1 Jozsó Zimányi (1931 – 2006)

2 Jozsó Zimányi I met Prof. Zimányi in India in Member, NA49 and PHENIX Collaborations Nuclear Equation of State with derivative scalar coupling. ALCOR : A Dynamic model for hadronization. Particle ratios in heavy ion collisions. Charmed and strange hadron productions in heavy ion collisions. Exotic particles in heavy ion collisions. Quark and hadro-chemistry.

3 Photon and dilepton production in heavy-ion collisions Bikash Sinha Saha Institute of Nuclear Physics and Variable Energy Cyclotron Centre Budapest July 2007

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5 Contemporary Wisdom (Again?) Lattice Calculation F.Karsch’95 No Quarks:Pure SU(N) gauge theories  Phase transition Second order for N=2  1 st order for N=3

6 QCD n f light quarks  Phase transition 1 st order n f  3  seems to be continuous for n f =2 T c  number of partonic degree of freedom in units of the string tension T c /  T c (n f =2)  150 MeV T c ( n f =0)  160 MeV  Glue balls O(1GeV)

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9 QCD Phase Diagram Quark Matter

10 HOT DENSE HADRON MATTER EQ of State Chiral Properties m * x Radiative Properties of the Sizzling Hadrons MELTING PROPERTIES ? ( Decay widths ) Chiral Hadrodynamics Mesons, Vector mesons, Baryons No Universal law of m * x Brown – R HO Scaling law does not seem to hold Ie,

11 Medium effects : (Finite Temp Field th.) P. Roy, S. Sarkar, J. Alam, B.S., Nucl Physics A 653 (1999) S. Sarkar, P. Roy, J. Alam, B. S. Phys. Rev. C (1999) & Annals of Phys 2000 f v Coupling between electromagnetic current & vector meson Field, ω 0 Continuim Threshold Should not J. Alam S. Sarkar T. Hatsuda T. Nayak B. S. (2000)

12 VARIATION OF VECTOR MESON MASS WITH TEMPERATURE Sarkar et al. NPA 1998

13 Photons Hadronic matter Quark matter  qg->q   qq->g     

14 B.S. PLB 1983 R   /  +  - = const( ,  s  q q Light from QGP   qq   +  - ~ T 4

15 Dileptons Hadronic matter Quark matter  e + e - qq->  e + e -  e + e - qg -> q  *  e + e - qq -> g  *

16 Space time evolution Relativistic hydrodynamics ∂  T   Transverse expansion with boost invariance in the longitudinal direction Equation of state : Bag model for QGP and resonance gas model for hadrons

17 Isentropic expansion : Hydrodynamics takes care of the evolution of the transverse motion.

18 Alam et al. PRC (2003) Data from: Aggarwal et al. (WA98 Collaboration) PRL (2000) 3595 Direct Photons at SPS

19 J. Alam, S. Sarkar, T. Hatsuda, J. Phys. G (2004) CERES

20 Radiation at RHIC J. Alam, J. Nayak, P.Roy, A. Dutt-Mazumder, B.S.: nucl-th/ Jour. Phys. G (2007)

21 Sometime ago it was noted that: “The ratio of the production rates (  /  +  - ) and (  o,  /  +  - ) from quark gluon plasma is independent of the space time evolution of the fireball”. Universal Signal : Only a function of universal constants. (1) (2) (3) B.S. PLB 1983

22 Invariant yield of thermal photons can be written as Q  QGP M  Mixed (coexisting phase of QGP and hadrons) H  Hadronic Phase is the static rate of photon production  convoluted over the space time expansion. Thermal Photons

23 Thermal photons from QGP : using hard thermal loop approximation. Again, Resumming ladder diagrams in the effective theory Thermal photons from hadrons : (i)    (ii)    (with , , ,  and a 1, in the intermediate state) (iii)    (iv)   ,    and    & Similarly from strange meson sector Collinear equation:

24 Rather similar to photons, dileptons can be efficient probe for QGP – again not suffering from final state interactions. One has to subtract out contributions from: (a) Drell–Yan process, (b) Decays of vector mesons within the life time of the fireball (c) Hadronic decays occurring after the freeze out. Invariant transverse momentum distribution of thermal dileptons (e + e - or virtual photons,  *): integrated over the invariant mass region: Dileptons

25 Dileptons from light vector mesons ( ,  ) &  (Hadronic Sector) : Consistent with e + e - V(  ) data f V (V) : coupling between electromagnetic current and vector meson fields m V and  V are the mass and width of the vector V and w 0 are the continuum threshold above which the asymptotic freedom is restored.

26 The number density as a function of temperature. Effect of mass modification and width modification is shown.

27 Photons at SPS

28 Photons at RHIC J. Alam, J. Nayak, P.Roy, A. Dutt-Mazumder, B.S.: J. Phys. G 2007

29 Di-electrons at RHIC

30 RESULTS from the ratio: The variation of R em (the ratio of the transverse momentum spectra of photons and dileptons) has been studied for SPS, RHIC and LHC. Simultaneous measurements of this quantity will be very useful to determine the value of the initial temperature of the system. R em reaches a plateau beyond P T =1 GeV. The value of R em in the plateau region depends on T i but largely independent of T c, v o, T f and the EOS.

31 Ratio (R em ) at SPS

32 Ratio (R em ) at RHIC

33 Ratio (R em ) at LHC

34 Ratio (R em ) for pQCD processes FILTERING OUT pQCD PHOTONS

35 arXiv: [nucl.th] Ratio (R em ) vs. Initial Temperature

36 OBSERVATIONS: 1.The medium effect on R em is negligibly small 2.Hydrodynamic effects such as viscosity, flow get sort of erased out by observing the ratio, R em 3.Equivalently, model dependent uncertainties also get cancelled out through R em 4.Contributions from Quark Matter increase with the increase of the initial temperature – a)thermal photons mostly for hadronic phase at SPS b)thermal photons from RHIC and more so from LHC originate from QGP 5.R em flattens out beyond p T ~ 0.5GeV 6.R em increases with initial temperature and flattens out beyond T i ~ 800MeV 7.In the plateau region: R em LHC > R em RHIC >R em LHC 8.EOS including quasi particle in the quark matter is being tackled.

37 The ratio, R em seems to be insensitive to EOS, medium effects on hadrons, final state effects, T c, flow. However, it is sensitive to T i R em can be used to estimate T i.

38 OBSERVATIONS, contd. WHY & HOW R em (in Born approx.) => At the end R em still remains by far and large model independent: SPS => RHIC => LHC Thus R em is a universal signal of QGP, model independent and unique.

39 We see that is a function of the universal constants and the temperature. Because of the slow (logarithmic) variation as with temperature, one can assume In an expanding system, however, R em involves the superposition of results for all temperatures from T i to T f, so the effective (average) temperature, T eff will lie between T i and T f and This explains: It is also interesting to note that for  s = 0.3, T=0.4GeV, (  M) 2 ~ 1 (M max =1.05, M min =0.28), we get: R s ~ 260. This is comparable to R em obtained in the present calculation.

40 WHAT DO WE EXPECT at LHC

41 Photons and di-electrons in the ALICE experiment Photons Electron-pairs

42 Muon chambers PMD Modules PMD photons PMD photons MUON arm  -pairs MUON arm  -pairs ALICE Experiment at LHC

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44  /e + e - as well as     at the Large Hadron Collider LOOKING FORWARD TO THE VERIFICATION OF THE UNIVERSAL SIGNATURE:

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