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

Mon Oct 8 17:58:06 EDT 2012

Matt, OK, that makes sense.   The question was asked about when the O(100M) bkgd events were being discussed.   Curtis said something about the time being short to get this ready for the meeting so (having not heard any of the questions themselves, just the answers) I thought maybe some material interactions were turned off in GEANT to speed up the bkgd sample generation time.   Clearly that would make a big difference but wouldn't be a crazy thing to do just to get some "sanity" initial numbers in a super hurry.   Anyway, I now see what was done so just ignore the original comment.

Paul, I mean that if I want to look at gp -> p X, X -> whatever in GlueX, I want a uniform acceptance in the variables of interest in the "whatever" final state.   Whether or not I detect the proton is correlated with the kinematics of X.  So, in the 2 samples (p reco'd and p ignored) the kinematics of X are different (or can be) and, thus, the efficiencies in the variables of interest in "whatever" could be different.    Maybe GlueX is hermetic enough for this not to matter ... but it could so we should at least check.

Also, I don't know how much non t-channel is an issue at GlueX (or how people plan on dealing with it) but requiring you detect the proton will certainly affect the acceptance in t (reducing it more where the t-channel is the most dominant).  Maybe this also isn't an issue but it could be so I ask ;-)

One final question: Do we have any decent predictions for the size of the hybrid rates?  Paul is looking at S/B but we don't really care about S, we care about S*f where f is the fraction of the signal that is from a hybrid.   If the bkgd is of comparable size to the hybrid contribution, then it could be a problem (regardless of how big the non-hybrid signal is).

Mike

On Oct 8, 2012, at 5:18 PM, Paul Mattione wrote:

The studies of different topologies, particles, etc. should be easy to do and standardize in the analysis framework.

Mike, what efficiencies are you referring to regarding whether the proton is required?  What do you mean by flatness?  The Signal / Background ratios and % of signal loss due to requiring that the kaons not be pions are included on the slides.

 - Paul

On Oct 8, 2012, at 4:29 PM, Elton Smith wrote:

-------- Original Message --------
Subject:        Re: thoughts after PID session
Date:   Mon, 8 Oct 2012 18:02:31 +0000
From:   Michael Williams <mwill at mit.edu><mailto:mwill at mit.edu>
To:     Matthew Shepherd <mashephe at indiana.edu><mailto:mashephe at indiana.edu>
CC:     Curtis Meyer <cmeyer at cmu.edu><mailto:cmeyer at cmu.edu>, Paul Mattione <pmatt at jlab.org><mailto:pmatt at jlab.org>, "Meyer Curtis A." <curtis.meyer at cmu.edu><mailto:curtis.meyer at cmu.edu>, "Ito Mark M." <marki at jlab.org><mailto:marki at jlab.org>, "Eugene Chudakov" <gen at jlab.org><mailto:gen at jlab.org>, Justin Stevens <jrsteven at mit.edu><mailto:jrsteven at mit.edu>, Yi Qiang <yqiang at jlab.org><mailto:yqiang at jlab.org>, Elton Smith <elton at jlab.org><mailto:elton at jlab.org>

Hi Matt,

Sounds good.

Paul, did I hear correctly that material interactions are not included in the study so far?  Pretty important ... if not b/c of time constraints so far that's totally understandable ... but pretty important to have this in before making any decisions (or showing to any external people).

For MC vs data resolution I guess the following two "laws" hold: (1) the real alignment will never be perfect, especially for one subsystem w.r.t. another and (2) there is always more material where material isn't measured then expected.   Law (1) can probably be expected to reduce our resolution by 10%.  Law (2) seems to always hold for things like glue where nobody measures it when using it and simulations tend to be based on some ideal minimum amount required to hold things together (although why one expects the undergrads doing the glueing to achieve this minimum I don't know).    I don't think anybody would complain if we simply assumed 10-20% less than ideal resolution for the PID studies ... we can say "based on all experiments ever run" ;-)

Anyway, I totally agree that more channels is better.  There will be correlations b/t what's in the final state and how important the PID is and it'd be good to know what these are.   Are you including KS, Lambda, Sigma in this list?  The KS will be used I'm sure.   If we're interested in hybrids with open strangeness I would assume they are often times produced with Lambdas and Sigmas.    These topologies help on their own (displaced vertex) but still worth looking at how PID helps here if we're interested in these channels.

Another question I had (maybe this is obvious if you've been looking at GlueX MC for years) was how much different (mainly in "flatness") the efficiencies are when the proton is required vs ignored?  Does it matter?  For PWA S/B isn't the only metric.    Also, for honesty's sake, does requiring that the kaon is hard enough to pass the PID hurt the uniformity of the efficiency?   The channels we've looked at have a very hard kaon nearly 100% of the time so not an issue there but it is something worth considering.

Cheers,

Mike

On Oct 8, 2012, at 12:53 PM, Matthew Shepherd wrote:

>
> 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 behav
 ior (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

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