Home » PANDA » PandaRoot » Monte Carlo Engines » Group velocity for Cherenkov photon propagation in G3/G4
| Re: Group velocity for Cherenkov photon propagation in G3/G4 [message #11462 is a reply to message #11459] |
Wed, 26 January 2011 17:41   |
Jochen Schwiening
Messages: 85
Registered: June 2009
Location: GSI, Darmstadt
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continuous participant |
From: *gsi.de
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Hi Mohammad,
thanks for the suggestion.
I used TrackLength() and TrackTime() in PndDrc to calculate
the photon velocity in the bar at several times in the
Cherenkov photon's life. What I see is that the apparent
velocity does not behave as I expect. Here's an example for
two photons in Geant3 in the same event as they pass their
30ns mark:
time: 30.1524, path: 532.029, velocity: 17.6447, energy: 4.16593, wavelength: 296.971
time: 30.0086, path: 537.002, velocity: 17.8949, energy: 1.5531, wavelength: 796.575
This is probably because the TrackTime() of the photon includes
the time of flight of the primary particle. If I manually
calculate the time of flight of the primary particle and
subtract it I get velocity values around 19cm/ns, closer to
the expected values.
To illustrate the point I plotted (in excel, sorry) the observed
velocity vs wavelength for a few hundred photons in G3 and in
G4 as well as the expected group velocity. Please see the
attached figure.
Would you have a suggestion how I can access in PndDrc.cxx
the TOF of the particle and subtract it?
And is TrackLength() a "clean" quantity, which contains only
the path inside the bar? Or do I need to make a correction to
get the path that corresponds to the corrected TrackTime()
value I need to use?
Thanks,
Jochen
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