[G12] g12: EC corrections for photons

[Michael C. Kunkel]

Greetings Andrea,

I am cc'ing g12 this message as it pertains to g12 data analysis.

Back in 2010, g12 investigated the photons detected in the EC. Diane 
Schott and I independently worked out a set of corrections for the MC 
that was with .1% of each other. However, these corrections never made 
it into the g12 analysis procedures because at the time, no one was 
using EC photons. At the time, the kinematic fitter was not yet mature 
enough nor understood on the g12 dataset, so we hadn't used it for this 
study.
Later, after the fitter was understood, g12 wanted to perform the EC 
photon corrections, but never got around to it.
Keep in mind that the Kinematic fitter and EC photons assumes the 
photons come from the center of the target which is located at the 
center of CLAS. In g12 this is not that case at the target as not at 
CLAS center, so if you pursue this avenue, you should consider this aspect.

However, for the rudimentary corrections Diane and I derived, I remember 
the procedure and it was simply plotting the ratio of the reconstructed 
photon energy with the generated energy (for that event), vs the 
generated energy. You should see an exponential decay, very much like 
the tail of a Poisson Distribution.

The data correction was different, it was derived from gamma p -> p pi0 
where pi0->e+e-gamma.
Here, I cut the MxP -> pi0 and by using several 4-vector conservations, 
I was able to get a correction factor for gamma to create e+e-gamma = pi0.
I can try to hunt the results and study, but I think it's easier to just 
reproduce them if you wanted to.

Whichever you decide, I can help in either way.
I know most of this information is somewhere on the g12 wiki, either on 
my page, which also links to the g7 page, or maybe Dianes page has it.

BR
MK
----------------------------------------
Michael C. Kunkel, PhD
Forschungszentrum Jülich
Nuclear Physics Institute and Juelich Center for Hadron Physics
Experimental Hadron Structure (IKP-1)
www.fz-juelich.de/ikp

On 11/20/18 12:02 PM, Andrea Celentano wrote:
> Dear Michael,
> I write you to ask if in g12 anyone has already looked at the 
> corrections to apply to photons measured in EC.
>
> I see that, for g11, a robust procedure has been set up by Dustin 
> (see: 
> https://misportal.jlab.org/ul/Physics/Hall-B/clas/viewFile.cfm/2011-004.pdf?documentId=632). 
> This procedure is based on kinematic fit of the gamma p -> p pi+ pi- 
> gamma reaction, correlating the measured gamma 4-momentum with the one 
> obtained to the kinfit of p pi+ pi- with missing gamma hypothesis.
>
> I'd like to repeat the same exercise for g12, benefiting from the 
> kinematic fit code you sent around as part of your efficiency studies. 
> However, before doing so, I'd like to check that this has not yet been 
> done. I'd like to join next g12 meeting (next week) to discuss this, 
> but to gain some time I write you in advance to know this.
>
> Thanks,
>
> Bests,
> Andrea
>