC
No decay
b=2.0fm
Van Hecke, Sorge, Xu (98)
arXiv:nucl-th/
STAR : Nucl. Phys. A 757 (2005) 102
decouples from the system early at RHIC energies

13. Hints of Thermalization
Monotonic rise of  ratio at low pT
-- Good agreement with models based on  and production by thermal s-quark coalescence
Clear change in spectral shape
-- Exponential (~thermal) for central collisions
-- Power law type (~ hard process) at high pT in peripheral collisions
STAR : Phys. Rev. Lett. 99 (2007)
arXiv: nucl-th:

14.  meson Strangeness Enhancement
Remark
Golden ratio
 meson in high energy collisions
A golden tool which can be used to address
various aspect of heavy-ion collisions
 meson Strangeness Enhancement
Strangeness enhancement in heavy-ion collisions at RHIC
is due to formation of s dense medium and not due to
Canonical Suppression effects
 meson : Partonic Collectivity and Thermalization
The collectivity observed in heavy-ion collisions at RHIC
is developed at the partonic stage. Hints of formation
of some kind of thermalized (partial?) system
Next meson as a probe for QCD phase boundary

15.  : Probe QCD phase diagram
Supporting observations from previous
discussions -
-- Primordial production ~ 100%
- Decouples early from the system ~ TC
- Not formed from KK Coalescence
- Hadronic interactions small/OZI suppressed
-- ss structure and Strangeness enhancement
a dynamical effect
-- Substantial v2 observed in Au+Au 200 GeV
-- NCQ Scaling
Key observable : v2 of  meson
RHIC data suggests - collectivity observed in  due to partonic interactions
Absence/reduction of collectivity and NCQ scaling of  could indicate system in Hadronic phase

16. v2 expectation from AMPT
Default setting, ~ 10 mb
No NCQ Scaling observed
Large v2 ofcould bedue to KK contributions
Partonic Coalescence
NCQ scaling observed
By Wu Kejun

17.  : Probe QCD Phase Diagram - plan
Measure -v2 as a function of beam
energy and collision centrality
2. How to map to phase diagram :
Tch and B changes in beam energy and
collision centrality
3. Large v2 and NCQ scaling present
~ matter went through partonic phase
Small v2 and NCQ scaling broken
~ matter only went through hadronic phase
Example : Only v2 available in Heavy ion collisions is at Au+Au 200 GeV

18. High pT  probing partonic matter
STAR : Phys. Rev. Lett. 99 (2007)
STAR Preliminary
Observations :
Suppression in 200 GeV Au+Au collisions
No suppression in 200 GeV d+Au collisions
Interpretation :
Dense medium formed in 200 GeV Au+Au collisions
Turn-off of suppression may indicate hadronic matter
Advantage over other hadrons : Production likely via parton coalescence
Then will reflect gluon energy loss
arXiv:

19.  meson Strangeness Enhancement
Remark
Golden ratio
 meson in high energy collisions
A golden tool which can be used to address
various aspect of heavy-ion collisions
 meson Strangeness Enhancement
Strangeness enhancement in heavy-ion collisions at RHIC
is due to formation of a dense medium and not due to
Canonical Suppression effects
 meson : Partonic Collectivity and Thermalization
The collectivity observed in heavy-ion collisions at RHIC
is developed at the partonic stage. Hints of formation
of some kind of thermalized (partial?) system
 meson as a probe for QCD phase boundary
Large collectivity and Number of Constituent Quark Scaling
clear indication matter went through partonic phase

20. Summary Measurements Conclusions
Yield as a function of collision centrality and Beam Energy
Strangeness Enhancement at top RHIC energy due to dense medium formed in the collisions.
 enhancement at RHIC lying between K-() and  is not understood
Azimuthal Anisotropy Measurements
Partonic Coalescence, Significant Collectivity at Partonic Level
Spectra Shape and  ratio as a function of pT (< 2 GeV/c)
Comparison to models - Partonic Coalescence and hints of thermalization
Nuclear Modification Factor
Dense medium and Partonic coalescence
Production :/K ratio as a function of beam energy, Width of rapidity distribution, Slope of pT spectra
not likely from KK Coalescence at RHIC energies
<pT>, Spectra compared to hydrodynamical calculations, results from photo production
Early freeze out, close to transition temperature
Hadronic phase : No NCQ scaling, small v2
Partonic phase : NCQ scaling large v2
AA collisions : Gluon energy loss arXiv:
dAu collisions : Cronin Effect arXiv:hep-ex/

21.  b a Thanks to the Organizers and IAC for this opportunity -- Zweig
 p-p+p0 is suppressed compared to
K-K+ (which is actually kinematically suppressed)
"Feynman taught me that in strong interaction physics everything that can possibly happen does, and with maximum strength,Only conservation laws suppress reactions. Here was a reaction that was allowed but did not proceed.”
-- Zweig b
De Divina Proportione a
 The Golden Ratio is a universal law : in which is contained the ground-principle of all formative striving for beauty and completeness in the realms of both nature and art, and which permeates, as a paramount spiritual ideal, all structures, forms and proportions, whether cosmic or individual, organic or inorganic, acoustic or optical; which finds its fullest realization,
however, in the human form. -- Adolf Zeising
Thanks to the Organizers and IAC for this opportunity