[Paper Review] Latest Results from the MiniBooNE Experiment and Updated Oscillation Sensitivity

J. Monroe|ArXiv.org|Jun 17, 2004

Neutrino Physics Research9 references3 citations

TL;DR

This paper presents preliminary results from the MiniBooNE experiment, which aims to confirm or refute the anomalous $ ue$ appearance signal reported by the LSND experiment. Using $1\times10^{21}$ protons on target, the experiment measures $ ue$-like events via charged-current quasi-elastic scattering, neutral-current $ pi^0$ production, and neutral-current elastic scattering, achieving a sensitivity to $ mu\to ue$ oscillations that covers the LSND allowed region at 90% C.L. The updated oscillation sensitivity indicates MiniBooNE can definitively test the LSND signal within its planned data set.

ABSTRACT

Neutrino oscillations have been established in solar and atmospheric neutrinos, but a third signal from the LSND experiment is incompatible with three Standard Model neutrinos. The MiniBooNE experiment can confirm or refute the LSND oscillation signal with 1E21 protons on target. Preliminary results on muon neutrino analyses and an updated oscillation sensitivity are presented.

Motivation & Objective

• To definitively test the LSND experiment's claim of $ mu\to ue$ oscillations with a $3.8\sigma$ excess at short baselines.
• To resolve the incompatibility between LSND's $\Delta m^2 \sim 0.3-3\ \mathrm{eV}^2$ signal and the three-neutrino Standard Model framework.
• To measure $ mu\to ue$ oscillation parameters with improved statistics and reduced systematic errors compared to LSND.
• To determine whether the LSND signal is due to new physics, such as sterile neutrinos, by testing the oscillation hypothesis with a high-precision, high-statistics experiment.

Proposed method

• The MiniBooNE experiment uses a 8.89 GeV/c proton beam incident on a beryllium target to produce a $ mu$-dominated neutrino beam via meson decays in a 50 m decay pipe.
• Neutrino detection occurs in a 6.1 m radius spherical detector filled with mineral oil, instrumented with 1280 inward-facing and 240 outward-facing photomultiplier tubes for particle identification.
• Event selection relies on beam spill timing, low veto PMT hits (<6), and high tank PMT hits (>200), achieving >999:1000 cosmic ray background rejection.
• Signal identification uses prompt Cherenkov light and delayed scintillation from charged particles, with calibration via laser systems, stopping muons, Michel electrons, and $ pi^0$ decays.
• Backgrounds from $ ue$ in the beam and misidentified $ mu$-induced events are modeled and subtracted using beam-on and beam-off data, with systematic errors estimated at 5–10%.
• Oscillation sensitivity is computed via Monte Carlo simulations tuned to calibration data, with event rate predictions normalized to protons on target.

Experimental results

Research questions

• RQ1 Can MiniBooNE confirm or rule out the LSND signal of $ mu\to ue$ oscillations at the $3.8\sigma$ level with higher statistics and better systematics?
• RQ2 What is the sensitivity of MiniBooNE to the $ mu\to ue$ oscillation parameters in the $\Delta m^2 \sim 0.3-3\ \mathrm{eV}^2$ range?
• RQ3 How well can MiniBooNE distinguish between true $ ue$ appearance and backgrounds from intrinsic $ ue$ in the beam or misidentified $ mu$ events?
• RQ4 What is the expected measurement capability for $\sin^2 2\theta$ and $\Delta m^2$ in the event of a positive signal at high or low $\Delta m^2$?
• RQ5 To what extent do neutral-current $ pi^0$ and elastic scattering events constrain the optical model and background rejection in the detector?

Key findings

• The MiniBooNE experiment has collected approximately 20% of the planned $1\times10^{21}$ protons on target by the time of this report.
• The signal-like neutral current $ pi^0$ yield is measured at $2425 \pm 107$ events after background subtraction, with good agreement between data and Monte Carlo in $p_{\pi^0}$, energy asymmetry, and $\cos\theta_{\pi^0}$ distributions.
• The neutral current elastic scattering sample contains approximately 25,000 events, with a reconstruction efficiency of 60% and purity of 81%.
• The updated $ mu\to ue$ oscillation sensitivity at $1\times10^{21}$ protons on target covers the LSND allowed region at 90% confidence level.
• The sensitivity reaches 3$\sigma$ and 5$\sigma$ coverage of the LSND signal region, indicating high potential to confirm or exclude the anomaly.
• The parameter measurement capability for $\Delta m^2$ and $\sin^2 2\theta$ is quantified in the event of a positive signal, with 1$\sigma$ and 2$\sigma$ contours shown for high and low $\Delta m^2$ regions.