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Re: Group velocity for Cherenkov photon propagation in G3/G4 [message #11459 is a reply to message #11457]

Wed, 26 January 2011 14:12

Jochen Schwiening
Messages: 85
Registered: June 2009
Location: GSI, Darmstadt

continuous participant

From: *gsi.de

Hi Stefano,

thanks for the quick response.

I know from past work with (standard, non-Panda) Geant4 that
G4 does in fact use the wavelength-dependent photon group
velocity to calculate the propagation time. It uses the
formula n_group = n_phase - lambda*(dn_phase/dlambda).
It even comes out at the correct values, about 19.1cm/ns for
300nm photons, 20.3cm/ns for 600nm photons.
My quick and dirty check in our Panda simulation data finds
almost constant values of 19cm/ns +-0.1ns/cm for the entire
wavelength range from 300-650nm.

I don't think that I know how to find out in ProcessHits in
PndDrc.cxx how far the photon traveled since the path is
defined by the many internal reflections. We instead calculate
the path from the photon production angle and then calculate
the velocity from this path and the photon propagation time.
It's possible that this code has a bug and that's why I would
like to debug the (group) velocity of the photon in the medium
using something like the GetVelocity function but I don't see
that in our VMC environment.

Any other (simple) way to check the photon speed?

Thanks,
Jochen

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[Message index]

		Group velocity for Cherenkov photon propagation in G3/G4 By: Jochen Schwiening on Wed, 26 January 2011 11:46
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: StefanoSpataro on Wed, 26 January 2011 12:41
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Jochen Schwiening on Wed, 26 January 2011 14:12
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: StefanoSpataro on Wed, 26 January 2011 14:37
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Mohammad Al-Turany on Wed, 26 January 2011 14:53
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Jochen Schwiening on Wed, 26 January 2011 17:41
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Jochen Schwiening on Thu, 27 January 2011 11:33
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Oliver Merle on Fri, 28 January 2011 19:04
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Mohammad Al-Turany on Wed, 26 January 2011 21:23
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Jochen Schwiening on Fri, 28 January 2011 19:14
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Oliver Merle on Fri, 28 January 2011 19:39
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Jochen Schwiening on Fri, 28 January 2011 21:33
		Re: Group velocity for Cherenkov photon propagation in G3/G4 By: Jochen Schwiening on Mon, 11 April 2011 15:25

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