Enhanced search for neutral current $Δ$ radiative single-photon production in MicroBooNE

Abstract

We report results from an updated search for neutral current (NC) resonant $Δ$(1232) baryon production and subsequent $Δ$ radiative decay (NC $Δ\rightarrow N γ$). We consider events with and without final state protons; events with a proton can be compared with the kinematics of a $Δ(1232)$ baryon decay, while events without a visible proton represent a more generic phase space. In order to maximize sensitivity to each topology, we simultaneously make use of two different reconstruction paradigms, Pandora and Wire-Cell, which have complementary strengths, and select mostly orthogonal sets of events. Considering an overall scaling of the NC $Δ\rightarrow N γ$ rate as an explanation of the MiniBooNE anomaly, our data exclude this hypothesis at 94.4% CL. When we decouple the expected correlations between NC $Δ\rightarrow N γ$ events with and without final state protons, and allow independent scaling of both types of events, our data exclude explanations in which excess events have associated protons, and do not exclude explanations in which excess events have no associated protons.

Figures (5)

• Figure 1: Wire-Cell and Pandora signal channels, unconstrained and constrained. The no-NC $\Delta\rightarrow N \gamma$ prediction is shown in black, with diagonal hashes indicating the systematic uncertainty. The LEE prediction with a $x_\Delta=3.18$ enhancement of the nominal NC $\Delta\rightarrow N \gamma$ is shown in green and orange for signal with and without true final state protons with kinetic energy of at least 35 MeV, respectively. The Pandora and Wire-Cell samples correspond to $6.80\times 10^{20}$ and $6.37\times 10^{20}$ POT, respectively.
• Figure 2: Wire-Cell and Pandora signal channel shower energy distributions, constrained by sideband observations. The prediction shows the nominal NC $\Delta\rightarrow N \gamma$ scaling, $x_\Delta=1$. The top panels have bin widths of 100 MeV, while the bottom panels have bin widths of 50 MeV. In each panel, the rightmost bin is an overflow bin. The Pandora and Wire-Cell samples correspond to $6.80\times 10^{20}$ and $6.37\times 10^{20}$ POT, respectively.
• Figure 3: NC $\Delta\rightarrow N \gamma$ scaling exclusions. Black horizontal dashed lines indicate 68% and 90% CL values. The effective branching fraction and cross section are simple rescalings of the $x_\Delta$ scale factor. The Pandora and Wire-Cell samples correspond to $6.80\times 10^{20}$ and $6.37\times 10^{20}$ POT, respectively.
• Figure 4: Two-dimensional $x_{\Delta Np}$ and $x_{\Delta 0p}$ scaling exclusion sensitivity with Asimov data, a fake data set that exactly matches the prediction. One-dimensional profiles are shown in the top and right, with a dashed line indicating 90% CL. The hashed region indicates the side of each curve which is being excluded. The Pandora and Wire-Cell Asimov data samples correspond to $6.80\times 10^{20}$ and $6.37\times 10^{20}$ POT, respectively.
• Figure 5: Two-dimensional $x_{Np}$ and $x_{0p}$ scaling data exclusions. One-dimensional profiles are shown in the top and right, with a dashed line indicating 90% CL. The hashed region indicates the side of each curve which is being excluded. The Pandora and Wire-Cell data samples correspond to $6.80\times 10^{20}$ and $6.37\times 10^{20}$ POT, respectively.