[d2n-analysis-talk] LHRS Trigger Efficiency Study

[Brad Sawatzky]

Here are the trigger definitions that should have been present for d2n:

  T3 =  S1 .and. S2
  T4 = [(S1 .and. Cer) .or. (S2 .and. Cer)] .and. (.not. T3)

So, you should never have a T3 and a T4 at the same time.
  NOTE: Please confirm that this was, in fact, the trigger setup
        for the LHRS T4 in d2n/transversity.

T8 (and any other triggers) should be actively excluded from the
following analysis (ie. cut them out).  You should also cut out EDTM
events.  EDTM triggers should always show up as a T3 since the EDTM
system injects signals into the lines running from the S1 and S2 PMTs.
This generates the conditions for a 'fake' T3.  The advantage is that we
know the T3 must show up -- if we don't see it, then it was lost due to
hardware deadtime.

The idea is that T4 should catch the good triggers that T3 misses, thus
measuring the inefficiency of T3.  So, what you do is this:
  - Get a sample of good electrons by applying cuts similar to when you
    did the cerenkov efficiency analysis (but allow the trigger type to
    be T3 .or. T4.
For the case where we have a prescale of 1 for T3, then each T4 (after
'good electron' cuts) means that we have something that looks like an
electron, but it only fired one paddle plane when both should have
fired.  So, this expression:

eff_3 = bit3/(bit3 + bit4)

  bitN = trigger N latch bit, after prescaling.  This is set 
          if and only if:
          - a TN trigger is seen at the TS within 10ns of whatever
            generated the L1A, .AND.
          - it passes the prescale condition for trigger N

will give you the effieciency of the T3 trigger.  That is, it will
answer the question: for good electrons, what fraction of the time will
T3 fire?  As defined above, it should be independent of other triggers,
prescaling, etc.

-- Brad

On Fri, 09 Jul 2010, David Flay wrote:

> I've been working with the trigger efficiencies, and I have two methods
> (see my latest talk for a description:
> http://www.jlab.org/~flay/analysis/2010/LHRS_7_1_10.pdf):
> 
> First, we can consider the ratio:
> 
> for trigger 3:
> eff_3 = bit3/(LT3+LT4)
> 
> for trigger 4:
> eff_4 = bit4/(LT3+LT4)
> 
> However, shouldn't we also include trigger 8 here:
> 
> for trigger 3:
> eff_3 = bit3/(LT3+LT4+LT8)
> 
> for trigger 4:
> eff_4 = bit4/(LT3+LT4+LT8)


> The results for this method are below:
> 
> ========== Trigger Efficiencies (Method 1) ==========
> Trigger 3: 97.1425%
> Trigger 4: 0.0700378%
> Trigger 8: 0%
> 
> (trigger 8 efficiency is zero since bit8 is prescaled at 100 for run
> 20676, and the bit8 variable yields 10 events.)
> 
> This method poses the question:
> 
> "Of all the triggers generated (setting the latch pattern) -- how many of
> the good triggers pass through the prescale condition?"
> 
> We see with this method (method 1) that the efficiencies do not add to
> 100%.  I find this to be unsettling.  Then, I considered another way of
> calculating the efficiencies:
> 
> for trigger 3:
> eff_3 = bit3/(bit3+bit4+bit8)
> 
> for trigger 4:
> eff_4 = bit4/(bit3+bit4+bit8)
> 
> The results for this (method 2) are below:
> 
> ========== Trigger Efficiencies (Method 2) ==========
> Trigger 3: 99.928%
> Trigger 4: 0.0720461%
> Trigger 8: 0%
> 
> We see here that the efficiencies <do> add to 100%, and subsequently, the
> efficiency of T4 truly evaluates the inefficiency of the T3 trigger.
> 
> This method poses the question:
> 
> "For each trigger that passes the prescale condition, we set the bit
> pattern.  Now, what percentage of those events are the good ones -- the
> T3's?"
> 
> Clearly, these two methods examine two different ways of looking at the
> inefficiency of the T3 trigger -- at the prescale (method 1) and after
> (method 2).  Both points are of concern -- since we do not want to lose T3
> triggers -- that was the point of having the prescale = 1 (method 1
> examines the loss of T3's at the prescale => trigger supervisor).  Of
> course, we should also be concerned with how many T3's are in the bit
> pattern, compared to the whole -- especially when the prescale condition
> on T8 is set to 100, and T3,T4 prescales are 1.  The fact that T3 is not a
> perfect 100% in the latter case indicates an inefficiency.
> 
> I do have concern that method 1 yields efficiencies which do <not> add to
> 100%.  This is why I considered method 2.
> 
> However, would it be more accurate to consider some linear combination of
> these two methods -- so that we effectively consider both issues in our
> calculations?
> 
> We could also consider the L1A in the inefficiency as well.  However, I'm
> not convinced that the speed at which (or equivalently, the time) a T3
> gets to the L1A is cause for inefficiency. (see the talk I linked at the
> top of the email).
> 
> What do you think?
> 
> Thanks,
> 
> Dave
> 
> 
> -------------------------------------------------
> David Flay
> Physics Department
> Temple University
> Philadelphia, PA 19122
> 
> office: Barton Hall, BA319
> phone: (215) 204-1331
> 
> e-mail: flay at jlab.org
>             flay at temple.edu
> 
> website: http://www.jlab.org/~flay
>               http://quarks.temple.edu
> -------------------------------------------------
> 
-- 
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