# 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. Spin of polarized electrons in Moller target point UPSTREAM.

Experimental Moller asymmetry:

A_DAQ = [h+ - h-]/[h+ - h-]


A_Moller<0, h+ denotes beam electrons polarized in the SAME direction as target spin: UPSTREAM

A_Moller>0, h+ denotes beam electrons polarized in the OPPOSITE direction as target spin: DOWNSTREAM

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