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Direct photons. Current status

Direct photons. Current status. Sergey Kiselev, ITEP First direct photons from HSD code ECAL for direct photons (general conception) News from Quark Matter 2006 Conclusions Next steps. g from transport codes.

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Direct photons. Current status

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  1. Direct photons. Current status Sergey Kiselev, ITEP First direct photons from HSD code ECAL for direct photons (general conception) News from Quark Matter 2006 Conclusions Next steps 9th CBM collaboration meeting S.Kiselev ITEP

  2. g from transport codes • Photons from existing transport codes at the CBM energy (central Au+Au at 25 AGeV): No a transport code with direct photons! Need the meson scattering source of γ At pt > 1.5 GeV/c main contributions:ω πoγ, πρ  πγ 9th CBM collaboration meeting S.Kiselev ITEP

  3. HSD: ππ ργ, πρ πγ Agreement with the HSD teamto implement c.s. for πρ πγ, ππ ργ Kapusta et.al. (Phys.Rev.D44 (1991) 2774) : σππ ~ 10σπρ at √s =1 GeV Divergence σcut = 1 mb ITEP team: FORTRAN subroutines with cross sections for the HSD code Elena Bratkovskaya: implementation of the cross sections into the HSD code 9th CBM collaboration meeting S.Kiselev ITEP

  4. First preliminary results with HSD • 103 Au+Au b=0.5fm 25AGeV A lot of γππ but most part is soft, ~ 90% with pt<0.1 GeV/c Very small γπρ but with least slope. Need more statistics. 9th CBM collaboration meeting S.Kiselev ITEP

  5. HSD: time evolution ~ 40% of γωare from ρ/ρ0>1region  direct photons 9th CBM collaboration meeting S.Kiselev ITEP

  6. 103 HSD2.5 Pb+Pb (b=0.5fm) events at 158 AGeV. HSD: comparison with WA98 data Too small photons!? In-medium and A1 effects should increase the yield. 9th CBM collaboration meeting S.Kiselev ITEP

  7. Emission rates with A1 meson C.Song, PR C47, 2861 (1993). Emission rates are increased with the inclusion of A1 T=150: ~ 1 GeV, factor 3(γπρ) - 5 (γππ) 9th CBM collaboration meeting S.Kiselev ITEP

  8. ECAL for direct photons • ECAL parameters: energy resolution, Moliere radius, acceptance, occupancy. • ECAL for direct photons (general conception) 9th CBM collaboration meeting S.Kiselev ITEP

  9. ECAL: resolution/Moliere radius Energy resolution Volume ratio = (Scin. width) / (Pb width) 9th CBM collaboration meeting S.Kiselev ITEP

  10. ECAL acceptance -  CbmRoot/Oct/2004, ECAL at 12 m, central Au+Au 25 AGeV ~ 70 % of γ reach ECAL 9th CBM collaboration meeting S.Kiselev ITEP

  11. ECAL occupancy Central Au+Au 25 AGeV • 35 AGeV  ~30% higher track density • At the beam, ρ ~ 50 cm: • 3x3 cm2  22 % occup. • 10% occupancy level: • 3x3 cm2  ρ ~ 130 cm • 4x4 cm2  ρ ~ 200 cm • 5x5 cm2  ρ ~ 270 cm • 6x6 cm2  ρ ~ 310 cm • 8x8 cm2  ρ ~ 470 cm 9th CBM collaboration meeting S.Kiselev ITEP

  12. ECAL for direct photons detect direct photons at c.m. ~ 900 To cover the region c.m. ~ 700 - 900 lab. ~ 90 – 200, ρ = 200-440 cm 9th CBM collaboration meeting S.Kiselev ITEP

  13. Two arm ECAL for direct photons Full 4π coverage: inner ring (200–310 cm) ~ 10000 channels 4x4 cm2 outer ring (310–440 cm) ~ 10000 channels 6x6 cm2 2π coverage: ~10000 channels ~40% of ECAL/TSR Two/One sector structure 9th CBM collaboration meeting S.Kiselev ITEP

  14. ECAL/WA98 2.3<<3.0, 10080 channels of the size 4x4 cm2, σ/E=5.5%/√E 9th CBM collaboration meeting S.Kiselev ITEP

  15. WA98: π0 suppression in central Pb+Pb QM’06/nucl-ex/0701043: π0 data for p+C, p+Pb as reference for Pb+Pb High-pT particle production is affected by the created medium! What about compressed baryonic matter? CBM can study with ECAL. 9th CBM collaboration meeting S.Kiselev ITEP

  16. ECAL/PHENIX • 5 m from a target, |-900|<200 • 2 sectors, lead-glass PbGl, from WA98 • ~ 9200 channels • Size 4 x 4 cm2 • σ/E=6%/√E • 6 sectors, shaslik sampling PbSc • ~ 15500 channels • size ~ 5.5 x 5.5 cm2 • σ/E=8.1%/√E 9th CBM collaboration meeting S.Kiselev ITEP

  17. Elliptic flowfor γdirect QM’06 V.Pantuev/PHENIX S.Turbide et. al, PRL 96 032303 (2006) Within statistical and systematic errors v2 is consistent with zero. v2=0 or cancellation of different contributions? 9th CBM collaboration meeting S.Kiselev ITEP

  18. How does PHENIX measure direct photons and v2? Measure inclusive photon yield, Ninc Measure hadron contribution components p0 and h By Monte Carlo calculate p0 and h decay background in inclusive sample, Nbg Calculate direct photon excess over hadron decays, R Measure inclusive and hadron v2 by reaction plane method Calculate direct photon v2 as R * v2inc – v2BG v2dir = R – 1 Use large statistics Run 4 Au+Au data set R = N inc / NBG See also poster 86 by Kentaro Miki 9th CBM collaboration meeting S.Kiselev ITEP 5

  19. γdirect – h azimuthal correlation Black: Au+Au Red: p+p QM’06 J.Jin/PHENIX 1/NtrigdN/dDf 1/NtrigdN/dDf Df(rad) Df(rad) Near side yield ~ 0  small fragmentation photon yield Hint of away side modification (suppressed) in AuAu! 9th CBM collaboration meeting S.Kiselev ITEP

  20. Conclusions • First preliminary results on direct photons from HSD • Too small direct photons from HSD • Part of γω – direct photons, role of the A1 mesons • ECAL for direct photons • Two/one vertical/horizontal sectors to cover ycm=0 region • News from QM’06 • π0 suppression at SPS!  new observable/physics for CBM! • Direct photons: v2 , γ – h azimuthal correlations 9th CBM collaboration meeting S.Kiselev ITEP

  21. Next steps • Direct photon study with HSD: sensitivity to σcut, in-medium effects. Include the A1meson. • Implement two arm ECAL configuration into CbmRoot as an option • Feasibility studies for direct photonsby • Subtraction method (Y.Kharlov) • Correlation method (K.Mikhailov, A.Stavinsky) • Internal/external conversion method (S.Kiselev) 9th CBM collaboration meeting S.Kiselev ITEP

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