[d2n-analysis-talk] T2 timing corrections

[MATTHEW R POSIK]

Hi Brad,

plots that I refer to can be found here:

http://jlab.org/~posik/d2n/BB/trigger/t2_walk/<http://jlab.org/%7Eposik/d2n/BB/trigger/t2_walk/>


  So I took a look at the T2 hits for run 2060 (t2_hits_2060.ps) this shows
the hits that the DBB.t2 trigger received. I then plotted DBB.t2 making cuts
on the hits (t2_2060.ps). In t2_2060.ps the upper left is a plot of DBB.t2
with no cuts, the upper right is DBB.t2 with Ndata.DBB.t2==1 and the bottom
plot is Ndata.DBB.t2==2.  It seems that the stuff <500 shows up in the 1st
hit data and there is none present in the second hit data.

Also listed here is cor_tdc_2060.ps, which is a plot of the retimed T2 TDCs.
Originally I thought that the plateau to the right of the main peak was due
to the TDCs being timed off the T6 trigger, but even with retiming the TDCs
off the T2 trigger, some still have this plateau to the right of the main
peak.

I also plotted the T2 trigger and made cuts on it to various BigBite
Cerenkov pmts by cutting on ADCs. For example T2_adc_cut.png, I plotted the
T2 trigger with no cuts (black) I then cut on four cerenkov ADCs being
greater than 60 channels ~2photo electrons. The cut I used was the following
:

  BB.cer.a_c[xx]>60.0, where xx is the PMT in this case 5(red), 6 (violet) ,
13 (blue) and 16 (green)

I was hoping to see the peaks at chan >500 change with each ADC cut, but
looking at it, they look pretty similar regardless of the PMT that is
selected.

On Wed, Mar 24, 2010 at 4:33 PM, Brad Sawatzky <brads at jlab.org> wrote:

> 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/<http://jlab.org/%7Eposik/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
>
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-- 
Matthew Posik
Email: posik at temple.edu
Temple University Physics Dept.
Office: BA-319
Office #:  215-204-1331
WebSites:
Temple:
http://quarks.temple.edu/
d2n:
http://hallaweb.jlab.org/experiment/E06-014/
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