[d2n-analysis-talk] LHRS Scintillator Calibration Study

[Brad Sawatzky]

On Wed, 03 Mar 2010, David Flay wrote:

[ . . . ]
> The same may be said of S2m. (The lower two plots). (Note, for d2n, S2 =
> S2m).
> 
> The beta_track_20675_3_2_10.pdf plots beta in the upper panel, and beta
> against the tracking x variable.
> 
> Beta is dependent on the time-of-flight between S1 and S2m, so it's
> appropriate to see how beta looks.  We see beta is ~ 0.92 in the upper
> plane.  Ideally, this should be ~1.
> 
> In the lower plane, we see that beta is approximately constant as a
> function of the tracking variable x (in the Hall coordinates this is the
> vertical axis).  I am concerned about the region x ~ 0.15-0.20 -- there's
> a bit of a blip there.

Definitely a problem here.  That should be fixed.

There is also a rather pronounced 'droop' in the plot vs. X (drops down
towards the middle and then rise back to ~1 again).  I guess that is due
to the slight upward bow in the s2m 'time average vs. paddle' plot...

> It seems like beta could use some tweaking to get it closer to 1 (?)

The glitch in beta vs. X at X=0.2 needs to be fixed for sure.  While
you're at it, you may as well tweak the t0 the offsets for the other
paddles too.  That will tighten up the peak in beta quite a bit.

Check with Transversity first to see if they have these corrections in
their DB already.

Note from these plots that any tight cut around beta=1 is _guaranteed_
to bias the data in favor of certain regions of the focal plane for
reasons that have nothing to do with physics.  This is an interesting
example of why we have to carefully check all of the low-level
calibrations before we can rely on high-level cuts to do what we expect
(beta, momentum, theta, phi, etc).

-- Brad

-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
  Ph: 757-269-5947 -<>- Pager: 757-584-5947 -<>- Fax: 757-269-7848
The most exciting phrase to hear in science, the one that heralds new
  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov