[G12] g12: EC corrections for photons

[Michael Kunkel]

Greetings,

“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”
Not the reconstruction code.
See KinLine.C, I think, for how photons are corrected.

Also my runIndex, with run = 10, should be used with photons. It should be good for all particles, as it’s just run 56855 information except EC and CC constants, which are set to run 10.

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

> On Nov 20, 2018, at 15:30, Andrea Celentano <andrea.celentano at ge.infn.it> wrote:
> 
> HI Michael,
> thanks for your detailed email.
> 
> Can you explain me why the EC assumes the photons come from the target center at z=0? If I look at the makePART.cc file in the PID package, function GammaID(), I see:
> 
> int GammaID(bid_t * tbid, int tbid_index, part_t * part){
>   int IFail = 0;
>   vector3_t zero3 = {0.0,0.0,0.0};
>   float gamma=0;
>   float p, mag;
>   clasECHB_t *ECHB = (clasECHB_t *)getBank(&bcs_, "ECHB");
>   echb_t *echb;
>   clasEC1R_t *EC1R = getGroup(&bcs_,"EC1R",tbid->sec);
>   clasMVRT_t *MVRT = NULL;
> 
>   /*look for MVRT bank. liji*/
>   if(MVRT = (clasMVRT_t *)getBank(&bcs_, "MVRT")){
>     zero3 = MVRT->mvrt[0].vert;
>   }else{
>     /*get target center position form TGEO bank. liji*/
>     zero3.z = target_z(); 
>   }
> 
> 
> It seems that, in case an MVRT bank exists, then the “zero3” is taken from it - aka the reaction vertex. In my analysis, I take events with 3 charged particles as seen by PART (p, pip, pim), hence MVRT is defined.
> 
> Anyhow, we can discuss about this at the next g12 meeting. 
> 
> Thanks,
> Andrea
> 
>> On Nov 20, 2018, at 15:08, Michael C. Kunkel <mkunkel at jlab.org> wrote:
>> 
>> 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
>>> 
>> 
> 
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