[d2n-analysis-talk] T2 timing corrections

[Brad Sawatzky]

On Fri, 26 Mar 2010, MATTHEW R POSIK wrote:

> 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.

Recall that the first hit in time is
  DBB.t2[Ndata.DB.t2 - 1] for Ndata.DB.t2 >= 1
so, you're not plotting what you intended to plot.

> 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.

Make sure you haven't made an error in your code.  Your previous plots
showed a very clear correlation between those shoulder events and T6
carrying the L1A timing.  These plots look like they are missing the
correction.  Plot the corrected and uncorrected TDC histos (log scale)
on the same plot (ie. one in red, one in blue) so the effect of the
timing correction is clearly visible.

> 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
[ . . . ]
> 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.

Weird.  That structure *has* to correlate to something -- either a
trigger type and/or some detector component(s) that make up the
trigger...

If the spike at ~560 is the self-timing peak for when T2 generates the
L1A, and later times are at smaller bins (common stop TDC), then what
the heck is causing the gap from 460--280?  That gap starts 50ns after
the the trigger and ends 150ns after the trigger -- that's not physics,
that's electronics.  Take a look at the trigger diagram on the wiki and
see if you can work out what's going on.  I'll try to look at it myself
before our next meeting, remind me then if it doesn't make sense...

-- Brad

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