The PDF is Gaussian function.

The rms has beeen set at 1.69 mm to match
the standard deviation of the data z0 histogram
with theta=90 deg cut - the rms value 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.