[clas12_rgk] exclusive neutral pion selection

[Viktor Mokeev]

Dear All,


There are few differences in selection of gamma_{v}  p--> pi^0 p events by Anna and FX:


  1.  Anna is using
Cook: 5.7.4
Data: skim4_5990.root (12M events)
  2.  Anna got the photon energy from the sum ECAL+PCAL converted to the photon physical energy, while FX took them directly from EB.
  3.  Anna selected events with a scattered electron, proton, and exactly two neutral which are not necessarily photons. FX selected scattered electron, proton, and > 2 gammas from EB.


I propose after completion of the simulation discussed at the July 5 RG-K Meeting, Anna repeats the selection of  gv p--> pi^0 p events from the same data set and with exactly the same selections as FX successfully accomplished. For me, FX 2gamma inv masses looks great!


 Best Regards,

                                 Victor

________________________________
From: clas12_rgk <clas12_rgk-bounces at jlab.org> on behalf of L Smith <lcs1956 at me.com>
Sent: Friday, July 5, 2019 8:57:48 PM
To: Francois-Xavier Girod-Gard
Cc: clas12 rgk
Subject: Re: [clas12_rgk] exclusive neutral pion selection

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 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
[cid:FBA9B3C0-A552-44FA-903C-BD2905E4A91A at lan]

TOP theta_gamma=15.5  BOTTOM theta_gamma=5.5  P_gamma=5 GeV
[cid:8225E136-610C-4361-B732-6F215687EEB3 at lan]

On Jul 5, 2019, at 7:44 PM, Francois-Xavier Girod <fxgirod at jlab.org<mailto: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

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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