10 - H1 - Desy

7.2 Photon energy calibration 89
using already introduced electrons from Bethe-Heitler events and photons from deeply virtual
Compton scattering events, in a similar way to [66]. For BH electrons, the transverse
LAr energy was calibrated with the help of the electron transverse momentum measured
directly in the tracker. For DVCS photons the energy can be calculated indirectly using
the double angle method:
E γ T,DA =
2E e sinθ had sinθ e
sinθ had + sinθ e − sin(θ had + θ e ) , (7.3)
where E e is the electron beam energy, θ e is the polar angle of the scattered electron and
θ had is the inclusive hadronic angle. Both methods confirm the validity of the calibration
factors used in the analysis, within statistical significance.
A similar study was performed for the calibration of photons in the MC simulation. Figure
7.4 shows the comparison between MC generated E gen
T
and reconstructed ET
rec transverse
energy additionally binned in the pseudorapidity of the photon. The mean value of
the fitted gaussian resolution function corresponds to typically two percent miscalibration.
800 -1.0 < η < -0.6
µ = -0.007
600
σ = 0.043
400
200
1000
500
-0.6 < η < -0.2
µ = -0.016
σ = 0.048
1500
1000
500
-0.2 < η < 0.2
µ = -0.020
σ = 0.049
-0.2
0
-0.1 0 0.1 0.2
rec gen gen
(E -E T
)/E
T
T
-0.2
0
-0.1 0 0.1 0.2
rec gen gen
(E -E T
)/E
T
T
-0.2
0
-0.1 0 0.1 0.2
rec gen gen
(E -E T
)/E
T
T
4000
3000
2000
1000
0.2 < η < 0.6
µ = -0.029
σ = 0.049
3000
2000
1000
0.6 < η < 1.0
µ = -0.018
σ = 0.050
3000
2000
1000
1.0 < η < 1.4
µ = 0.002
σ = 0.053
-0.2
0
-0.1 0 0.1 0.2
rec gen gen
(E -E T
)/E
2000
1500
1000
500
T
T
-0.2
0
-0.1 0 0.1 0.2
rec gen gen
(E -E T
)/E
1.4 < η < 1.8
µ = 0.006
σ = 0.056
T
T
1500 1.8 < η < 2.4
1000
500
-0.2
0
-0.1 0 0.1 0.2
rec gen gen
(E -E T
)/E
µ = -0.011
σ = 0.044
T
T
-0.2
0
-0.1 0 0.1 0.2
rec gen gen
(E -E T
)/E
T
T
-0.2
0
-0.1 0 0.1 0.2
rec gen gen
(E -E T
)/E
T
T
Figure 7.4: Transverse energy calibration studied with the help of reconstructed energy
ET
rec and generated energy E gen
T
in eight bins of pseudorapidity. Distributions are consistent
with a Gaussian function with fitted mean value µ and standard deviation σ. Both
parameters are printed in the respective subfigures.
Comparison to the data miscalibration, together with other H1 analyses (particularly
DVCS study of [119]) lead to a relative MC misrepresentation of the data electromagnetic