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 mesons in High Energy Nuclear Collisions

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1  mesons in High Energy Nuclear Collisions
Bedanga Mohanty VECC, Kolkata Outline  meson in High Energy Collisions Strangeness Enhancement Partonic Collectivity Recombination and hints of Thermalization Review of existing results Probing QCD Phase Boundary  : v2 measurement Thanks to Nu Xu, Jinhui Chen, Zhangbu Xu, Huan Huang, Guoliang Ma and STAR for discussions QGP Meet 2008 : Bedanga Mohanty

2 QGP Meet 2008 : Bedanga Mohanty
 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, BNL High signal for the decay to KK, at the edge of the kinematically allowed region, rp decay suppressed STAR : QM2008 QGP Meet 2008 : Bedanga Mohanty

3 QGP Meet 2008 : Bedanga Mohanty
 mesons Features Information Quark Content : s sbar S = 0, No Canonical suppression, Strangeness Enhancement 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- (~ 49.2%), K0s K0L (~34.1%),  (~ 15.5%), e+e- (~ ),  (~ ) ~ 100%, little resonace contribution 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/c) 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, K-hyperon and K-anti-K QGP Meet 2008 : Bedanga Mohanty

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 QGP Meet 2008 : Bedanga Mohanty

5 Strangeness Enhancement
QGP scenario : Phys. Rep. 88 (1982) 331 Phys. Rev. Lett. 48 (1982) 1066 Phys. Rep. 142 (1986) 167 P. Koch, B. Muller,J. Rafelski Copious production of s and 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 Suppression causes : -Strangeness ordering -Beam energy dependence 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/ J. Cleymans, A. Muronga, K. Redlich, A. Tounsi, et al. QGP Meet 2008 : Bedanga Mohanty

6  mesons and Strangeness Enhancement
arXiv: Strangeness enhancement observed -- Dense partonic 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  ? 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 ? QGP Meet 2008 : Bedanga Mohanty

7  Production from KK Coalescence
Naively from KK Coalescence RMS rapidity dist. STAR : Phys. Rev. Lett. 99 (2007) Phys. Lett. B 612 (2005) 181 arXiv: 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 ---  and K v2 measurements (discussed later) --- Constraints due to the spin quantum number (K are spin 0 and is spin 1) production not from KK coalescence at RHIC energies Observed strangenessenhancement not 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 R()=tan2()= 4.2 X10-3 : deviation from ideal mixing angle Violations of OZI rule observed in p+p collisions. Phys. Lett. B 60 (1976) 371 Phys. Lett. B 353 (1995) 319 Phys. Lett. B 592 (2004) 1 Phys. Lett. B 59 (1975) 88 arXiv: nucl-th/ s or c f or J/y OZI suppressed u d  - + 0 Not OZI suppressed s f K - K+ Suppression of interaction with nucleons, non-strange mesons and resonances At high colliding energies at RHIC -- OZI suppression could be lifted Observed enhancement not 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 is due to formation of a dense partonic medium and not alone due to Canonical Suppression effects STAR Preliminary Next meson - Partonic Collectivity, Recombination and Thermalization QGP Meet 2008 : Bedanga Mohanty

10 Collectivity y  x 2v2 Initial spatial anisotropy Pressure gradiant
INPUT dN/df f 2p 2v2 Spatial Anisotropy dN/df 2p Interaction among produced particles OUTPUT Momentum Anisotropy QGP Meet 2008 : Bedanga Mohanty

11 Partonic collectivity at RHIC
STAR : Phys. Rev. Lett. 99 (2007) PHENIX : 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 QGP Meet 2008 : Bedanga Mohanty

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  decouples early in the interaction ~ 10 mb ~ 3  ~ 4  ~ 3.5  ~ 2.6  ~ 2.1  frezee-out at RHIC just after Tc from Lattice QCD STAR : Nucl. Phys. A 757 (2005) 102 arXiv:nucl-th/ No decay b=2.0fm Van Hecke, Sorge, Xu (98) decouples from the system early at RHIC energies

13 Recombination and Hints of Thermalization
STAR preliminary 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: arXiv: QGP Meet 2008 : Bedanga Mohanty

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 dense partonic medium and not alone due to Canonical Suppression effects STAR Preliminary  meson : Partonic Collectivity and Thermalization The collectivity observed in heavy-ion collisions at RHIC is due to partonic interactions. Hints of formation of some kind of thermalized (partial?) system Next meson as a probe for QCD phase boundary QGP Meet 2008 : Bedanga Mohanty

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 due to dense partonic matter formation -- Substantial v2 observed in Au+Au 200 GeV -- NCQ Scaling NA49 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 QGP Meet 2008 : Bedanga Mohanty

16 v2 expectation from AMPT
Wu Kejun Default setting, ~ 10 mb No NCQ Scaling observed Large v2 ofcould bedue to KK contributions Partonic Coalescence NCQ scaling observed QGP Meet 2008 : Bedanga Mohanty

17  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 partonic medium and not alone due to Canonical Suppression effects  meson : Partonic Collectivity, Recombination and Thermalization The collectivity observed in heavy-ion collisions at RHIC is due partonic interactions. 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 of v2 -- clear indication matter went through partonic phase QGP Meet 2008 : Bedanga Mohanty

18 QGP Meet 2008 : Bedanga Mohanty
 mesons : Summary Measurements Conclusions Yield as a function of collision centrality and Beam Energy Strangeness Enhancement at top RHIC energy due to dense partonic medium formed in the collisions.  enhancement at RHIC lying between K-(bar) and  ? Azimuthal Anisotropy Measurements 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 Production :/K ratio as a function of beam energy, Width of rapidity distribution, Slope of pT spectra not from KK Coalescence at RHIC energies <pT>, Spectra compared to hydrodynamical calculations, results from photo production Early freeze out at RHIC, close to transition temperature Hadronic phase : No NCQ scaling and small v2 Partonic phase : NCQ scaling and large v2 AA collisions : Quark vs. Gluon energy loss arXiv: dAu collisions : Cronin Effect arXiv:hep-ex/ QGP Meet 2008 : Bedanga Mohanty

19 QGP Meet 2008 : Bedanga Mohanty
Highlights STAR Preliminary Strangeness enhancement at RHIC Due to formation of dense partonic medium Collectivity at RHIC Developed due to partonic interactions QCD phase boundary Small v2 and absence of NCQ scaling - Hadronic phase Large  v2 and NCQ scaling - Partonic phase QGP Meet 2008 : Bedanga Mohanty

20 QGP Meet 2008 : Bedanga Mohanty
Normal Human Heart Beats in rhythm  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 a De Divina Proportione =  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 QGP Meet 2008 : Bedanga Mohanty

21 QGP Meet 2008 : Bedanga Mohanty
Back up QGP Meet 2008 : Bedanga Mohanty

22 Hadronic matter Small v2 - Support from Models
J.Phys.G32: ,2006 URQMD partonic Supporting arguments for small  v2 for hadronic matter -- v2 large only if there is partonic interactions Largev2 from KK coalescence, but  production unlikely from KK coalescence Hence small v2 expected if matter went through hadronic phase only QGP Meet 2008 : Bedanga Mohanty

23 High pT  probing partonic matter
STAR : Phys. Rev. Lett. 99 (2007) STAR Preliminary STAR : arXiv: 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 Understand difference in quark vs. gluon energy loss arXiv: QGP Meet 2008 : Bedanga Mohanty

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