[Paper Review] The MiniBooNE Experiment

A. A. Aguilar-Arevalo|arXiv (Cornell University)|Aug 16, 2004

Astrophysics and Cosmic Phenomena1 references3 citations

TL;DR

The MiniBooNE experiment was designed to definitively test the anomalous $¯{\nu}_\mu \to \u00af{\nu}_e$ oscillation signal reported by the LSND experiment. Using a neutrino beam from pion and kaon decays in a focused horn, the experiment employed a 12-meter-diameter mineral oil Cherenkov detector with 1280 photomultiplier tubes to detect neutrino interactions, aiming to confirm or refute LSND's 3.8σ signal with a sensitivity of 90% C.L. at 1×10²¹ protons on target.

ABSTRACT

MiniBooNE is an experiment designed to provide a definitive test for the numubar to nuebar oscillations signal seen by LSND. Here, a brief summary of the MiniBooNE goals and strategies is presented, as well as some highlights of its current status.

Motivation & Objective

• To definitively confirm or refute the LSND experiment's observation of $¯{\nu}_\mu \to \u00af{\nu}_e$ oscillations with a 3.8σ significance.
• To resolve the inconsistency between LSND's required $” m^2 \sim 0.3-3$ eV² and the three-neutrino Standard Model, which conflicts with solar and atmospheric neutrino oscillation data.
• To measure the $¯{\nu}_\mu \to \u00af{\nu}_e$ oscillation parameters with high precision using a high-statistics neutrino beam.
• To calibrate detector response using Michel electrons and cosmic ray muons for accurate energy and event reconstruction.
• To perform a blind analysis to prevent bias in the final oscillation signal search.

Proposed method

• A neutrino beam was produced by directing 8.0 GeV protons from Fermilab's Booster onto a beryllium target, with a focusing horn to enhance neutrino flux.
• The experiment operated in $¯{\nu}$ mode, increasing the neutrino flux at the detector by a factor of ~5 compared to uncollimated beams.
• The detector was a 12 m diameter sphere filled with mineral oil, instrumented with 1280 photomultiplier tubes (PMTs) to detect Cherenkov and scintillation light from neutrino interactions.
• An outer veto region with 240 PMTs and a tracking hodoscope above the detector identified cosmic ray backgrounds and measured muon trajectories.
• Laser calibration systems monitored PMT charge and time response continuously to maintain energy scale accuracy.
• The energy scale for electron-like events was calibrated using Michel electron spectra, and for muon-like events using cosmic ray muons.

Experimental results

Research questions

• RQ1 Does the LSND signal of $¯{\nu}_\mu \to \u00af{\nu}_e$ oscillations at $\Delta m^2 \sim 0.3-3$ eV² represent a real physical effect?
• RQ2 Can MiniBooNE distinguish between a true oscillation signal and background misidentification in the $\nu_\mu \to \nu_e$ channel?
• RQ3 What is the expected sensitivity of MiniBooNE to $\nu_\mu \to \nu_e$ oscillations at 1×10²¹ protons on target?
• RQ4 How accurately can the detector reconstruct neutrino energy and event topology for signal and background processes?
• RQ5 What are the dominant backgrounds to the $\nu_\mu \to \nu_e$ oscillation signal, and how can they be suppressed or modeled?

Key findings

• With 1×10²¹ protons on target, MiniBooNE expected approximately 300 signal events for LSND-like oscillations.
• The dominant background was misidentified $\nu_\mu$ interactions, primarily from neutral current $\pi^0$ production, contributing ~294 events.
• Intrinsic $\nu_e$ backgrounds were estimated at ~346 events, primarily from neutrino interactions in the beam and detector materials.
• The experiment achieved 90% confidence level sensitivity for $\nu_\mu \to \nu_e$ oscillations, with 3σ and 5σ sensitivity regions overlapping the LSND allowed region.
• The measurement capability for oscillation parameters was projected to reach 1σ and 2σ precision for both high and low $\Delta m^2$ regions at 1×10²¹ P.O.T.
• At the time of the paper, 30% of the target 1×10²¹ protons on target had been collected, and analysis of $\nu_\mu$ CCQE, NC $\pi^0$, and NC elastic scattering was ongoing.