[d2n-analysis-talk] Trigger Plots for Coin. and LHRS runs (& evtypebits description)

[Brad Sawatzky]

On Mon, 26 Oct 2009, David Flay wrote:

[ . . . ]

> I'm thinking that the hierarchy is L1A->TDC histograms & ADCs.  If
> that's the case, wouldn't I see 8 peaks in the L1A (one for each
> trigger)? So that, I could cut on evtypebits and pick out each of the
> peaks, corresponding to each trigger? I've tried this, but some
> triggers pick out one peak, and others pick out a few, and they tend
> to overlap.

You have this
  T1 ---\
  T2 --- \                                  ___(*)__ TDC ComStop
  .       >-- TrigSup[prescaling] --> L1A -<
  .      /                                  \__(*)__ ADC Gates
  T8 ---/

The L1A generates the common stop for the TDC channels.  Each of the
channels on the TDC only (DL.bitX) views the pulses from a single
trigger.  Depending on what detector package forms the trigger, we
sometimes "retime" the L1A (indicated by (*) so that it carries the
timing of a detector package more appropriate for one set of ADCs/TDCs.
If this is done, it can spread the self-timing spike you would expect
into a gaussian (usually).

> However, I'm not sure I trust this variable I'm using -- it's
> 'DL.L_l1a', as opposed to 'DL.l1a' (this is a coin. run I'm looking
> at, run 1229, so the variables that I'm working with are DL.tX, and
> not DL.LTX, for instance).  The 'DL.l1a' is not working at the moment,
> I'll take a closer look at this..

DL.L_l1a plots the L1A out of the TS (which carries the same trigger
timing as the accepted trigger) vs. whatever makes the common stop on
the TDC.  The Stop can either be a straight copy of the L1A, in which
case the histogram should be a perfect self-timing spike; or the stop
could be re-timed, in which case you'll get a more interesting
distribution that represents the time difference between the detector
sub-package that generates the trigger and the sub-package that is used
in the retiming.

-- Brad

-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
  Ph: 757-269-5947 -<>- Pager: 757-584-5947 -<>- Fax: 757-269-7848
The most exciting phrase to hear in science, the one that heralds new
  discoveries, is not "Eureka!" but "That's funny..."   -- Isaac Asimov