## Particle spin in decay

In experiments with polarized beams of particles, I suppose one knows the spin orientation probabilities of those particles, is that the case?

When physicists make experiments with polarized beams of unstable particles, how do they treat spin in a decay of such a polarized particle? If the spin polarization vector of particle before decay is known, can they determine spin polarization of decay products?

For example in a polarized beam of muons $\mu^+$ with a given spin polarization ${\bf S}=(S_x,S_y,S_z)$ decays into three particles, e.g. $\mu^+\to\nu_\mu e^+\bar{\nu}_e$, could the polarization vector of positron be determined?

Or maybe this image is totally wrong!?

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 Blog Entries: 1 Recognitions: Science Advisor Not sure what you're asking. In an experiment with a polarized beam of particles, the scattering will be asymmetrical, and this is what we study. To determine the polarization of the scattered particles, you need to scatter them again off something else, i.e. a double scattering experiment.
 Thanks Bill. Is it correct that for a polarized beam you know the spin polarization vector of particles ${\bf S}=(S_x,S_y,S_z)$, where these components are probabilities for a measured spin to be in that direction? When a beam is scattered from a target sometimes particle's spin is also measured on the detector, i suppose one measures particle's spin polarization here. If that's the case I was wondering if such a particle flying away from the target would decay, could its spin polarization be calculated from the measure polarization of decay products. Can you suggest some article/book on these polarized experiments? As you can see this is new to me :)

## Particle spin in decay

Are you interested in experiments with polarized beams like SLAC $e^{+}e^{-}$ experiments in the 90`s or in the dynamics of decay of polarized particles?

 Yes, it's the dynamics of decay of polarized particles that interests me.
 Usually when a polarized particle decays, the most useful way to determine its polarization is mesaruing the direction of motion of its decay products in its rest frame and not the polarization of its decay products ( usually very hard to measure). For example the measurement of W boson polaroization from top decays uses the direction of motion of the charged lepton from its decay http://arxiv.org/abs/1205.2484

 Tags decay, particle, polarized, spin