[clas12_rgk] exclusive neutral pion selection

[L Smith]

Dear FX,

It may be the invariant mass dependence on pi0 energy is more related to opening angle. For symmetric decays the two are directly related.  There is persistent evidence of a theta,phi error in cluster angle reconstruction for PCAL which you originally noticed (it goes through zero at the mid-plane and theta=25) which would cause an accumulative error as opening angle increased.

Your study of DVCS photons in ECAL in https://logbooks.jlab.org/entry/3698803 <https://logbooks.jlab.org/entry/3698803> shows tails and shoulders in the missing energy/mass distributions.  Of course there is considerable energy loss from both transverse and longitudinal leakage at small angles (bottom two plots) so a comparison with GEMC would be instructive.  

Best regards,
Cole


TWO PHOTON INVARIANT MASS ERROR vs OPENING ANGLE 


TOP theta_gamma=15.5  BOTTOM theta_gamma=5.5  P_gamma=5 GeV


> On Jul 5, 2019, at 7:44 PM, Francois-Xavier Girod <fxgirod at jlab.org> wrote:
> 
> Dear all
> 
> I posted some plots for my selection of exclusive neutral pion events from run 5700 here
> 
> https://logbooks.jlab.org/entry/3698969 <https://logbooks.jlab.org/entry/3698969>
> 
> I get only few statistics with two photons in the FTCal but I get a decent sample (10k events) with the two photons in the ECal. Checking the pi0 mass dependence I did not find a polar angle or much azimuthal angle dependence, but I do see a bit of dependence on the pi0 energy
> 
> Best regards
> FX
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