The weak mixing angle

I thoroughly enjoyed reading Konrad Kleinknecht’s excellent summary of Jack Steinberger’s life and physics career (Physics Today, September 2021, page 59 ). I was unaware of several of Steinberger’s achievements. In my opinion, he deserved additional Nobel Prizes for some of them, such as his calculation of the two-photon decay rate and lifetime of the neutral pion and discovery of ${\mathrm{K}}_{\mathrm{L}}^0$ leptonic decay’s CP-violating charge asymmetry.

I would like to point out, however, that the Weinberg angle, ${\theta }_{\mathrm{W}}$, referred to in the obituary is also called the “weak mixing angle.” It was invented by Sheldon Glashow in his famous 1961 paper, “Partial-symmetries of weak interactions.” It is the angle that diagonalizes the 2 × 2 matrix of the neutral gauge bosons, giving the Z boson and the photon as the mass eigenstates in the model based on the gauge group SU(2) × U(1). With that model, Glashow proposed to unify electromagnetic and weak gauge interactions.