From bennett@hpmvd.lanl.gov Thu Dec  3 09:06:42 MST 1998
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Date: Thu, 3 Dec 1998 09:06:42 -0700 (MST)
From: Michael Bennett <bennett@hpmvd.lanl.gov>
Message-Id: <199812031606.JAA27612@hpmvd.lanl.gov>
To: wohn@iastate.edu, sullivan@p2hp4.lanl.gov, young@mail.phy.ornl.gov
Subject: Re:  mvd and level 1
Cc: petridis@iastate.edu, schlei@lanl.gov, jsimon@lanl.gov, hubert@lanl.gov,
        sullivan@p2hp4.lanl.gov
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Hello all,

	In response to Glenn's earlier mail on offline corrections, attached 
below, I agree that an MVD multiplicity trigger uncorrected for vertex leads to 
a messy smearing of actual accepted multiplicity.  In terms of normalizing cross 
sections from this trigger, I don't see having to make an offline correction as 
such a big deal.  Since the acceptance for various processes almost certainly 
varies with vertex position, one would necessarily be applying a vertex 
correction anyway and adding a cut on an offline-corrected multiplicity is 
probably not so difficult.  In the end, one can choose a corrected set of 10% 
central events which contain the process of interest, and arrive at a reliable 
cross section.
	However, I would be more concerned about a vertex-biased MVD LVL1 as an 
input to higher level triggers.  Say, for example, one wanted to trigger on a 
high energy hit in the EMCal; presumably this trigger would normally also 
require a LVL1 trigger to have been formed.  Now the EMCal trigger also carries 
a vertex bias due to acceptance; if the input LVL1 trigger from MVD also carries 
a (different) vertex bias, it seems to me that unfolding all of that to arrive 
at a reliable cross section becomes much more difficult.  I would think that 
anything we can do to make the LVL1 input to higher triggers as unbiased as 
possible would be worthwhile.  
	So, I would agree with John S.'s earlier message, that while an 
uncorrected MVD LVL1 is probably OK to start, it would be a mistake to design 
away the ability to make a vertex correction to the MVD LVL1 in the long run.
	
	
						Regards,
						Mike 
> 
> Dear MVD/LVL1 folks,
>   A question arising from a sudden bout of nervousness, upon reading
> JohnS' note to Fred:
> 
> If John finds a multiplicity signal that is 13 +-4% smaller for a Z
> vertex at +-40cm compared to one at the nominal Z=0, then if
> we implemented a 'centrality' trigger on such information that took
> the supposed 10% most central events, wouldn't we end up with a rather
> messy smearing of the resultant event sample in terms of actual multiplicity?
> 
> Said differently, not having a z-vertex correction to take out such
> "10%-level" effects sounds like a considerable worry, yes?
> 
> If I can get the correction down to 1-2%, then I'm happy to make
> an off-line cleanup cut.  The choice of "1-2%" is subject to the usual
> debate, of course.
> 
> Regards, Glenn


************************************************************
Mike Bennett
P-25 Mail Stop H846 
Los Alamos National Laboratory
Los Alamos, NM  87545

phone:  505-665-2760
fax:    505-665-7920
email:  mjbennett@lanl.gov