[d2n-analysis-talk] LHRS Scintillator Study

[David Flay]

Hi all,

I've been investigating the LHRS scintillators over the past few days to
see if I can use it as an additional detector for PID purposes.

As a first step, I've been looking at the affect PID cuts (using the GC
and PR) have on the TDCs of the S1 (or S2) plane.  In particular, I have
attached a plot of typical TDC spectrum of a paddle from the S1 plane. 
This plot corresponds to the left TDC.  (In general, we have two PMTs --
one on each side of the paddle, which is oriented transversely w.r.t. the
particles as they traverse the S1 (or S2) plane.)  This plot is from the
4-pass, p = 0.60 GeV kinematic (run 20675).

On the plot are a number of cuts.  The black line is the raw spectrum. 
The blue line is an anti-Cerenkov cut -- L.cer.asum_c==0.  We see here
that it overlaps with the black line almost perfectly (!).  The red line
is a Cerenkov cut for good electrons (L.cer.asum_c>600 -- raising the cut
position sharpens this peak, and slightly reduces the rightmost peak in
the double peak).  The green line corresponds to the GC>600&&prl_E_P>0.75
-- so we look at good electrons in the E/p distribution explicitly.  This
seems like a good thing -- at least we can pick out the electrons (to some
degree).  However, it is clear that an anti-Cerenkov cut still populates
this main peak that has been illuminated by the electron cuts.

I have examined an elastic run as well -- attached as the second plot (run
1229).  We see that the electron cut (GC>600) picks out this main peak --
there is only one peak in this TDC spectrum.

Based on this double peak structure in the first plot, I'm thinking that
maybe we could benefit from a calibration of the time offsets of the left
and right TDCs, since this has a direct effect on the resolution of S1
(and hence, wouldn't that imply that we could possibly discern electrons
from pions, based on timing information -- considering the (main) trigger
requires a coincidence between S1 & S2?)  A calibration of S2 will provide
for a more accurate beta as well.

I have calibration code from Vince -- he sent it to me last year, as the
experiment was finishing up.  I've taken a look through it today, and I've
sent him some questions regarding the procedure, and possible help in the
PID area.  We'll see what he says.

Other insightful variables I've been looking at (for the calibration) are
L.s1.nthit -- this tells us the number of paddles with a L&R TDC
coincidence.  Another is the related quantity L.s1.t_pads -- this tells us
which paddle has a L&R TDC coincidence...  I was thinking of using these
as cuts -- such that if we require S1, S2 to have a coincidence in 1
paddle -- that is effectively an 'extra' trigger cut for good electrons
(?)  Of course, this fuels my interest in a calibration of the time
offsets in S1 and S2.


Any other ideas as PID checks?

Thanks,

Dave

-------------------------------------------------
David Flay
Physics Department
Temple University
Philadelphia, PA 19122

office: Barton Hall, BA319
phone: (215) 204-1331

e-mail: flay at jlab.org
            flay at temple.edu

website: http://www.jlab.org/~flay
              http://quarks.temple.edu
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