Direct photons. Current status

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

2
g from transport codes

• Photons from existing transport codes at the CBM
  energy (central AuAu at 25 AGeV)

g origin UrQMD HSD RQMD HIJING
prompt - - - BUT -
decays BUT - BUT ? h, w 5 ? per event h, w, D, f, K 10 ? per event
meson scatterings p? ? p?, pp ? ??, BUT - - - -
No a transport code with direct photons! Need the
meson scattering source of ?
At pt gt 1.5 GeV/c main contributions ? ? po ?, p
? ? p ?
3
HSD pp ? ??, p? ? p?
Agreement with the HSD team to implement c.s. for
p? ? p?, pp ? ?? Kapusta et.al. (Phys.Rev.D44
(1991) 2774)
spp 10sp?
at vs 1 GeV
Divergence ?scut 1 mb
ITEP team FORTRAN subroutines with cross
sections for the HSD code Elena Bratkovskaya
implementation of the cross sections into the HSD
code
4
First preliminary results with HSD

• 103 AuAu b0.5fm 25AGeV

origin pp p? ?
N? 10.9 0.023 1.7
dN?/dy 3.6 0.012 0.5
A lot of ?pp but most part is soft, 90 with
ptlt0.1 GeV/c
Very small ?p? but with least slope. Need more
statistics.
5
HSD time evolution
40 of ?? are from ?/?0gt1region ? direct photons
6
HSD comparison with WA98 data

• 103 HSD2.5 PbPb (b0.5fm) events at 158 AGeV.

Too small photons!? In-medium and A1 effects
should increase the yield.
7
Emission rates with A1 meson
C.Song, PR C47, 2861 (1993). Emission rates are
increased with the inclusion of A1
T150 1 GeV, factor 3(?p?) - 5 (?pp)
8
ECAL for direct photons

• ECAL parameters energy resolution, Moliere
  radius, acceptance, occupancy.
• ECAL for direct photons (general conception)

9
ECAL resolution/Moliere radius
Energy resolution
Volume ratio (Scin. width) / (Pb width)
10
ECAL acceptance - ?
CbmRoot/Oct/2004, ECAL at 12 m, central AuAu 25
AGeV
70 of ? reach ECAL
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ECAL occupancy
Central AuAu 25 AGeV

• 35 AGeV ? 30 higher track density
• At the beam, ? 50 cm
• 3x3 cm2 ? 22 occup.
• 10 occupancy level
• 3x3 cm2 ? ? 130 cm
• 4x4 cm2 ? ? 200 cm
• 5x5 cm2 ? ? 270 cm
• 6x6 cm2 ? ? 310 cm
• 8x8 cm2 ? ? 470 cm

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ECAL for direct photons
detect direct photons at ?c.m. 900
To cover the region ?c.m. 700 - 900 ? ?lab.
90 200, ? 200-440 cm
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Two arm ECAL for direct photons
Full 4p coverage
outer ring (310440 cm) 10000 channels 6x6 cm2
inner ring (200310 cm) 10000 channels 4x4 cm2
2p coverage 10000 channels 40 of
ECAL/TSR Two/One sector structure
14
ECAL/WA98

• 2.3lt?lt3.0, 10080 channels of the size 4x4 cm2,
  s/E5.5/vE

15
WA98 p0 suppression in central PbPb
QM06/nucl-ex/0701043 p0 data for pC, pPb as
reference for PbPb
High-pT particle production is affected by the
created medium! What about compressed
baryonic matter? CBM can study with ECAL.
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ECAL/PHENIX

• 5 m from a target, ?-900lt200
• 2 sectors, lead-glass PbGl, from WA98
• 9200 channels
• Size 4 x 4 cm2
• s/E6/vE
• 6 sectors, shaslik sampling PbSc
• 15500 channels
• size 5.5 x 5.5 cm2
• s/E8.1/vE

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Elliptic flow for ?direct
QM06 V.Pantuev/PHENIX
S.Turbide et. al, PRL 96 032303 (2006)
Within statistical and systematic errors v2 is
consistent with zero. v20 or cancellation of
different contributions?
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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 AuAu data set
R N inc / NBG
See also poster 86 by Kentaro Miki
5
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?direct h azimuthal correlation
Black AuAu Red pp
QM06 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!
20
Conclusions

• First preliminary results on direct photons from
  HSD
• Too small direct photons from HSD
• Part of ?? direct photons, role of the A1
  mesons
• ECAL for direct photons
• Two/one vertical/horizontal sectors to cover
  ycm0 region
• News from QM06
• p0 suppression at SPS! ? new observable/physics
  for CBM!
• Direct photons v2 , ? h azimuthal correlations

21
Next steps

• Direct photon study with HSD sensitivity to
  scut, in-medium effects. Include the A1meson.
• Implement two arm ECAL configuration into CbmRoot
  as an option
• Feasibility studies for direct photons by
• Subtraction method (Y.Kharlov)
• Correlation method (K.Mikhailov, A.Stavinsky)
• Internal/external conversion method (S.Kiselev)