Direct photons at CBM

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Direct photons at CBM. Sergey Kiselev, ITEP γ direct in Hadron String Dynamics (HSD) code γ direct in Bjorken HydroDynamics (BHD) HSD and BHD predictions for CBM energy Conclusions and next steps. I. HSD reminder : ππ  ργ , πρ  πγ. - PowerPoint PPT Presentation

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  • Direct photons at CBMSergey Kiselev, ITEP

    direct in Hadron String Dynamics (HSD) code direct in Bjorken HydroDynamics (BHD) HSD and BHD predictions for CBM energy Conclusions and next steps

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • I. HSD reminder : , Agreement with the HSD team to implement c.s. for , Kapusta et.al. (Phys.Rev.D44 (1991) 2774) :ITEP team: FORTRAN subroutines with cross sections for the HSD codeElena Bratkovskaya: implementation of the cross sections into the HSD code ~ 10at s =1 GeVDivergence cut = 1 mbNews, thanks to Elena: 1. weighted averaging of c.s. with the spectral function overcomes divergence 2. some bugs were fixed

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • HSD reminder: 0 ~ 20% of are from /0>1 region and can be hardly reconstructed as from 0 direct photons

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • HSD: in-medium effectwithout IMEwith IMEIn-medium effect (IME): dropping mass + broadeningm = m0 (1 + /0) = - 120 MeV, = - 150 MeV

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • HSD: in-medium effect WA98 dataNot enough to describe the data take into account of a1 meson without IMEwith IMEmain input: main input: (/0>1)

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • reminder: emission rates with a1 mesonC.Song, PR C47, 2861 (1993). Emission rates are increased with the inclusion of a1T=150: ~ 1 GeV, factor 3() - 5 ()

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • II. (1+1) Bjorken hydrodynamics (BHD)Proper time and rapidity yPhys.Rev., D27 (1983) 140 There is no dependence onLorenz boost variable y:Landau hydrodynamical model, viscosity and conductivity are neglected

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • Photon spectrumPhoton spectrum: convolution of the photon production rates with the spacetime evolution of the collisionFor a longitudinally expanding cylinderFor proper time and rapidity y`For an ideal hadron gasMain parameters: initial 0 , T0 and Tf (at freeze-out)Connection with the local rest frame

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • production ratesThermal rates from QGP:Perturbative QCD, the lowest order in sqq g, qg qdN/d4xd3p s ln(0.23E/sT) exp(-E/T) T2/E, ZP C53, 433bremsstrahlung dN/d4xd3p s exp(-E/T) T2/E, PL B510, 98Thermal rates from hot hadron gas (HHG):effective theory for hadron interactions , , , dN/d4xd3p ~ T2.15 exp(-E/T) / exp((1.35 ET)0.77), PL B510, 98

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • Hot hadron gas (HHG) scenarioC.Song and G.Fai, Phys.Rev., C58 (1998) 1689. parameterizations for the processes , , and , in which the a1 meson is taken into account properly One can fit WA98 direct photon data by HHG scenario onlyCan one go further to the CBM energy?

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • III. HSD and BHD for CBM energywithout IMEwith IMEat high pt (/0>1) dominates both without and with IME

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • HSD and BHD for CBM energy cont.HSD: steeper slope, main contribution from (/0 >1)HSDBHD

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • HSD and BHD for CBM energy cont.at pt > 1 GeV/c direct /0 ~ ( > ) 2% both for HSD/IME and BHD

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP

  • Conclusions and next stepsHSD: direct depends strongly on in-medium mass effectFor hadron scenario at CBM one can hope direct /0 ~ > 2% at pt ~ > 1 GeV/cnext steps:Check the in-medium effect in HSDto implement c.s. for , with the inclusion of a1 meson

    10th CBM collaboration meeting, Dresden S.Kiselev ITEP