[E16-e1f] DVCS generator

[Harut Avakian]

Dear All,
Here are some clarifications on DVCS discussion we had Today.
1) Distributions of DVCS photons around \phi=0 and 360 in the data and MC:
Since P_1 (propagator of incoming electron) goes to 0 near the 
collinearity limit, the DVCS generator has a cut, which you can normally 
control through the command line
option    "--ycol " defining variable "cl_ycol" with default value of 0.005
The generator has a cut   on abs(rP1).le.cl_ycol  , means events with 
P_1<0.005 are not considered. I suggest to put a cut in the analysis 
P_1>0.01 (accounting the resolutions)
for both, data and MC.

2) Photon energy:
The calibration constant of EC deposition to photon/electron energy is 
different in MC and data (not tuned for MC). We decided to apply the 
correction offline instead of
changing the constants in the MC. The correction factor could be 
estimated taking the ratio of generated to reconstructed photon energies 
in the MC. My rough estimate
is 0.85 (means we have to divide the reconstructed MC photon energy by 
0.85 to get the correct one). That factor seem to have little dependence 
on the energy, but that can be checked in more details with high  
statistics studies of generated vs reconstructed photon momenta from 
Aram's MC.

Best,
Harut