1. 28.09.2007 10th CBM collaboration meeting, Dresden S.Kiselev ITEP 1 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

2. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 2 I. HSD reminder : ππ  ργ, πρ  πγ Agreement with the HSD team to implement c.s. for πρ  πγ, ππ  ργ Kapusta et.al. (Phys.Rev.D44 (1991) 2774) : ITEP team: FORTRAN subroutines with cross sections for the HSD code Elena Bratkovskaya: implementation of the cross sections into the HSD code σ ππ ~ 10σ πρ at √s =1 GeV Divergence  σ cut = 1 mb News, thanks to Elena: 1. weighted averaging of c.s. with the ρ spectral function overcomes divergence 2. some bugs were fixed

3. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 3 HSD reminder: ω  π 0 γ ~ 20% of γ ω are from ρ/ρ 0 >1 region and can be hardly reconstructed as from ω  π 0 γ  direct photons

4. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 4 HSD: in-medium effect channel πρ  πγπ π  ργ ω(ρ/ρ 0 >1) dN γ /dy(y c.m. =0)0.37/1.050.27/0.360.14/1.20 !!! without IMEwith IME In-medium effect (IME): dropping mass + broadening m = m 0 (1 +  ρ/ρ 0 )  ω = - 120 MeV,  ρ = - 150 MeV

5. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 5 HSD: in-medium effect – WA98 data Not enough to describe the data  take into account of a 1 meson without IMEwith IME main input: πρ  πγ main input: ω(ρ/ρ0>1)

6. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 6 reminder: emission rates with a 1 meson C.Song, PR C47, 2861 (1993). Emission rates are increased with the inclusion of a 1 T=150: ~ 1 GeV, factor 3(γ πρ ) - 5 (γ ππ )

7. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 7 II. (1+1) Bjorken hydrodynamics (BHD) Proper time  and rapidity y Phys.Rev., D27 (1983) 140 There is no dependence on Lorenz boost variable y: Landau hydrodynamical model, viscosity and conductivity are neglected

8. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 8 Photon spectrum Photon spectrum: convolution of the photon production rates with the space– time evolution of the collision For a longitudinally expanding cylinder For proper time  and rapidity y ` For an ideal hadron gas Main parameters: initial  0, T 0 and T f (at freeze-out) Connection with the local rest frame 

9. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 9 γ production rates  Thermal rates from QGP: Perturbative QCD, the lowest order in  s qq  gγ, qg  qγ dN/d 4 xd 3 p   s ln(0.23E/  s T) exp(-E/T) T 2 /E, ZP C53, 433 bremsstrahlung dN/d 4 xd 3 p   s exp(-E/T) T 2 /E, PL B510, 98  Thermal rates from hot hadron gas (HHG): effective theory for hadron interactions πρ  πγ, ππ  ργ, ρ  ππγ, ω  πγ dN/d 4 xd 3 p ~ T 2.15 exp(-E/T) / exp((1.35 ET) 0.77 ), PL B510, 98

10. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 10 Hot hadron gas (HHG) scenario  C.Song and G.Fai, Phys.Rev., C58 (1998) 1689. parameterizations for the processes ππ →ργ, πρ → πγ, and ρ →ππγ, in which the a 1 meson is taken into account properly One can fit WA98 direct photon data by HHG scenario only Can one go further to the CBM energy?

11. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 11 III. HSD and BHD for CBM energy channel πρ  πγπ π  ργ ω(ρ/ρ 0 >1) dN γ /dy(y c.m. =0)0.11/0.390.10/0.210.11/0.89 !!! without IME with IME at high p t ω(ρ/ρ 0 >1) dominates both without and with IME

12. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 12 HSD and BHD for CBM energy –cont. HSD: steeper slope, main contribution from ω (ρ/ρ 0 >1) HSD BHD

13. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 13 HSD and BHD for CBM energy – cont. at p t > 1 GeV/c γ direct /γ π0 ~ ( > ) 2% both for HSD/IME and BHD dynamicsHSDBHD IME+- a 1 meson-+

14. 28.09.200710th CBM collaboration meeting, Dresden S.Kiselev ITEP 14 Conclusions and next steps  HSD: γ direct depends strongly on in-medium mass effect  For hadron scenario at CBM one can hope γ direct /γ π0 ~ > 2% at p t ~ > 1 GeV/c  next steps: Check the in-medium effect in HSD to implement c.s. for πρ  πγ, ππ  ργ with the inclusion of a 1 meson