[d2n-analysis-talk] T2 timing corrections

[Brad Sawatzky]

On Wed, 24 Mar 2010, posik at jlab.org wrote:

>   So I have been looking at this T2 timing corrections. All plots are from
> run 2060 and can be found here:
> 
> http://jlab.org/~posik/d2n/BB/trigger/t2_walk/t6_timing/trig_evo/
> 
>  The first plot 2060_t2.png shows the T2 structure on linear scale. Since
> there are more than one peak in this structure I decided to use different
> peaks as the T2 self timing peak and see how that affects the retiming.
[ . . . ]
> It seems that the T2 retiming improves the Cerenkov TDCs no matter what
> self timing peak I select. This can be seen in the 2nd and 3rd plots. I am

This should be no surprise, since the choice of retiming peak is simply
a constant offset applied to the x-axis -- it just slides all the data
left or right.

> not sure how to go about and begin to determine which of the peaks I
> should use. Any suggestions on where I may start to look?

>From the perspective of the Cherenkov TDC data, it doesn't really
matter.  In the end you'll be cutting around the peak.  It doesn't
matter where the peak is.  (I would be inclined to center it about zero
for all PMTs.)

>From the perspective of the experiment, the _real_ question is "what
does the structure in DBB.t2" mean?  The two narrow peaks out around 550
are probably due to slight timing differences in the cabling of the
different Cerenkov electronics (so you get a slightly different peak
depending on which PMT fired).  That would be easy to establish by
putting a cut on a single PMT (via track position or cherenkov ADC).

The stuff <550 is a bit of a mystery to me.  I know we talked about it
during the run -- there might be some explanation in the Halog.  It
could be multiple hits in the DBB.t2 TDC channel -- try cutting on
Ndata.DBB.t2==1 and see if you enhance the self-timing peaks.

> In the evtypebit cuts on the last plot, when I cut on
> (DBB.evtypebits&1<<7)==(1<<7) I end up with no events. I am guessing that
> this is do to the large prescale, which was at 65535?

I think that prescale (2^16-1) results in the associated trigger being
disabled at the trigger supervisor.

-- Brad

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