From sullivan Wed Dec  2 17:59:01 MST 1998
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From: John Sullivan <sullivan>
Message-Id: <199812030058.RAA28637@p2hp4.lanl.gov>
Subject: mvd and level 1
To: wohn@iastate.edu (Fred Wohn)
Date: Wed, 02 Dec 1998 17:58:56 MST
Cc: sullivan, hubert@lanl.gov (Hubert van Hecke),
        jsimon@lanl.gov (Jehanne Simon-Gillo), schlei@lanl.gov (Bernd Schlei),
        mjbennett@lanl.gov (Mike Bennett),
        young@orph01.phy.ornl.gov (Glenn Young),
        petridis@iastate.edu (Athan Petridis)
X-Mailer: Elm [revision: 212.2]
Status: RO

Hi Fred (with copies to other possibly interested parties),

  I did a short study of the variation in the number of
strips above threshold in the MVD (this times something
like 50mV is what goes from the mvd to level 1 for a trigger).
I have received several emails, directly and indirectly,
about level-1's ability to find the vertex. One of them
said you see little variation in the mvd trigger signal
with the vertex position. You also told me this in person
in Santa Fe. If I ever knew, I have forgotten what the
variation was quantitatively. I did a calculation and
found the multiplicity signal to level 1 is 13+-4% smaller
for a vertex at +-40cm compared to z=0. I do not know
whether or not to classify this as significant. 

   My own thinking is that it would be acceptable to
ignore this correction in the first version of the
trigger. However, I do no think it is a good idea to make
an irrevocable decision to skip the z vertex correction.
One reason for this is that the variation in the multiplicity
with the vertex position depends on the shape of dN/deta -- 
which is currently unknown.  What if it varies enough with
impact parameter to cause trigger trouble? A double-peaked
distribution at medium impact parameters could cause the
trigger to prefer medium impact parameters at vertex positions
far from the center. In a year or so we will know the answers
to these questions and could make much more informed 
decisions.

  The summary of my results is on the web:
http://p25ext.lanl.gov/people/sullivan/notes/phenix/trigger/trig_vs_zvert.html
Local people saw some of this stuff today. I have added
a few plots since then.

Regards,
John