[d2n-analysis-talk] Spike at E/p=0 [SOLVED, but begs a new question]

[Brad Sawatzky]

On Wed, 15 Dec 2010, David Flay wrote:

> On Wed, Dec 15, 2010 at 4:29 PM, Brad Sawatzky <brads at jlab.org> wrote:
[ . . . ]
> > Please verify that the raw ADC information is zero for these bad
> > events.  By raw, I mean the non-corrected data containing the raw
> > bin value returned by the 1881 hardware.
> 
> Attached you'll find an *.eps file containing plots of a typical ADC
> spectrum (block index #7 of PRL1 and PRL2)  with various cuts
> (explained in the title of the graph).  We can see that the majority
> of events that had a bad momentum (p = kBig) are accounted for here
> (when E/p ~ 0).

I'm not sure I follow...

There are three ways E/p == 0:
  1) the code assigns E/p = 0 as a default value,
  2) the code assigns E/p = 0 as an error/bailout,
  3) the quantity E really is 0, and/or
  4) the quantity p is huge (ie. kBig).


We need to know which of these cases is contributing to the non-physical
E/p==0 number, and whether or not that makes sense.  If some are due to
trigger or hardware problems, then we need to make sure our efficiency
corrections treat it properly.

The single adc histograms for a single PMT aren't really sufficient
since the majority of the zeros there just mean that that particular
cell didn't interact with the particle (which is quite reasonable).
What I would like to see verified is that the raw sum of the energy in
the pion rejector layers equals the (summed) pedestal value.  That is,
I want to verify that getting E=0 out of the "high-level" code really
means that we had negligible energy deposited in the cells at the lowest
level.  That would be case '3' in the list.  If that's what is
happening, then it is strange:

> > For example, at first glance, that looks like quite a few hits that
> > have generated a trigger (ie. good hit in two scintillator planes),
> > have a good track (correct? if not, p should be undefined), and yet
> > don't deposit anything in either lead-glass layer.  That's kind of
> > strange...

Some of your plots (from the first set) seem to indicate that the E/p==0
condition happens for something like 10% of the production (ie. non-
EDTM, non-pulser triggers).  That's a big number...  Is that a correct
evaluation?

If I'm wrong and it's really a 0.1% effect that is somehow amplified in
the plots shown, then we don't have to worry about it (as much, anyway).

-- Brad

-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
Ph: 757-269-5947  -<>-  Fax: 757-269-5235  -<>- Pager: brads-page at jlab.org
The most exciting phrase to hear in science, the one that heralds new
  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov