The ratio of $\gamma / \pi^0$ production rates in neutrino-nucleus interactions at the $\Delta$ resonance mass region

Abstract

We study the dependence of neutrino-induced $\gamma/\pi^0$ production ($\stackrel{ {(-)}}{\nu_\mu} + A \to \stackrel{ {(-)}}{\nu_\mu}(\mu) +\gamma/\pi^0 + X$) on the target nucleus A, at the $\Delta$ resonance mass region. Our conclusion is based on experimental data for $\pi^0$ production rates at photon-nucleus interactions from the A2 collaboration at the Mainz MAMI accelerator. We assume that $\Delta$ resonance decays are independent of the production mechanism (via photon, Z, or W boson). In Neutral Current (NC) interactions, the $1\pi^0 + X$ production scales as A$^{2/3}$. In contrast, photons from $\Delta$ decays typically escape the nucleus, resulting in a cross-section proportional to the atomic number A. Thus, in NC interactions, the ratio of $\gamma$ production to $\pi^0$ production is proportional to A$^{1/3}$. In Charged Current (CC) $\nu_\mu$($\bar \nu_\mu$) -induced production of $\Delta^+$ ($\Delta^0$) will be proportional to the number of neutrons (protons) in the nucleus. After $\Delta$ decay, due to the charge universality in strong interactions, the suppression factor for $\pi^0$ escaping the nucleus must also follow A$^{-1/3}$, as in NC interactions. We predict the ratio of the $\gamma / \pi^0$ production rates in NC and CC interactions and for $\nu_\mu$ and $\bar \nu_\mu$ beams: {Argon target}: $\sim$3.1\% (NC/CC $\nu_\mu/\bar \nu_\mu$). {\bf Water target}: $\sim$1.9\% (NC), $\sim$2.3\% (CC $\nu_\mu$), $\sim$1.7\% (CC $\bar \nu_\mu$). {Liquid Scintillator target}: $\sim$1.7\% (NC), $\sim$2.1\% (CC $\nu_\mu$), $\sim$1.6\% (CC $\bar \nu_\mu$). We also discuss solving the MiniBooNE anomaly by looking at the CC single photon and single neutral pion production rates at the SBN program experiments at Fermilab.