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Forum: Electromagnetic Processes
Re: Question why polarization vector is not perpendicular to momentum ?
Date: Sep 30, 13:35
From: Andreas Schaelicke <Andreas Schaelicke>

Dear zhangyf,

The definition of polarization differ for LowEnergy and Standard processes.

In LowEnergy the direction of the electric field is specified, which is sufficient if you are only interested in linear polarisation. This vector is perpendicular and of unit length. This is probably what you are refering to.

On the other hand, the Std Polarized processes (e.g. G4PolarizedCompton) use the Stokesvector. This way it is possible to treat also circular polarisation, but implies a different meaning of the polarisation vector. The stokesvectors are defined in a local "Particle Reference Frame". For example (0.,0.,-1) is a 100% circularly polarised (particle physists left-handed), independent of the direction of the particle. Also polarisation is interpreted in a probabilistic manner, e.g. (0.,0.,0.5) means 50% cicular polarisation For transformation of polarisation between different frames some helper functions are available in G4PolarizationHelper.

In the linked files you can find results, and polarization vectors for a Compton simulation with LowEnergy package and with Standard for a photon in +z-direction.

comptonLIN1.pdf
comptonLIN2.pdf

Best regards,
Andreas

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1 Ok: Re: why polarization vector is not perpendicular to momentum ?   (zhangyf@ihep.ac.cn - Oct 08, 08:38)
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