# A Letter of Intent to Build a MiniBooNE Near Detector: BooNE

## TL;DR

This paper proposes building a second MiniBooNE detector at a shorter distance to test neutrino oscillation anomalies, differences between neutrino and antineutrino behaviors, and potential CP/CPT violation at short baselines.

## Contribution

It introduces a plan to construct a second detector to enable precise oscillation measurements and comparisons between neutrino and antineutrino modes, addressing current anomalies and potential violations.

## Key findings

- No excess of electron-like events in antineutrino mode so far
- Potential difference between neutrino and antineutrino oscillations suggested by global fits
- Method proposed for sensitive tests of oscillations and CP/CPT violation

## Abstract

There is accumulating evidence for a difference between neutrino and antineutrino oscillations at the $\sim 1$ eV$^2$ scale. The MiniBooNE experiment observes an unexplained excess of electron-like events at low energies in neutrino mode, which may be due, for example, to either a neutral current radiative interaction, sterile neutrino decay, or to neutrino oscillations involving sterile neutrinos and which may be related to the LSND signal. No excess of electron-like events ($-0.5 \pm 7.8 \pm 8.7$), however, is observed so far at low energies in antineutrino mode. Furthermore, global 3+1 and 3+2 sterile neutrino fits to the world neutrino and antineutrino data suggest a difference between neutrinos and antineutrinos with significant ($\sin^22\theta_{\mu \mu} \sim 35%$) $\bar \nu_\mu$ disappearance. In order to test whether the low-energy excess is due to neutrino oscillations and whether there is a difference between $\nu_\mu$ and $\bar \nu_\mu$ disappearance, we propose building a second MiniBooNE detector at (or moving the existing MiniBooNE detector to) a distance of $\sim 200$ m from the Booster Neutrino Beam (BNB) production target. With identical detectors at different distances, most of the systematic errors will cancel when taking a ratio of events in the two detectors, as the neutrino flux varies as $1/r^2$ to a calculable approximation. This will allow sensitive tests of oscillations for both $\nu_e$ and $\bar \nu_e$ appearance and $\nu_\mu$ and $\bar \nu_\mu$ disappearance. Furthermore, a comparison between oscillations in neutrino mode and antineutrino mode will allow a sensitive search for CP and CPT violation in the lepton sector at short baseline ($\Delta m^2 > 0.1$ eV$^2$).