[d2n-analysis-talk] T2,T6 time walk

Tue Mar 23 18:14:34 EDT 2010

 Hi Brad and Diana,

  I am looking at run 2060 for both the TDC T2 timing correction and for the
3He 4-pass run that has mostly one track events. The plot I have here of run
2060

  http://jlab.org/~posik/d2n/BB/tracks/4pass_tracks.png

Has no cuts. I just plotted the BB.tr.n variable. But if I put a T2 cut on
it, the one track events are still small compared to the 0-tracks.

On Tue, Mar 23, 2010 at 5:56 PM, Brad Sawatzky <brads at jlab.org> wrote:

> On Tue, 23 Mar 2010, MATTHEW R POSIK wrote:
>
> > Here is the link to the plots that I refer to for the t2 timing:
> >
> >     http://jlab.org/~posik/d2n/BB/trigger/t2_walk/t6_timing/<http://jlab.org/%7Eposik/d2n/BB/trigger/t2_walk/t6_timing/>
> >
> >  I took a look at the timing on the TDCs. Your explanation makes a lot
> >  of sense. I plotted a corrected TDC 03 to carry the T2 timing and
> >  also show the TDC with no T2 timing correction (corrected_TDC03.png
> >  and uncorrected_TDC03.png). As you can see the peak is much narrower
> >  and has more events under it. But there seems like there may still be
> >  a little bit of a shoulder to the right of the dominate peak. This
> >  may be related to the self-timing peak  that I chose. There seems to
> >  be more than one peak in the DBB.t2 trigger (t2.png), I selected 560
> >  as my self-timing peak, but I am not sure that this selection is
> >  correct.
>
> I will admit that I don't really understand the DBB.t2 histogram.  Self
> timing spikes are typically 1--2 bins wide -- ie. more like the spike at
> bin 200 than the ones out >500...
>
> The Cerenkov TDC peak does look better though, so the spikes at >550
> are clearly measuring the T6-T2 time difference at some level -- maybe
> I'm just getting spooked by the log-scale (it highlights the tails on a
> gaussian and makes peaks look wider than they should)...
>
> Hmm.  I'd like to understand where all that structure is coming from
> though.  What run are you looking at?
>
> > As for the tracking variable, I thought I had fixed this too. I
> > realized this problem when looking at some physics replays for the H2
> > elastic events.  To correct it I ended up removing some cuts from the
> > .cdef file. But the cdef file that I am using now is empty. And when
> > looking at the H2 elastic events that I replayed yesterday on my
> > current d2 set up I get more one-track than 0-track events. Where as
> > when I replay a 4-pass 3He and a 5-pass N2 run I get more 0-track
> > events. These can be seen here:
> [ . . . ]
>
> Diana, could you replay this run (Matt will tell which one) and see if
> you get the same numbers?
>
> > Any suggestions on what may be causing this? Could the mwdc be too
> > tailored to the transversity settings?
>
> I don't think it should be too bad -- the optics didn't change that much
> (as indicated by Xin and Diana's plots from some time back).  There's
> some distortion at the edges of the acceptance that we can fine tune
> out, but it wasn't horrible...
>
> Are the plots you showed for T2, T6, or all triggers?
>
> IIRC, 50% no-track events for BigBite T6 triggers might be about right.
> There are a lot of gammas that fire the shower, but don't leave tracks.
>
> T2 triggers involve the Cherenkov (and so require a charged particle).
> There should be a much lower fraction of no-track events for that
> trigger type.
>
> The time-zeros for the chambers would have changed between transversity
> and d2n though (since the trigger changed).  That is one of the
> calibration constants in the DB files.  If those are only 'close' then
> subsequent cuts in the tracking code might throw out the bulk of the
> events.  The remainder (ie. tail of the peak) would still give a good
> track and reasonable reconstructed momentum though.  It would be good if
> you and Diana double checked those coefficients.
>
> -- 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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