[Halld-offline] Questions on b1pi histograms

[Mark M. Ito]

Sounds complicated.

Trying to think what the purpose of this test is...

On 05/15/2013 03:30 PM, Paul Mattione wrote:
> During the offline meeting there were some questions regarding the contents/meaning of the b1pi histograms (e.g. https://halldweb1.jlab.org/b1pi/2013-05-13/Linux_CentOS6-x86_64-gcc4.4.6/).  I've done some digging through the scripts/software and here are some answers:
>
> # Reconstructed Photons: Just because a neutral shower is not matched to a track doesn't mean it's a photon.  When making these diagnostic histograms (the DHistogramAction_DetectedParticleKinematics action) the software tries to determine the PID (for all particles) by:
> 1) Matching to Thrown Particles: If the reconstructed particle is matched to a thrown particle, it uses the thrown PID (the matching algorithm may not be ideal, but it works well enough for now).
> 2) PID FOM: If it can't find a thrown particle (e.g. ghost track or part of a non-fully-clusterized hadronic hit in the calorimeter), it uses the PID with the highest confidence level (for showers, this is done by delta-t: (Shower_Time - Flight_Time) - RF_Time).  However, this PID is cut at 10^-5, so if it's less than that it will be classified as "Unknown" and will not be histogrammed.  This is why there are less histogram entries than neutral showers (neutron PID FOM is fixed to -1).
>
> # Reconstructed Pi0's: The peak is there, it's just swamped by background.  At the point when this histogram is made, a cut has already been placed requiring that at least 4 charged particles (2+, 2-) be reconstructed.  That's why there's a lot fewer pi0's than you'd otherwise expect.  Also, a PID cut has been placed on these other tracks.  Also, the # printed in the histogram is just the # of histogram entries, which includes the massive background.
>
> # Reconstructed Resonances: The counts in these histograms are different due to double-counting considerations.  For example, there are roughly 4x the number of entries in the omega histogram than in the pi0 histogram.  This is because the pi0 histogram doesn't care which charged particles are in the combination, it only cares about the photons.  So if you detect 2g, 2pi+, 2pi- you would have 1 entry in the pi0 histogram but 4 entries in the omega histogram, depending on which of the pions are chosen.
>
> Also, currently the mass peaks are histogrammed prior to kinematic fitting, so I'm now going to change it so that it histograms the mass peaks after kinematic fitting (and a cut on the confidence level).
>
>   - Paul
>
>
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