Hi Pete,
nice to see that you are trying to attack the photo-channel(s), and
nice to see that you have made some progresses already.
for the moment, i personally do not have many suggestions or comments
other than encouraging you to fish for more and cleaner event samples.
with this said, i do have a couple of simple comments:
1, although it is interesting to select events with gamma energy higher
in the delta production region, i would personally be more interested
at events with gamma energy lower than or similar to 100 MeV region.
the event rates for the lower energy region is much higher.
these events having lower proton and neutron momenta can be easierly
selected using tof information. the only problem, i am not sure, is
whether you can use the BAT scintillators for the protons going
into the far backward angles. without BAT, it might be just the
down-stream
half of the target (trying to use this cut as well) is visible and hence
the blast acceptance is really very small unfortunately for the photo
channels.
one may argue to utilize the reversed blast field to get some phase-space
back for the lower energy protons in the back angles. so, the lower
energy side is important if with the forward bending low-energy protons.
2, with all the troubles on energy resolution, especially dealing with
neutron energies
calculated from neutron tofs, you should try whatever means possible
to build on the energy information, ie., the "missing energy".
this can be done mathmatically when you do have both proton and neutron
momentum or energy information. of course, as you know, the gamma
energy
can be built after the proton and neutron vectors. in doing so, you
might not get the sharp
deuteron binding energy due to poor resolutions, but certainly you
can filter many
pion events away without even using cherenkovs besides the fact that
in backangle
regions they do not exist. [coincident events do not really require
cherenkovs!
you can take my statement to anyone.]
3, of course, you can play with H(gamma, npi+). you may also do the same
for D(gamma, npi+) or D(gamma, ppi-). these may be a fall-back
position for your
thesis. however, you should try to study
the event selection differences between them and D(gamma, pn), with the
last having much bigger opening angles (160 vs 110). and this can be
used as
your advantage
in filtering all the pion events. the only thing i do not know is how
big the
blast acceptance really is for D(gamma, pn). it is going to be very
close to a
narrow gap with the existing geometry even with a reversed field.
with this, one may argue that there is some merit to have neutron
bars in a
90deg angle region of blast. well, the world is not enough, but
tomorrow never die.
good luck. and let me know how everything goes.
Zilu
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