[d2n-analysis-talk] Triggers Revisited

[David Flay]

Hi all,

I've been having helpful and insightful discussions with Kalyan and Brad
discussing how the triggers work:

In particular, I was discussing the variables DL.LTN, DL.bitN with Kalyan
over the past few days, and he was telling me that LTN refers to the TDC
of the trigger before the L1A, while bitN corresponds to TN after L1A such
that it refers to the time trigger N arrives at L1A (essentially, also,
bitN is the prescaled version of LTN).  In the case that ps=1, the ratio
of the number of events indicates the livetime (so the deadtime would be 1
- livetime).

This also implies that we have the (general) formula:

N(unprescaled) = ps*N(prescaled)

So, if we have a trigger prescaled to some value, we may do a sanity check
of the LTN and bitN variables to make sure they're consistent.

The same may be said of the BB variable DL.tN (DBB.tN).

Also, for reference, Matt has posted a description of the triggers.  See:

http://www.jlab.org/~posik/d2n/trigger/Trigger_Setup.txt

The T3 trigger is  S1.and.S2, while T4 refers to the LHRS efficiency -- in
particular (from Brad):

"T4 allows you to answer the question:  what fraction of real electrons
(pions, whatever) fail to fire both S1 and S2 and initiate a production
trigger (T3 in our case).  In an ideal world 100% of the good electrons
should fire both S1 and S2, and thus generate a T3.  In the real world
that number is somewhat less than 100%.

T4 lets us measure that trigger (in-)efficiency."

This may be seen in the plots I made for T4 (attached).  The ratio of the
number of events in bit4 to that of LT4 give us the T3 trigger
inefficiency (since, for this run 20675, the prescales for T3,T4 are set
to 1, as confirmed in:
http://www.jlab.org/~adaq/halog/html/0903_archive/090314032136.html)

This gives: 110/1889 ~ 5.8%, which seems reasonable.  Looking at the LT3,
bit3 plots, we see the number of events are virtually identical; however,
shouldn't the inefficiency of T4 be reflected in the numbers we see in
LT3, bit3?

Concerning the linearity or correlation between the LTN and bitN
variables, I have a plot attached, and useful comments from Brad:

"...you will get a constant TDC value for trigger TN if trigger N
generates the L1A.  I would expect to see a single bin (ie. at some fixed
value of DL.LT3 and DL.bit3)... The vertical line tells you that the the
bit3 timing is fixed relative to the L1A (ie. it looks like a T3 generated
L1A), but the DL.LT3 is scattered around..."

(This is best seen in the last plot.)

It should also be noted that we should be aware of the multi-hit
capability of the TDCs and that the LTN, bitN variables are 6-dimensional
arrays.

Dave

-------------------------------------------------
David Flay
Physics Department
Temple University
Philadelphia, PA 19122

office: Barton Hall, BA319
phone: (215) 204-1331

e-mail: flay at jlab.org
              david.flay at temple.edu

website: http://www.jlab.org/~flay
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