W-ZED

W-ZED is not weak. He is heavy, which from a distance looks the same.

The W boson carries the charged weak interaction, which turns a down quark into an up quark and a neutron into a proton, electron and antineutrino. Its coupling to matter, g, is not small: it is comparable to the strength of electromagnetism. What makes the force feeble in everyday processes is the second formula on this page. Fermi's constant, which sets the rate of beta decay, goes as g² divided by the W mass squared. At low energies a W is so expensive to borrow that the interaction rarely happens, which is why a free neutron survives about fifteen minutes. (The exact figure is itself disputed between two kinds of measurement.) The mass also sets the range, the third formula: about 2.5 × 10⁻¹⁸ metres, a few hundred times smaller than a proton.

The W itself does not last. Its decay width is about 2.1 GeV, which means a lifetime near 3 × 10⁻²⁵ seconds. At CERN in 1983 the UA1 experiment found it through its decay products: a single energetic electron plus missing momentum, carried off by an unseen neutrino. Carlo Rubbia and Simon van der Meer shared the 1984 Nobel Prize. Sheldon Glashow, Abdus Salam and Steven Weinberg had predicted the W, with the Z, in electroweak theory, and shared the 1979 prize.

One number is unsettled. PDG's 2024 world average for the W mass is 80.369 ± 0.013 GeV. In 2022 the CDF experiment at Fermilab reported 80.434 ± 0.009 GeV, heavier than the Standard Model expects and in tension with the other measurements, and PDG leaves it out of the average. Whether CDF saw new physics or an unrecognised error is open.

W-ZED arrives mid-event and leaves before it ends.