We suggest that the reactions $\mathrm{pp}\to W^{\pm }\gamma X$ and $p\overline{p}\to W^{\pm }\gamma X$ are good candidates for measuring the magnetic moment parameter $\kappa$ in ${\mu }_W=\left(\frac{e}{2M_W}\right)(1+\kappa )$. The angular distribution of the $W$ bosons in $p\overline{p}\to W^{\pm }\gamma X$ is particularly sensitive to this parameter. For the gauge-theory value of $\kappa =1\mathrm{}$, we have found a peculiar zero in $\frac{d\sigma (d\overline{u}\to W^{-}\gamma )}{d}cos\theta$ at $cos\theta =-\frac{1}{3}$, the location of this zero depending on the quark charge through $cos\theta =-(1+2\mathrm{}{Q}_d)$. A similar zero occurs in $\frac{d\sigma (u\overline{d}\to W^{+}\gamma )}{d}cos\theta$. We can offer no explanation for this behavior.

• Received 5 June 1979

DOI:https://doi.org/10.1103/PhysRevLett.43.746