Decay electron events can also be used for the energy calibration. The selection criteria for the decay electron events are described in other section. The energy spectrum of decay electron is
where Ee 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 Neff 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 16N generated by capture of a stopping to an oxygen nucleus in water. The ratio of the peak positions of the Neff 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.
revised on 1999/09/27 email@example.com