Kaon_LT Experiment

      Meeting to discuss BSA systematic uncertainties calculation

                               24-Apr-02

                             (Notes by GH)

Present

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Regina - Garth Huber, Nacer Hamdi, Ali Usman, Alicia Postuma, Muhammad Junaid,

   Nathan Heinrich, Vijay Kumar

JLab - Dave Gaskell

Ohio - Julie Roche

CUA - Tanja Horn

York - Stephen Kay

Alicia has prepared some slides to guide our discussion.

At present, Alicia calculates the BSA 10 different ways:

                    Full-Fit   Sine-Fit

     Nominal Cuts      A          A'

     Narrow CT         CN         CN'

     Wide CT           CW         CW'

     Narrow MM         MN         MN'

     Wide MM           MW         MW'

For each one, obtain a fitting uncertainty for Sin(phi) term, yielding 10

different values of the BSA and 10 corresponding uncertainties.

The question is how should we calculate A +/-stat +/-syst ?

- right now, taking the error-weighted average of A and A' as the final BSA

  result

Q1: at what stage do we take the weighted average of the Full and Sine fits?

Option 1: calculate error weighted average for every set of cuts, relative to

  the (A and A' average), and use this to calculate delta(CT), delta(MM)

Option 2: average the cut dependences first, not relative to (A and A' average)

Dave: likes Option1 (weighted averages first).  Want to find the systematic

  relative to the final results, not the intermediate results

Julie: you should take the full-fit A as the answer, and use the (A-A')

  difference from sine-fit as a systematic

  - Tanja prefers this too

Garth: since each of the cut study uncertainties include the statistical

  uncertainties resulting in the respective fits, we will likely have to remove

  the raw statistical uncertainty in quadrature from the systematic coming from

  the fits

  - stats do not enter in (A-A'), but it does in the others

Plotting a systematic error band, or double error bars (as Hall B does)?

Dave: prefers double error bars

  - a systematic error band implies that all points move togther, while they

    probably move independently

Plot points at mean -t or central -t?

  - agree that mean -t is better, since the BSA results are not bin centered

Q2: How to calculate error due to cut dependence?

  delta(C)= [ |A-CN|+|A-CW| ]/2

  delta(M)= [ |A-MN|+|A-MW| ]/2

  - Dave: this is how he does it

  - Nacer: many experiments give the RMS of 2,3 variations

  - Garth: likes delta(C), delta(M) separately for errors discussion, but we

    need to give the community an easily understandable way to use our BSA

    data.  For this, suggest to take RMS of (A-A', CN, ..., MW results) as the

    systematic.

Beam Polarization Error:

- all points should move together

- since this is not the dominant uncertainty (smaller than above systematic),

  just add it in quadrature with the others

Good Consensus:

- show A as result

- include RMS of all different variations as a systematic

- show as a double error bar