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

Tue Mar 23 14:53:45 EDT 2010

Hi Brad,

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/

 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.

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:

http://jlab.org/~posik/d2n/BB/tracks/

I checked my analyzer setup. I am currently using Brad's version of the
analyzer ( the one with the THaDecData fix) so when I do "which analyzer" I
get:

/home/brads/d2n_analysis_copy/analyzer/analyzer

I am symbolicly linked to the bigbite library:

 /usr/local/d2n_analysis/d2n/bigbitelib/libBigBite.so

The only other difference that I can think of is that I am using my DB with
the cer ped corrections. But this DB was "diffed" with the current DB and
all files are the same with the exception of the altered BB.cer file.

Any suggestions on what may be causing this? Could the mwdc be too tailored
to the transversity settings?

On Tue, Mar 23, 2010 at 10:46 AM, Brad Sawatzky <brads at jlab.org> wrote:

> On Mon, 22 Mar 2010, posik at jlab.org wrote:
>
> > I also wanted to see what the un-prescaled t2 and t6 look like
> > (t2vst6.png) where T2 is the y-axis and T6 is the x-axis. I also tried
> > to plot the variable DBB.l1a , but I just get a white canvas and zero
> > entries. I was wondering is this because DBB.l1a is an un-prescaled
> > variable and the l1a triggeres only for prescaled triggers? Or is this
> > a crate map type error?  There is also a variable called DBB.f1l1a
> > which I assume is the l1a going to f1 TDC?
>
> The L1A *is* the trigger -- if you read out an event, then there was an
> L1A.  (The L1A is always after prescaling, but that doesn't matter
> here).
>
> >  I am a little confused on how to actually go about correcting for
> >  this time walk effect. Do I apply corrections to the t2 vs TDC or do
> >  I really want to correct the t2 vs t6 since t2 is our primary
> >  trigger?
>
> A hit in a TDC is the time difference between the trigger and the
> individual hit coming into the TDC.  For example:
>  dT = T_hit - Trigger
> For our "standard" events, the trigger is T2, so
>  dT = T_hit - T2
> However, we also have a class of events where we get a T2 and a T6, but
> the T6 carries the timing (due prescaling and the way the Cerenkov is
> ANDed with the T6 to form T2).  For this case you have
>  dT = T_hit - T6
> You want your histogram to always reflect the dT between the hit and T2
> so you can do this
>  dT = T_hit - T6 + (T2 - T6) + const
> where (T2 - T6) is just DBB.t2.  The 'const' is the value of the self
> timing peak in DBB.t2
>
> >  Also I am a bit concerned with ~95% of my statistics being lost with
> >  a one track cut(BB.tr.n==1). Could this be a problem with the optics
> >  or mwdc data files? Diana are you also seeing a large decrease in
> >  statistics with this cut?
>
> You had this problem before -- are you certain you're using the standard
> analyzer build?  (ie. Environment variables are all correct?)
>
> -- 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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