[Halld-pid-upgrade] Fwd: thoughts after PID session [from Matt]

[Elton Smith]

-------- Original Message --------
Subject: 	thoughts after PID session
Date: 	Mon, 8 Oct 2012 12:53:31 -0400
From: 	Matthew Shepherd <mashephe at indiana.edu>
To: 	Michael Williams <mwill at mit.edu>, Curtis Meyer <cmeyer at cmu.edu>, 
Paul Mattione <pmatt at jlab.org>, "Meyer Curtis A." 
<curtis.meyer at cmu.edu>, "Ito Mark M." <marki at jlab.org>, Eugene Chudakov 
<gen at jlab.org>, Justin Stevens <jrsteven at mit.edu>, Yi Qiang 
<yqiang at jlab.org>, Elton Smith <elton at jlab.org>



Hi all,

It would be a good idea to establish a PID-upgrade mailing list that we can send all mailings to.  Can someone do this?  I expect the emails will only increase in importance over the next month and everyone should be in the loop.

Now that people are aiming to produce a large Pythia sample and we have easy tools for analysis, it would be very interesting to write a generic algorithm to reconstruct as many exclusive final states as possible.  Just go down the list with K, pi and maybe eta and include as many combinations with recoil proton or neutron that conserve strangeness.  For each, do a kinematic fit, vertex, fit, and maybe constrain the pi^0 mass.  For those with a recoil proton you can study requiring or not requiring it.  You can come up with some rudimentary cuts on chi^2, track multiplicity, PID, etc. that work OK.  Then with just the Pythia sample study the signal purity for each of those final states under different PID options.  So, instead of trying to put in some resonance and hand tuning the analysis, you are taking the Pythia-predicted cross sections for the various topologies and seeing how pure the reconstruction is.  This may allow you to notice more broad patterns in PID behavior (e.g., channels with pi0 are worse, reconstructing the proton is always better, etc.)  Even though we do not optimize any one analysis we may be able to compare the benefits of various PID solutions for a wide range of topologies.

(Side note:  Ryan has some code that he has used on CLEO and BES data to reconstruct pretty much every reasonable permutation of ten or less stable hadrons, do kinematic fits, and generate plots.  We have these huge catalogs of ~1000 sets of plots for any final state in various exclusive decays.  This is great when trying to understand detector performance or look for interesting channels to analyze.  Maybe his code can be adapted to Paul's framework.  Ryan also wrote his own framework for BES and CLEO, but hadn't got around to adapting it for GlueX yet.)

Finally, Eugene pointed out that it may be helpful to explore trying to degrade our resolution in the MC somehow.  My instinct is that the signal purity Paul gets by reconstructing the proton and doing kinematic fitting is too good.  (Every experiment I've worked on required that the resolution be degraded in MC to get chi^2 distributions that match data for kinematic fitting.)  The danger is that people conclude we don't need to PID system because our signal purity is so good with just kinematic fitting.  This is really bad if our MC is too good.  We have to think of some justifiable quantitative way of degrading the MC resolution so it doesn't look like we're just trying to make an excuse for building a PID system when our simulation is telling us otherwise.

Matt




-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://mailman.jlab.org/pipermail/halld-pid-upgrade/attachments/20121008/7029093a/attachment.html