The PIENU experiment at TRIUMF is aimed at a measurement of the branching ratio $R^{e/mu}$ = ${Gammabig((pi^{+} rightarrow e^{+} u_{e}) + (pi^{+} rightarrow e^{+} u_{e}gamma)big)}/{Gammabig((pi^{+} rightarrow mu^{+} u_{mu})+(pi^{+} rightarrow mu^{
+} u_{mu}gamma)big)}$ with precision $<$0.1%. Incident pions, delivered at the rate of 60 kHz with momentum 75 MeV/c, were degraded and stopped in a plastic scintillator target. Pions and their decay product positrons were detected with plastic scintillators and tracked with multiwire proportional chambers and silicon strip detectors. The energies of the positrons were measured in a spectrometer consisting of a large NaI(T$ell$) crystal surrounded by an array of pure CsI crystals. This paper provides a description of the PIENU experimental apparatus and its performance in pursuit of $R^{e/mu}$.
This paper explores the use of $L/E$ oscillation probability distributions to compare experimental measurements and to evaluate oscillation models. In this case, $L$ is the distance of neutrino travel and $E$ is a measure of the interacting neutrinos
energy. While comparisons using allowed and excluded regions for oscillation model parameters are likely the only rigorous method for these comparisons, the $L/E$ distributions are shown to give qualitative information on the agreement of an experiments data with a simple two-neutrino oscillation model. In more detail, this paper also outlines how the $L/E$ distributions can be best calculated and used for model comparisons. Specifically, the paper presents the $L/E$ data points for the final MiniBooNE data samples and, in the Appendix, explains and corrects the mistaken analysis published by the ICARUS collaboration.
We report the measurement of the flux-averaged antineutrino neutral current elastic scattering cross section ($dsigma_{bar u N rightarrow bar u N}/dQ^{2}$) on CH$_{2}$ by the MiniBooNE experiment using the largest sample of antineutrino neutral cur
rent elastic candidate events ever collected. The ratio of the antineutrino to neutrino neutral current elastic scattering cross sections and a ratio of antineutrino neutral current elastic to antineutrino charged current quasi elastic cross section is also presented.
The MiniBooNE experiment at Fermilab reports results from an analysis of $bar u_e$ appearance data from $11.27 times 10^{20}$ protons on target in antineutrino mode, an increase of approximately a factor of two over the previously reported results.
An event excess of $78.4 pm 28.5$ events ($2.8 sigma$) is observed in the energy range $200<E_ u^{QE}<1250$ MeV. If interpreted in a two-neutrino oscillation model, $bar{ u}_{mu}rightarrowbar{ u}_e$, the best oscillation fit to the excess has a probability of 66% while the background-only fit has a $chi^2$-probability of 0.5% relative to the best fit. The data are consistent with antineutrino oscillations in the $0.01 < Delta m^2 < 1.0$ eV$^2$ range and have some overlap with the evidence for antineutrino oscillations from the Liquid Scintillator Neutrino Detector (LSND). All of the major backgrounds are constrained by in-situ event measurements so non-oscillation explanations would need to invoke new anomalous background processes. The neutrino mode running also shows an excess at low energy of $162.0 pm 47.8$ events ($3.4 sigma$) but the energy distribution of the excess is marginally compatible with a simple two neutrino oscillation formalism. Expanded models with several sterile neutrinos can reduce the incompatibility by allowing for CP violating effects between neutrino and antineutrino oscillations.
The largest sample ever recorded of $ umub$ charged-current quasi-elastic (CCQE, $ umub + p to mup + n$) candidate events is used to produce the minimally model-dependent, flux-integrated double-differential cross section $frac{d^{2}sigma}{dT_mu duz}
$ for $ umub$ incident on mineral oil. This measurement exploits the unprecedented statistics of the MiniBooNE anti-neutrino mode sample and provides the most complete information of this process to date. Also given to facilitate historical comparisons are the flux-unfolded total cross section $sigma(E_ u)$ and single-differential cross section $frac{dsigma}{dqsq}$ on both mineral oil and on carbon by subtracting the $ umub$ CCQE events on hydrogen. The observed cross section is somewhat higher than the predicted cross section from a model assuming independently-acting nucleons in carbon with canonical form factor values. The shape of the data are also discrepant with this model. These results have implications for intra-nuclear processes and can help constrain signal and background processes for future neutrino oscillation measurements.
A proposal submitted to the FNAL PAC is described to search for light sub-GeV WIMP dark matter at MiniBooNE. The possibility to steer the beam past the target and into an absorber leads to a significant reduction in neutrino background, allowing for
a sensitive search for elastic scattering of WIMPs off nucleons or electrons in the detector. Dark matter models involving a vector mediator can be probed in a parameter region consistent with the required thermal relic density, and which overlaps the region in which these models can resolve the muon g-2 discrepancy. Estimates of signal significance are presented for various operational modes and parameter points. The experimental approach outlined for applying MiniBooNE to a light WIMP search may also be applicable to other neutrino facilities.
We propose adding 300 mg/l PPO to the existing MiniBooNE detector mineral oil to increase the scintillation response. This will allow the detection of associated neutrons and increase sensitivity to final-state nucleons in neutrino interactions. This
increased capability will enable an independent test of whether the current excess seen in the MiniBooNE oscillation search is signal or background. In addition it will enable other neutrino interaction measurements to be made including a search for the strange-quark contribution to the nucleon spin Delta s and a low-energy measurement of charged-current quasielastic scattering.
The MiniBooNE experiment at Fermilab reports results from an analysis of the combined $ u_e$ and $bar u_e$ appearance data from $6.46 times 10^{20}$ protons on target in neutrino mode and $11.27 times 10^{20}$ protons on target in antineutrino mode.
A total excess of $240.3 pm 34.5 pm 52.6$ events ($3.8 sigma$) is observed from combining the two data sets in the energy range $200<E_ u^{QE}<1250$ MeV. In a combined fit for CP-conserving $ u_mu rightarrow u_e$ and $bar{ u}_{mu}rightarrowbar{ u}_e$ oscillations via a two-neutrino model, the background-only fit has a $chi^2$-probability of 0.03% relative to the best oscillation fit. The data are consistent with neutrino oscillations in the $0.01 < Delta m^2 < 1.0$ eV$^2$ range and with the evidence for antineutrino oscillations from the Liquid Scintillator Neutrino Detector (LSND).
The sidereal time dependence of MiniBooNE electron neutrino and anti-electron neutrino appearance data are analyzed to search for evidence of Lorentz and CPT violation. An unbinned Kolmogorov-Smirnov test shows both the electron neutrino and anti-ele
ctron neutrino appearance data are compatible with the null sidereal variation hypothesis to more than 5%. Using an unbinned likelihood fit with a Lorentz-violating oscillation model derived from the Standard Model Extension (SME) to describe any excess events over background, we find that the electron neutrino appearance data prefer a sidereal time-independent solution, and the anti-electron neutrino appearance data slightly prefer a sidereal time-dependent solution. Limits of order 10E-20 GeV are placed on combinations of SME coefficients. These limits give the best limits on certain SME coefficients for muon neutrino to electron neutrino and anti-muon neutrino to anti-electron neutrino oscillations. The fit values and limits of combinations of SME coefficients are provided.
Two independent methods are employed to measure the neutrino flux of the anti-neutrino-mode beam observed by the MiniBooNE detector. The first method compares data to simulated event rates in a high purity $ umu$ induced charged-current single $pip$
(CC1$pip$) sample while the second exploits the difference between the angular distributions of muons created in $ umu$ and $ umub$ charged-current quasi-elastic (CCQE) interactions. The results from both analyses indicate the prediction of the neutrino flux component of the pre-dominately anti-neutrino beam is over-estimated - the CC1$pip$ analysis indicates the predicted $ umu$ flux should be scaled by $0.76 pm 0.11$, while the CCQE angular fit yields $0.65 pm 0.23$. The energy spectrum of the flux prediction is checked by repeating the analyses in bins of reconstructed neutrino energy, and the results show that the spectral shape is well modeled. These analyses are a demonstration of techniques for measuring the neutrino contamination of anti-neutrino beams observed by future non-magnetized detectors.
