## Kaon LT Meetings » grp_22mar04.txt

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Mar 04/22 Group Meeting Notes |

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Participants: Garth, Stephen, Vijay, Ali, Nathan, Love |

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Vijay: |

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- good discussion on how to deal with pion leakthrough in (e,e'K+) analysis |

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Three methods come to mind: |

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1. Histogram subtraction |

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i.e. make a clean pion sample, normalize the pi+n MM peak to the leakthrough |

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to determine the scale factor, and subtract the clean pion sample from the |

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K+ sample to get a clean(er) K+ sample |

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Advantages: |

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- accurately models the pi+Delta0 shape underneath the Lambda and Sigma |

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peaks |

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- once the MM scale factor is determined, in principle this can also be used |

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to clean up focal plane and other observables, for comparison with MC. |

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* Cautions/Suggestions for Future Work* |

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- this method only works if the pion leakthrough fraction is same for pi+n |

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and pi+Delta0 MM regions |

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* Need to investigate the stability of the pi+n/pi+Delta0 ratio |

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vs. CoinTime, RF cuts |

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2. Polynomial subtraction |

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i.e. fit a polynomial to the clean pion MM sample, and use that polynomial |

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(with adjustment) to get a clean K+ sample |

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Advantages: |

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- Vijay shows that this method seems to work for at least one setting |

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*Cautions/Suggestions for Future Work* |

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- need to be sure that the Lambda, Sigma radiative tails are not |

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over-subtracted, as they are an important part of the reaction yield |

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- if this method is used, the best way would be to get the Lambda, Sigma |

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peak shapes from SIMC and use that, in combination with the polynomial, in |

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the fit |

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3. Clean K+ cuts |

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i.e. make a clean (e,e'K+) spectrum by applying tight cuts to eliminate most |

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if not all pion leakthrough |

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*Cautions/Suggestions for Future Work* |

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- almost certainly, this gives a lower K+Lambda yield than methods 1,2 |

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- the lost K+Lambda events would have to be corrected for via a "cut |

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efficiency". It is not immediately obvious on how this efficiency factor |

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would be determined, maybe by comparing with methods 1,2, but in that |

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case, why not just use them for the analysis? |

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- however, a quick comparison of the lower yield from method 3 compared to |

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methods 1,2 could be useful for systematic error determination, for |

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example by setting an upper bound on how large the cut-event-loss effect |

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is |

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Vijay should keep track of this discussion, for use in his further studies |

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