[Clas12_verystrange] full/half field on proton dvcs experiment and meeting tomorrow

[Lei Guo]

Hi, Guys,

Franck got back to me about the impact of full field on the proton  
DVCs experiment. Any news on the N* program?

I'm at the Gordon conference this week. If I can not make the meeting  
tomorrow, please proceed without me.

Lei

>
> Lei,
>
> I looked into it with Sébastien, and for DVCS, the acceptance is  
> actually slightly better at lower torus field, the resolutions  
> worsen however. The "good" news is that even with a factor 2 worse  
> resolution in the forward (because BdL would be half), it doesn't  
> really matter since we're still dominated by the resolution on the  
> recoil proton (detected in the central detector, for which we would  
> keep max solenoidal field right ?) and the photon.
>
> Conclusion, for DVCS, it doesn't really matter if we're at full  
> field or half field for the torus. One important thing to note is  
> that the current expected resolutions in the forward is 0.5% in  
> momentum. All the studies had been done with an expected momentum  
> resolution of 1% back in the days. So in that respect, we can  
> definitely lower the field by 50% to accommodate more experiments,  
> in my opinion.
>
> However, the resolution issues in the forward might actually be more  
> critical for SIDIS (you should check with Harut) which would run in  
> the same run group. Note that they would have increased acceptance  
> to "compensate". But I think they need to study that.
>
> I put Volker in copy of this message, as he may have comments on this.
>
> Cheers,
> Franck
>
> PS: I have a few simulation plots to show that half torus field has  
> no effect on DVCS exclusivity checks, if someone wants to see.