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

 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-- STAR @ RHIC High signal for the decay in KK, at the edge of the kinematically allowed region, rp decay suppressed

 mesons Features Information Quark Content : s sbar S = 0, Canonical suppression not applicable Meson Mass = 1.019 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- (~ 0.000299),  (~ 0.00025) ~ 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

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

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/0111159 Suppression causes : -Strangeness ordering -Beam energy dependence

 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:0804.4363 : 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 ?

 Production from KK Coalescence Naively from KK Coalescence RMS rapidity dist. STAR : Phys. Rev. Lett. 99 (2007) 112301 Phys. Lett. B 612 (2005) 181 NA49 : arXiv:0806.1937 Phys. Rev. Lett. 96 (2005) 052301 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

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/9907059 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

 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

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

Partonic collectivity at RHIC STAR : Phys. Rev. Lett. 99 (2007) 112301 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

 possibly decouples early arXiv:nucl-th/0606044 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/0509061 STAR : Nucl. Phys. A 757 (2005) 102 decouples from the system early at RHIC energies

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) 112301 arXiv: nucl-th:0406072

 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

 : 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

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

 : 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

High pT  probing partonic matter STAR : Phys. Rev. Lett. 99 (2007) 112301 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:0705.0953

 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

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:0705.0953 dAu collisions : Cronin Effect arXiv:hep-ex/0606049

 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