[Frost] Vertex issues

[Michael Dugger]

Hi,

Brian M. and I have been looking at the vertex reconstruction for the 
reaction "gamma p -> p X" binned in lab-momentum and lab-angle.

It looks like we have problems with the vertex reconstruction.

The z-vertex is highly dependent upon momentum and angle for the scattered 
proton. For angles below 20 degrees we may not even be able to untangle the 
Butanol from the carbon using simple cuts on z-vertex. This would make the 
carbon subtraction for the angles < 20 degrees difficult.

Also, it appears that the vertex for Butanol is being "pulled" towards the 
forward direction for low momentum and angle.

For angles less than 20 degrees we see a lot of contamination from the 
Butanol in the Carbon target. The huge amount of contamination might 
explain why CMU is seeing Hydrogen like events in the Carbon target even 
with a 10% confidence level cut. It might be good to see how many events 
from the Carbon target survive the 10% confidence level cut as a function 
of momentum and angle.

We have plots of the z-vertex for the recoil proton from the reaction 
"gamma p -> p X". In what follows, momentum is in units of MeV/c and theta 
has units degree. (Brian is producing similar plots for pi+ and pi-)

First a "nice" plot where
1625 < p < 1650 and 30 < theta < 40
http://www.jlab.org/~dugger/g9/g9a/tmp/T35-p1625.gif

The line is a fit using

Background-> constant term

Butanol -> Convolution of flat distribution from -2.6 to +2.6 with 
a Gaussian

Carbon -> Gaussian centered at the physical target location

CH2 -> Gaussian centered at the physical target location

NOTE: Only the amplitudes and a single width of all the gaussians are 
allowed to vary.

The above distribution fits the function well.

Now the ugly stuff:

375 < p < 400 and 10 < theta < 20
http://www.jlab.org/~dugger/g9/g9a/tmp/T15-p375.gif

375 < p < 400 and 20 < theta < 30
http://www.jlab.org/~dugger/g9/g9a/tmp/T25-p375.gif

375 < p < 400 and 30 < theta < 40
http://www.jlab.org/~dugger/g9/g9a/tmp/T35-p375.gif

600 < p < 625 and 10 < theta < 20
http://www.jlab.org/~dugger/g9/g9a/tmp/T15-p600.gif

600 < p < 625 and 20 < theta < 30
http://www.jlab.org/~dugger/g9/g9a/tmp/T25-p600.gif

600 < p < 625 and 30 < theta < 40
http://www.jlab.org/~dugger/g9/g9a/tmp/T35-p600.gif

775 < p < 800 and 10 < theta < 20
http://www.jlab.org/~dugger/g9/g9a/tmp/T15-p775.gif

775 < p < 800 and 20 < theta < 30
http://www.jlab.org/~dugger/g9/g9a/tmp/T25-p775.gif

775 < p < 800 and 30 < theta < 40
http://www.jlab.org/~dugger/g9/g9a/tmp/T35-p775.gif

The question that we must ask: Does the tracking need to be calibrated 
again?

-Michael