[G14_run] Questions about information of the initial photon

[Dao Ho]

Dear all,

Previously  I did some quick analysis of the K0 Lambda channel for g14. It
turn out that I had a very low statistics result, so I naively assumed
something was wrong with my particle selection conditions. Now, I check to
see how much statistics I have rejected with each of my selection
conditions. So far, the most important player in my selection conditions
is the information about the initial photon (from the beam).

I choose only events with None Zero photons in the RF bucket.
I choose only events with the tagger ID (tagrid) being the same for all
charges in those events. Consequently, I reject events with zero tagrID
(found no photon matching).


To my surprise, with "good" non-helicity events (at least 1 charged track
events) about half of the time I see ZERO photon in the RF bucket. In
other words, my selection removes 50% statistics because the events are
recorded with zero photon in the RF bucket. So my question is how come
this number too high? Can we do anything about it?

My second finding is about events with zero tagrID (found no matching
photons). This condition also removes about 10% of the "good" non-helicity
events. Any comment?



Here I would like to ask about the PID when cooking. My understanding is
that we measure the TOF (flight time), the fight distance, and the
curvature of a charge track. We use these to determine the beta and the
momentum of the particle. From these quantities we can derive the mass of
the particle (the so-call TOF mass). Will there be any chance that a
particle with a TOF mass of electron (<5MeV) is really the pion?
My concern is if our measure TOF is smaller than the real TOF by some
nanoseconds, we would get a bigger beta, and a smaller mass. Is my concern
a legitimate concern?

This question is because in my selection scheme of +,+, -,- tracks. Half
of the plus tracks has the mass of the positron, and the same thing
happens with the negative tracks. Naturally, I suspect that there are
pairs of e+/- created by photon, so I look for events with both e+/-. The
number of events (4 tracks, 2+, 2-) with the electron/positron pair is
about 10%. As a result, I find out there are a lot of events with only ONE
positron/electron track.
By the way, I consider the charged particle is electron if it TOF mass is
less than 5MeV.

Please let me know if you have suggestions or comments.
Sincerely,
Dao Ho