A. ELECTRON
To study the veto efficiency on electron, one has to select on electrons
sample from the data as clean as possible. Run 1429-32 (no radiator, end-point)
was choose to do this study. Cuts are defined in the file eseting.kumac
and as below:
(1) Standard cut $1, including tcoinc, tc, ph, th, y. This is a tight
cut
on timing and loose clean up cut on the proton data.
cut $3 566<tc<604.and.480<tcoinc<540
cut $2 -0.07<th<0.07.and.-0.03<ph<0.03.and.-0.036<y<0.05
cut $1 $2.and.$3
(2) Kinematic cut $6: Requiring the position and energy of the particle
detected on the calorimeter are fully constrained by the two-body ep
scattering kinematics.
cut $6 abs(calox(6)-xcx)<3.5.and.abs(caloy(6)-ycx-1.17)<2.97
cut $6 $6.and.abs(egx-ablokss)<232
The events are selected so that they are all within one sigma of
position and energy deviation. The position offset is also taken care
of.
See veto_e_eff.eps
for the determination of the sigmas and the offsets.
(3) central calorimeter cut $61: -4<calox(6)<4.and.-4<caloy(6)<4
(4) Wire chamber cut $81.and.$82: requiring at least one cluster on
BOTH planes of wire chamber in the pb-glass central region.
(5) Forward angle cuts $97.and.$98.and.$99: requiring the particle in
the
ep direction.
cut $97 z>0.93
cut $98 -0.01<thig-thigx<0.012
cut $99 -0.01<thog-thogx<0.01
These cut appears to be a subset of cut $6, so only $6 is used for the
following analysis.
(6) veto cut: $25, requiring at least one hit on BOTH veto planes.
Whether there is a hit on veto is determined by the veto TDC
spectrum.
VETO efficiency on electron:
# of events pass (std + kinematic + central pb-glass + WC+ veto) cut
----------------------------------------------------------------------------------------------
# of events pass (std + kinematic + central pb-glass + WC) cut
884
= ------ = 95.1%
929
The cuts in the denominator and end-point condition assure that only
electrons are selected.
B. PHOTONS
The data used for this study is run 1441-46.
The only way to assure that the sample are clean photons is to choose
pi_0 events, and then select on the energy and position. The only different
cut from the above cut definition is the kinematic cuts (call it pi_0 cut):
cut $7: abs(calox(6)-xcx+0.5)>14.5.and.abs(caloy(6)-ycx-1.01)>12.4
cut $7 $7.and.abs(epig-ablokss)<232
The events are choosen so that the position on calorimeter is 3 sigma
away from the ep events. And a new variable, epig, which is the energy
of photon decayed from pi_0, is included in the ntuple to assure that the
particles of interest are indeed having the right energy. The energy
resolution 232 MeV are taken from ep study. The plots of position and
energy deviation is shown on veto_g_eff.eps.
Note the lower-right plot. The solid line represents the events pass the
"standard cut", and the dash line represents the events pass the "standard
+ pi_0" cuts. To assure that we pick up only the photons, we further require
that z<0.8 and no WC fires in the region of interesting:
VETO efficiency on photon:
# of events pass (std + z<0.8 + pi_0 + no WC + VETO)
----------------------------------------------------------------------------
# of events pass (std + z<0.8 + pi_0 + no WC)
10
= ----- = 4%
239