[E12-15-001] ep elastic data

[Mark Jones]

I looked at the elastic kinematics with SIMC.
In SHMS singles the ep phase space is determined by the electron scattering angle
and in HMS coincidence  the ep phase space is determined by the HMS in and
out of plane angles.  THerefore the range in SHMS delta is limited to
range of 6% for singles and about 3% for coincidence.

I propose to save time that we just set the SHMS central momentum to 4.184
for all elastic settings. Otherwise we would have to cycle the SHMS for each
change in ep setting.

Also the question came up about whether to run the HMS with the collimator in
since the proton can punch through. The HMS sieve is about 6.3cm thick so
the protons lose about 130 MeV which is a large compared to 800-1000MeV
protons. I added to my SIMC the possibility to punch-through the collimator
and saw very small amount of punch-through.


The ep elastic rates are high. I get the following for 20uA:
The BCM calibration linearity below 10uA is questionable.
So I would not go below 10uA and just prescale the singles or
elastic data away.

SHMS angle    HMS momentum    Single rate    Coin rate
12                          1000                       40,547/sec       5,672/sec
10.9                        900                        77,121/sec    9,209/sec
9.6                          800                      173,634/sec    17,275/sec

Please double check my rates.

Cheers,
             Mark
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