where *E*_{e} is decay electron energy, *G* is Fermi coupling constant, and is muon mass.
The maximum energy of a decay electron is 53MeV, and the mean energy is 37MeV.

Fig 1 shows
*N*_{eff}
distribution of observed decay electron events both in measurement and
in Monte Carlo simulation. The measured and Monte Carlo data are consistent except for
very low energy region. The difference of low energy region is caused by a gamma ray
emission from radioactive nuclei such as ^{16}N generated by capture of a stopping to an oxygen
nucleus in water. The ratio of the peak positions of the *N*_{eff} distributions between the
measured and the Monte Carlo data is as follows,

.

This confirms that energy scale measured by decay electron event is reproduced by Monte
Carlo to within 1.2%, with no observed position dependence.