[Clas_offline] particle faster than light in simulation?

[Zhiwen Zhao]

Hi, folks.

I have some weird particles in simulation which have speed faster than 
light.

For example, the entry in EVNT bank as below
======================================================
ID: 211  Pmom: 0.444  Mass: -0.123  Charge:   1  Betta: 1.631  Cx: 0.383 
  cy: -0.695  cz: 0.608  X: 0.171  Y: 0.099  Z: -52.628  DCstat:   3 
CCstat:   0  SCstat:   3  ECst
at:   0  LCstat:   0  STstat:   0  Status:   2
======================================================
Everything looks fine except the betta is 1.631. (my target is 40cm long 
and centered around -50cm)

According to the bank definition betta=R_trk/TOF/c
My interpretation is that
betta = sc.path / (sc.time - starttime) / c_light;

from SCPB bank, I got sc.time=7.825, sc.path=545.901
my event starttime is -50/c_light=-1.67
then beta = 545.901/(7.825+1.67)/30=1.9
It can have other vertex correction etc, but the result is confirmed to 
be larger than 1.

So why?

Thanks

Zhiwen