Correlation between generated muons

[jrquirk]

Time for events is always since the primary muon is generated, and primary muons are considered different Geant events. A correlation between muons may be necessary down the road, though it doesn't seem pressing now.

What I did before is just accumulate time while sampling from an exponential (exp[-t * R], where R is the beam rate) and then when t > 110 ms, reset.