[Clas12_rgb] [EXTERNAL] Re: DVCS MC check with Mauri's new gcard

[Raffaella De Vita]

Dear All,
I also ran simulations with single particles in the FT acceptance to check the effect of the new scattering chamber. In this case, I based the analysis on the “true” geant4 information to get the intrinsic resolution. Even with this, the differences between the old and new scattering chamber are marginal. In particular I don’t see differences close to 4-4.5 degrees where particles go through the rohacell pipe. The biggest effect I see is a small loss of acceptance for electrons only at the smallest angle, close to 2.5 deg, where in the current simulation they go through a plastic ring around the exit window of the chamber: since Mauri said this is already modified in the current design and will not be there, I don’t see any problem.
Best regards,
	Raffaella

> On 22 Oct 2019, at 11:21, Stepan Stepanyan <stepanya at jlab.org> wrote:
> 
> Silvia,
> 
> I put things in motion. Bob will start wit construction of the new scattering chamber. If it will be ready before that run, we will install it.
> 
> Stepan
> 
>> On Oct 22, 2019, at 7:38 AM, Stepan Stepanyan <stepanya at jlab.org> wrote:
>> 
>> Silvia,
>> 
>> One thing to compare is the fraction of ep\gamma events per detected ep (or similarly the fraction of en\gamm per detected en pair). The only effect that the new scattering chamber may have is a bit more material in front of photons going to FT. 
>> 
>> Stepan
>> 
>>> On Oct 22, 2019, at 5:08 AM, Silvia Niccolai <silvia at jlab.org> wrote:
>>> 
>>> Hello all,
>>> following our discussion of last week, I have run pDVCS and nDVCS full simulations, and compared the outputs obtained with the standard RGB gcard and with the new one that Mauri sent us, containing his new rohacell scattering chamber.
>>> I generated roughly the same number of events for the two sets of simulations. The results are in the attached figures: noshield is the standard gcard, shield is with the new rohacell piece.
>>> I am plotting rec-gen quantities. In each of the three columns are p, theta, phi, while the lines are: electron, proton, photon, and neutron.
>>> You can try to play spot the differences, but to me it all looks pretty equal.
>>> So, I'd conclude that from the DVCS point of view the new scattering chamber has no negative impact.
>>> I didn't check with interactive gemc to make sure that the new geometry was correctly implemented, but from the gemc log of my jobs it seems like it correctly imported the "e" variations for the target.
>>> From my point of view, therefore:
>>> - if this new scattering chamber reduces the DC occupancies and thus improves ttracking efficiency, as Maurizio showed last week;
>>> - if its construction and installation won't affect our schedule;
>>> - if the other experiments' spokespeople agree I'd say we can go ahead and use it.
>>> Best regards,
>>> Silvia
>>> 
>>> <res_noshield.jpg><res_shield.jpg>_______________________________________________
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>> 
> 
> 
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