[d2n-analysis-talk] Fwd: LHRS Scintillator Calibration Study

[Brad Sawatzky]

On Thu, 04 Mar 2010, David Flay wrote:

> On Thu, Mar 4, 2010 at 10:16 AM, Brad Sawatzky <brads at jlab.org> wrote:
> 
> > I assume you're referring to the second band in the S1 time average at
> > 67ns.  That is usually indicates that you're histogramming two different
> >
> > trigger types: ie. T3, T4.  Double check that your trigger cut is doing
> > what you think it's doing.
> 
> Yeah -- that's the band I'm talking about... These are the cuts I use:
> 
>            //one track from the target
>            cut0 = Form("(L.tr.n==1)");
>            //trigger cuts
>           cut0 += Form("&&(DL.edtpl==0)&&((DL.
> evtypebits&(1<<3))==(1<<3))");
> 
> I've always used this trigger cut, and I haven't seen any structure that
> looked 'odd' until now... For comparison, here's a comparison of run 20263
> (p = 1.42 GeV, 5-pass) and run 20207 (p = 1.70 GeV, 5-pass)... strange.
> Notice how the band becomes more prominent at higher p.

Vince pointed out the answer.  Your cuts are working correctly -- the
second band are cosmics going through the stack 'backwards'.  Note that
for good electrons (bulk of the data) t_2m-t_s1=6ns, but for the second
band: t_2m-t_s1=-6ns.  At high p0 we have so few electrons that cosmics
actually compete.  Interesting.

-- 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