Let me toss out a general question. It is really aimed at Doug, Chris,
and Chi, but anyone can put in their 2-cents worth.
At UNH, we have been discussing Adrian's ep elastic analysis vis-a-vis
this ongoing question of momentum resolution. It suddenly dawned on me
that we are not measuring the "intrinsic" momentum resolution (probably
everybody else already saw this) but rather some convolution of that
with angular resolution.
What is used by Adrian as well as Chris and Chi (as far as I understand)
is a comparison of the measured momentum with that expected from a
kinematics calculation based on the beam energy and measured track
angle. Thus the calculated value has a spread due to the uncertainty
in angle, and the sigma from the Gaussian fit to the difference between
the measured and calculated momenta then clearly is a convolution of
the intrinsic sigma for momentum and the sigma for angular resolution.
I note that Adrian is getting about 41 MeV, and I think Chi (or was
it Chris?) was saying 38 MeV. Those are close enough that the small
difference is probably due to differences in cuts.
So my question is: is the factor of 3 in "effective" momentum resolution
due to uncertainty in angular resolution? Or at least part of it?
Coupled to this is very poor vertex reconstruction. True ep elastic
events appear to come from vertices with a spread of several centimeters.
Given the distance to the chambers (of order a meter or so), the angular
definition is quite poor, leading me to wonder whether the bulk of the
apparent momentum resolution is actually an angular resolution problem.
Perhaps someone can enlighten me.
p.s. I apologize in advance for missing the next 2 Wednesday group
and analysis meetings (I will be in CA for my daughter's graduation
and visits with other family).
John
-- John R. Calarco Dept. of Physics Univ. of New Hampshire Durham, NH 03824 phone: (603)862-2088 FAX: (603)862-2998 email: calarco@unh.edu
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