From: murray@comp.tamu.edu
Date: Tue Nov 19 2002 - 16:37:03 EST
Dear Claus,
your scheme seems very resonable. Do you plan to decide
weather a given track is a pion, or a kaon, or a proton? An alternative
is to statistically identify each track and say that it is 85% a pion,
14% a kaon and 1% a proton. If one cuts in "orthogonal" variables such
as mass**2 and confidence level of the track then the total efficency is
just the product of the indivdual efficencies. These are surely best
evaluated from the fits and often leave some room for interpreation.
This whiggle room ends up in your systematic error. If one does cuts
in variables that are correlated things are a lot harder.
However the efficecies can be evaluated from histogrammes after all
of your loops.
YOurs Michael
Quoting "Claus O. E. Jorgensen" <ekman@nbi.dk>:
>
> Hi analyzer,
>
> After some correspondence on the analysis of the dbsts I have
> now written up some thoughts on how to get on with the analysis
> from the bdsts. The ambition is to end up with some kind of
> standard analysis method in the future.
> As Jens-Ivar pointed out this discussion should be on the dev-list
> and as Flemming pointed out we should (think a bit and) agree
> before we do the coding (thanks for the comments).
>
> What we want to do:
>
> - Select events
> - Select good tracks
> - Identify particles
> - Evaluate efficiencies
> - ???
>
> I like the way it is done in the Bdst{Mrs,Fs}Ana (the new versions of
> Br{Mrs,Fs}DstAna) modules. The basic idea is to scan the data and
> determine various constants for event selection, momentum
> determination, track selection and pid selection (in the code these
> scans is called the prepreloop and preloop). The found constants are
> then used when selecting events, tracks and identified particles in the
> final loop over all events and tracks.
>
> What are these constants and how are they determined?
>
> Event Selection:
>
> - Difference in bb and zdc vertex (mean and sigma).
> Determined by fitting a simple histogram (bbVtxZ - zdcVtxZ)
> which is filled in the preloop.
> A nSigma cut can then by applied in the "real" loop.
>
> - Vertex range. Set by the user.
>
> - Centrality range. Set by the user.
>
> - Good trigger.
>
>
> Track Selection:
>
> - Track to vertex (meanZ, sigmaZ, meanY, sigmaY)
> Determined by fitting histograms filled in the preloop.
>
> - Good track status.
>
> - Fiducial cuts?
>
>
> Pid Selection:
>
> - Constant determining the expectation curves (for example mass2)
> for each particle for each pid detector. Found by fitting
> histograms filled in the preloop.
>
> - Sigma from expectation curve (momentum dependent).
>
> We can maybe have a method that return the number of sigmas from
> the expectation curve for a given particle specie, or?
> I don't think there's anything wrong in "fine-tuning the
> calibrations" at this point (the alternative is several iterations
> of the calibrations to get the 100% correct values).
>
> Efficiency:
>
> - Pawel is the expert in this and I'll not try to describe it, but
> I think it should be in a separate module.
>
> This stuff described above is actually not so far from what is in
> the code now. Maybe we can split the tasks into several modules, or?
> I would like to try to put the skeleton together, then we can always
> discuss the details...any comments or suggestions?
>
> How can we implement the pp (or d+Au) in such a framework? How do want
> to pass on the information (at this point it's saved in a ntuple which
> adds another step in the analysis chain)?
>
> Cheers,
>
> Claus
>
> +------------------------------------------------------------+
> | Claus E. Jørgensen |
> | Cand. Scient. Phone : (+45) 33 32 49 49 |
> | Cell : (+45) 27 28 49 49 |
> | Niels Bohr Institute, Ta-2, Office : (+45) 35 32 54 04 |
> | Blegdamsvej 17, DK-2100, E-mail : ekman@nbi.dk |
> | University of Copenhagen Home : www.nbi.dk/~ekman/ |
> +------------------------------------------------------------+
>
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