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At the elementary level, the weak force is composed of a ‘charged current’ and a ‘neutral current’ mediated by the W± and Z0 bosons, respectively.

The decay of the meson to two muons, shown in Fig. 1c, is forbidden at the elementary level because the Z0 cannot couple directly to quarks of different flavours, that is, there are no direct ‘flavour changing neutral currents’.

Its discovery would verify the existence of a complex scalar field thought to give mass to three of the carriers of the electroweak force—the W+, W–, and Z0 bosons—as well as to the fundamental quarks and leptons.

The former is the number of arc degrees from the horizon to the moon's center; therefore Z0 is readily obtained by subtracting the altitude from 90°.

The value of r0 will in general vary with z0; what is in most cases of importance is the question whether the lower limit of r0 for all positions is zero or greater than zero.