Sign of the beam polarization

• Notes on the sign of the beam polarization as determined by the Moller.

Asymmetry at 90 degrees in the Center of Mass:

[N(parallel) - N(anti-parallel)]/[N(parallel) + N(anti-parallel)] = -7/9

Moller solenoid field points DOWNSTREAM, so magnetic moments of electron in iron foil also point DOWNSTREAM.

Magnetic moment of electron given by:

\vec{mu} = (g*e)/(2*m*c) \vec{s}

Electron has negative charge, so spin is in opposite direction of magnetic moment. So spin of polarized electrons in Moller target point UPSTREAM.

• Beni Zihlman's note on the sign of the helicity from the Moller: (ps, pdf)