Electrons
and Mirror Symmetry
The neutral
weak force between an electron and a target particle, mediated by the Z
boson, can be isolated by measuring the fractional change under a mirror
reflection of the scattering probability of relativistic longitudinally
polarized electrons off unpolarized targets. This technique yields neutral weak
force measurements at a length scale of 1 femtometer, in contrast to high
energy collider measurements that probe much smaller length scales. Study of
the variation of the weak force over a range of length scales provides a
stringent test of theory, complementing collider measurements. We describe a
recent measurement of the neutral weak force between two electrons by the E158
experiment at the Stanford Linear Accelerator Center. While the weak force between an electron and
positron has been extensively studied, that between two electrons had never
directly been measured. We conclude by discussing prospects for even more
precise measurements at future facilities.