J-PARC Experiment E36 at the Nuclear and Particle Physics Facillity

Precise Measurement of Γ (K+→ e+ν)/Γ(K+→ μ+ν)
using Stopped Positive Kaons

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Calibration of the detector performance

Purpose for taking the calibration data

One of the most essential points of this experiment is the estimate of the Ke2 and Kμ2 acceptance of the detector. It is very relevant to the stopped K+ method of the proposed experiment, in which the acceptance is primarily determined by the finite solid angle of the detector system in contrast to the in-flight decay experiments where there is no such constraint but issues of difficult kinematical separation exist.

We will perform a full Monte Carlo simulation based on a reliable code, and that the validity of the simulation can be checked against existing data of various observables (not necessarily the acceptance itself) from KEK-PS and possibly with E36 data. While we cannot avoid relying partially on Monte Carlo simulations, it is desirable to support the calculations of the acceptances using data. We discuss the various possible methods to estimate the acceptance ratio using the existing data or future calibration data from E36. This gives us a more reliable estimate of the associated uncertainties.

Calibration of PID performance

It is clear that particle mis-identification introduces an additional uncertainty for the RK determination. In order to check the performance of the particle identification by the TOF and AC system, the mis-identification probability will be directly measured using the experimental data. Here, the PGC system is available and it will help to confirm the particle identification for this calibration purpose. The probability of the e+ inefficiency and the τ+ misidentification by the AC counter can be measured by comparing the AC signals with the TOF and PGC information. It is to be noted that four-point tracking can be used for this study. By changing the combination of the detectors and repeating the calibration, we can check the performance of all three detectors.