Low-energy photon production in neutrino neutral-current interactions

Abstract

The search for ${\nu }_{\mu }\to {\nu }_e$ oscillations by the MiniBooNE Collaboration at Fermilab has revealed a low-energy signal which could be due either to electrons produced by ${\nu }_e$ or photons produced by the interaction of the weak neutral current on the target nucleus. One contribution to the latter is a Wess-Zumino-Witten anomaly leading to a term in the Lagrangian proportional to ${ϵ}^{\mu \nu \kappa \lambda }{Z}_{\mu }{\omega }_{\nu }{F}_{\kappa \lambda }$. This term is normalized with the help of the known rates for the processes $f_1\to \rho \gamma$ and $\tau \to {\nu }_{\tau }{a}_1$. A rate of about 1/4 of that employed in several previous estimates is obtained. As the anomaly term had already been found to play a subdominant role in photon production (e.g., in comparison with $\Delta$ excitation and decay), the present estimate reduces its strength even further.

Comments: 8 pages, 1 figure. Version with significant further revisions submitted to Phys. Rev. D