[Clas12_dileptons] JPsi/TCS Background at high Egamma

Pierre Chatagnon pierrec at jlab.org
Fri Oct 28 17:22:21 EDT 2022

Dear all,

As there will not be a ee meeting next week here are few slides.

Attached are the results of the study I did this week after brainstorming with Rafo and Joseph.
The hypothesis we tested is the following: the reaction ep->ep pi+ pi- is our main background in this region. The electron and the pion are wrongly identified as our lepton pair. In this case the electron has high momentum while the pion has low momentum, typically below 4 GeV. This matches with observation done by Joseph and I.

To test this hypothesis, I have filtered data (Inbending and outbending) to select events with electron, pi+ and proton and treated these event as TCS events. I then superimposed the shape of the spectra obtain with TCSGen and Grape simulations and compare with data. The result can be found in the slides.

The reason why these pions are mis-identified is still unclear to me, furthermore we need to understand why the remaining pi- is undetected (most of our TCS event have no additional negative track, as I presented at the last meeting). I will study in details the scattered angle of the missing particle to determine the latter.

Nevertheless, I believe this study show that we might finally have identified the main source of background at high Egamma.

Joseph could had some of these plots in his presentation of next week.
Let me know what you think, I’ll be glad to implement any feedbacks

Have a good week end
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