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Re: Fwd: Kfit with timing
Hall D PID Mail List:
On Mon, 24 Mar 2008, Matt wrote:
Dear matt,
what I'm saying is that at this stage of the experiment/tracking we have
no idea how well we will be able to control our errors and systematics,
such the suppression factors shown depend on this.
I love MC but I'm sure we will have some effects we will have to include
if we are running which we have no idea about now.
So I just want to make sure we are careful wit hthe numbers we quote that
is all.
bye elke
> Date: Mon, 24 Mar 2008 10:53:53 -0400
> From: Matt <bellis@ernest.phys.cmu.edu>
> To: Elke-Caroline Aschenauer <elke@jlab.org>
> Cc: Alex Dzierba <dzierba@indiana.edu>, Eugene Chudakov <gen@jlab.org>,
> halld-pid@jlab.org, cmeyer@ernest.phys.cmu.edu
> Subject: Re: Fwd: Kfit with timing
>
> Hi Elke,
>
> The only thing which still worries me a bit is the assumptions on the
> > error matrix for the tracking. I think we should show one or 2 example for
> > the kinematic fits, but should clearly point out that this is still a
> > point of concern.
> >
>
>
> I'm not sure I understand the point you keep trying to make when you say
> "point of concern". You're basically saying if we don't understand our
> errors, then the procedure doesn't work. I completely agree with you and
> this was an issue with CLAS. A number of groups tried to build a consistent
> kinematic fitter and failed because the error matrix returned from tracking
> was wrong. It wasn't until Curtis and Mike Williams made a detailed,
> systematic study of these errors that it started to work. In retrospect, the
> study they did could've been done much earlier in CLAS' lifetime, but it
> just wasn't given priority. One thing which I've emphasized from the first
> talk I gave on this to the group last May, is that when we take data we will
> need to have a concentrated effort to understand our error matrix as
> returned by tracking.
>
> *Everything* we will do in GlueX will require a thorough understanding
> of the systematics and errors of both the detector and simulation, and this
> aspect of the analysis is no different. We shouldn't be trying to make these
> first Monte Carlo studies with a broken error matrix, because we would not
> expect to do analysis on real world data with a broken understanding of the
> detector. It definitely warrants a bullet in any of these talks, not so much
> to emphasize the problems, but to emphasize we know what we are doing and
> that we understand what studies we will need to do in the early calibration
> days of GlueX. The kinematic fit and it's usage should be considered no
> different from any other aspect of our PID or reconstruction (pattern
> finding, cluster algorithms) and we should expect as much effort to be put
> into it's understanding as anything else in the experiment.
>
> The fact that the effective usage of the kinematic fit relies on our
> understanding of the error matrix should be no more a "point of concern"
> than any any other part of the reconstruction.
>
>
> --
> --
> ----------------------------
> Matt Bellis
> Carnegie Mellon University
> (office) 412-268-6949
> (cell) 412-310-4586
> ----------------------------
>
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