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Kaon LT Meetings » bsa_24apr02.txt

Garth Huber, 04/02/2024 06:46 PM

 
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      Meeting to discuss BSA systematic uncertainties calculation
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                               24-Apr-02
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                             (Notes by GH)
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Present
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-------
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Regina - Garth Huber, Nacer Hamdi, Ali Usman, Alicia Postuma, Muhammad Junaid,
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   Nathan Heinrich, Vijay Kumar
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JLab - Dave Gaskell
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Ohio - Julie Roche
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CUA - Tanja Horn
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York - Stephen Kay
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Alicia has prepared some slides to guide our discussion.
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At present, Alicia calculates the BSA 10 different ways:
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                    Full-Fit   Sine-Fit
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     Nominal Cuts      A          A'
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     Narrow CT         CN         CN'
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     Wide CT           CW         CW'
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     Narrow MM         MN         MN'
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     Wide MM           MW         MW'
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For each one, obtain a fitting uncertainty for Sin(phi) term, yielding 10
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different values of the BSA and 10 corresponding uncertainties.
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The question is how should we calculate A +/-stat +/-syst ?
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- right now, taking the error-weighted average of A and A' as the final BSA
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  result
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Q1: at what stage do we take the weighted average of the Full and Sine fits?
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Option 1: calculate error weighted average for every set of cuts, relative to
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  the (A and A' average), and use this to calculate delta(CT), delta(MM)
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Option 2: average the cut dependences first, not relative to (A and A' average)
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Dave: likes Option1 (weighted averages first).  Want to find the systematic
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  relative to the final results, not the intermediate results
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Julie: you should take the full-fit A as the answer, and use the (A-A')
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  difference from sine-fit as a systematic
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  - Tanja prefers this too
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Garth: since each of the cut study uncertainties include the statistical
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  uncertainties resulting in the respective fits, we will likely have to remove
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  the raw statistical uncertainty in quadrature from the systematic coming from
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  the fits
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  - stats do not enter in (A-A'), but it does in the others
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Plotting a systematic error band, or double error bars (as Hall B does)?
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Dave: prefers double error bars
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  - a systematic error band implies that all points move togther, while they
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    probably move independently
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Plot points at mean -t or central -t?
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  - agree that mean -t is better, since the BSA results are not bin centered
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Q2: How to calculate error due to cut dependence?
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  delta(C)= [ |A-CN|+|A-CW| ]/2
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  delta(M)= [ |A-MN|+|A-MW| ]/2
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  - Dave: this is how he does it
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  - Nacer: many experiments give the RMS of 2,3 variations
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  - Garth: likes delta(C), delta(M) separately for errors discussion, but we
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    need to give the community an easily understandable way to use our BSA
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    data.  For this, suggest to take RMS of (A-A', CN, ..., MW results) as the
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    systematic.
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Beam Polarization Error:
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- all points should move together
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- since this is not the dominant uncertainty (smaller than above systematic),
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  just add it in quadrature with the others
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Good Consensus:
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- show A as result
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- include RMS of all different variations as a systematic
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- show as a double error bar
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(400-400/430)