User name R. Michaels
Log entry time 00:58:31 on June11,2004
Entry number 125303
This entry is a followup to: 125294
keyword=Trig biases make alignment difficult
Looking at the blobs in X-Y distribution (fig1), and cutting near
one (red box) or the other (green box) we get momentum spectrum
in fig 2 (the units are MeV/c). Equivalently you get the peak
near 0 in momentum if you simply require a large ADC signal in
HAPPEX detector. This is not elastic/inelastic spectrum, this is
a trigger bias effect. The stuff that makes scint triggers gets
blocked by the HAPPEX detector (it seems to block a lot more than
during our first experiment). And the stuff that make T2 is confined
to the HAPPEX detector. So you get distortions, edge effects, a
How to align ?
There are two possible ways:
1) Can put a large scint that fills the whole acceptance IN FRONT
of the HAPPEX detector (how about S0 ?).
2) Can move the elastic peak to -3%, -2%, +2%, and +3% and deduce
from S2 triggers and the shadow of HAPPEX detector where 0% is.
These data are available from optics, but probably want to do it
without sieve. It is not much different from our original plan.