Proton absorption
-----------------------
0. A list
of elastic ocincidence runs. The first four settings have empty target
runs.
1. Look at runs 47354-6 . Central SOS momentum is 1.74
GeV/c and central angle is 50 degrees. Central HMS
momentum is 4.3343 GeV/c and central angle is 18
degrees. The beam energy is 5247 GeV. Ntuples are in this directory. The prescale factor for the singles is one.
2. The
cuts were scer_npe>.2 , -15<ssdelta<20. and
ssshtrk>1.2 ( In this case ssshtrk is the total energy,
NOT energy/momentum. In the coin ntuple ssshtrk is E/p ). At first I
did not have the empty target run, a plot
shows W with the above cuts
(solid line) and W ( dashed line) with an additional cut of abs(ssytar)
< 1 to try and reduce target wall contribution.
3. Kinematic matching at this setting is almost perfect in the
horizontal angle. A SOS yptar of -0.06 radians relative to
central SOS angle matches to an HMS yptar of +0.025 radians relative to
central HMS angle. For the vertical angle the
mismatch is the ratio of momentum so HMS is smaller by a factor
of 1.74/4.33 . This is shown in a
plot of HMS xptar ( vertical axis) versus yptar ( horizontal axis)
with a cut on SOS ( scer_npe>.2 , -15<ssdelta<20. ,
ssshtrk>1.2 and abs(ssytar)<1 ) plus a cut of 0.9 < W < 1.0
GeV.
4. To the above cuts I added a cut of abs(ssyptar)<.05 to
insure that the SOS singles elastic ep event should have hit the HMS.
First plots of W and plots of SOS xptar ( vertical
axis) versus yptar with these cuts for the two event types. One
can see that there are not many elastic ep SOS singles events ( bottom
W plot). Plots of W with
these cut on W of 0.9 to 1.0 show the total number of
coincidence is 1463 and the total number of singles is 71 so the
total = 1463+ 71=1676 and the ratio = 4.2% .
5. I replayed the empty
target run (47357) and I looked at the runs using a kumac.
To get the charge and correction factor the LH2 and the empty target
run I run the script get_summary.tcl in
the kumac. This needs to get scaler files from the work directory. The
empty target run is the thick dummy target which is 7.31 thicker than
the walls of the LH2 target.
6. With no cut on ssytar but having cuts of scer_npe>.2 ,
-15<ssdelta<20. , ssshtrk>1.2 and abs(ssyptar)<.05, I
subtracted the dummy run from LH2 runs. Plot
of W for LH2 and dummy targets with the y-axis being corrected yield =
count*nf with nf = correction factor/charge with the dummy
divided by an additional 7.31 . For coincidence LH2 nf = 0.0041 and for
dummy nf=0.0050 and for singles LH2 nf = 0.0037 and for dummy nf=
0.0046 . Plots of W with cut of
0.9 to 1.0 show number of coincidence = 2009 and number of single = 205
for the LH2 ( top two histograms) and for the dummy number of
coincidence = 9 and number of single = 93 . So the total number
of ep elastic coincidences is 2009-9*.005/.0041 = 1998.0 and the number
os ep elastic singles is 205-93*.0046/.0037 = 89 . So percentage loss
in the coincidence is the ratio 89/(1998+89) = 4.3% . This is
close to the number with the cut on SOS ytar of < +- 1cm. When I
apply a cut of SOS ytar < +-1cm to the dummy target data no
events pass the cut.