Search for Neutrino-Induced Neutral Current $\Delta$ Radiative Decay in MicroBooNE and a First Test of the MiniBooNE Low Energy Excess Under a Single-Photon Hypothesis

The collaboration
Phys.Rev.Lett. 128 (2022) 111801, 2022.

Abstract (data abstract)
We report results from a search for neutrino-induced neutral current (NC) resonant $\Delta$(1232) baryon production followed by $\Delta$ radiative decay, with a ⟨0.8⟩ GeV neutrino beam. Data corresponding to MicroBooNE’s first three years of operations (6.80×$10^{20}$ protons on target) are used to select single-photon events with one or zero protons and without charged leptons in the final state ($1\gamma1p$ and $1\gamma0p$, respectively). The background is constrained via an in-situ high-purity measurement of NC $\pi^{0}$ events, made possible via dedicated $2\gamma1p$ and $2\gamma0p$ selections. A total of 16 and 153 events are observed for the $1\gamma1p$ and $1\gamma0p$ selections, respectively, compared to a constrained background prediction of 20.5 ± 3.65(sys.) and 145.1 ± 13.8(sys.) events. The data lead to a bound on an anomalous enhancement of the normalization of NC $\Delta$ radiative decay of less than 2.3 times the predicted nominal rate for this process at the 90% confidence level (CL). The measurement disfavors a candidate photon interpretation of the MiniBooNE low-energy excess as a factor of 3.18 times the nominal NC $\Delta$ radiative decay rate at the 94.8% CL, in favor of the nominal prediction, and represents a greater than 50-fold improvement over the world’s best limit on single-photon production in NC interactions in the sub-GeV neutrino energy range.

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Data and MC comparison of the reconstructed $\pi^0$ momentum distribution for the 2$\gamma$1p selected events

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Figure 1(a) on page 4

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Data/MC ratio as a function of reconstructed $\pi^0$ momentum for the 2$\gamma$1p selection

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Figure 1(b) on page 4

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Data and MC comparison of the reconstructed $\pi^0$ momentum distribution for the 2$\gamma$0p selected events

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Figure 1(b) on page 4

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Data/MC ratio as a function of reconstructed $\pi^0$ momentum for the 2$\gamma$0p selection

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Figure 2(a) on page 6

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Energy spectra for the 1$\gamma$1p selected events. The figure shows the unconstrained background prediction and breakdowns as a function of...

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Figure 2(a) on page 6

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Energy spectra for the 1$\gamma$1p selected events. This figure shows the total background prediction with systematic uncertainty both before and...

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Figure 2(b) on page 6

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Energy spectra for the 1$\gamma$0p selected events. The figure shows the unconstrained background prediction and breakdowns as a function of...

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Figure 2(b) on page 6

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Energy spectra for the 1$\gamma$0p selected events. This figure shows the total background prediction with systematic uncertainty both before and...

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Figure 3(a) on page 6

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The observed event rate for the 1$\gamma$1p event sample, and comparisons to unconstrained (left) and constrained (right) background and LEE...

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Figure 3(b) on page 6

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The observed event rate for the 1$\gamma$0p event sample, and comparisons to unconstrained (left) and constrained (right) background and LEE...

• #### Supplementary material, Table III

On supplementary material page 4, Table III in Sec. III

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The fractional systematic covariance matrix for the final selected 1$\gamma$1p, 1$\gamma$0p, 2$\gamma$1p, and 2$\gamma$0p event samples, in bins of reconstructed...

• #### Supplementary material, TABLE IV

On supplementary material page 5, TABLE IV in Sec. III

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The fractional systematic covariance matrix for the final selected 1$\gamma$1p, 1$\gamma$0p, 2$\gamma$1p, and 2$\gamma$0p event samples, in bins of reconstructed...