A Standard Model explanation for the excess of electron-like events in MiniBooNE

Abstract

We study the dependence of neutral current (NC) neutrino-induced ${\pi }^0$/photon production (${\nu }_{\mu }+A\to {\nu }_{\mu }+1{\pi }^0/\gamma +X$) on the atomic number of the target nucleus, A, at 4-momentum transfers relevant to the MiniBooNE experiment: $\Delta$ resonance mass region. Our conclusion is based on experimental data for photon-nucleus interactions from the A2 collaboration at the Mainz MAMI accelerator. We work in the approximation that decays of $\Delta$ resonance unaffected by its production channel, via photon or Z boson. $1{\pi }^0+X$ production scales as A${}^{2/3}$, the surface area of the nucleus. Meanwhile the photons created in $\Delta$ decays will leave the nucleus, and that cross section will be proportional to the atomic number of the nucleus. Thus the ratio of photon production to ${\pi }^0$ production is proportional to A${}^{1/3}$. For carbon ${}^{12}$C this factor is $\approx$2.3. MiniBooNE normalises the rate of photon production to the measured ${\pi }^0$ production rate. The reduced neutral pion production rate would yield at least twice as many photons as previously expected, thus significantly lowering the number of unexplained electron-like events.

Comments: 2 pages, figure from A2 experiment added, minor changes in the text, reference added