The PDF is Landau function with C=605.5, MPV=2.1532, sigma=1.8978.

The resultuon has beeen set to match
the standard deviation of the data z0 histogram
with theta=90 deg cut - the rms value of Michel events 
at tht=90 was derived by extrapolating the values for 
fabs(theta-90)<15,10,5 deg.

The pi+ momentum was 76.6MeV +- 1.0MeV.