[Clas12_deepana] CLAS12 Deep Process Analysis Meeting

[Harut Avakian]

Dear All,

Following Stepan's request, as a follow up on our discussion about the 
"weird pi0 peak" in the invariant mass distribution

of e+ and e- I produced the difference of azimuthal angles of positron 
with the DIS e- and 2nd e-, supposedly going to the calculation of the 
invariant mass. You can find that plot in 
https://userweb.jlab.org/~avakian/tmp/fake-pi0-in-eplus-eminus.pdf

The difference between positron and the DIS electron is ~180 degrees.

Slide-2 shows the angle between e+and e- (DIS electron is noted as 
e-DIS)  for the events in the "pi0 peak"

Few more slides were produced to understand better the fake peak using 
the RGA-SIDIS MC sets.

Slide 3  shows generated and reconstructed spectra of e+e- (e'-DIS 
always in the event) and possible appearance of the "pi0 peak" in the MC.

The statistics is not great, but as one can see from slide-4 the 
azimuthal angle differences are consistent with what we see in the data.

Note: the peak is shifted to lower energy compared to data, but is 
clearly separated.

Slide-5 shows that the "fake pi0 peak" is most likely coming from pi0s 
with a shift of peak observed in experiment, due to energy values for 
reconstructed electrons (dashed lines ~ 1GeV), coming higher than their 
generated values (solid lines).  Will be great to find out how exactly 
that happens, if that is indeed the case.


Regards,

Harut