Measurement of the off-axis NuMI Neutrinos

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Aithousa Mitropoulos ()

Aithousa Mitropoulos

Megaron, Athens - Greece


Dr Zelimir Djurcic (Argonne National Laboratory)


\documentclass[11pt]{article} \hoffset -.68in \voffset -1.0in \textwidth 6.5in \textheight 9.2in \begin{document} \begin{center}{\bf Measurement of the off-axis NuMI Neutrinos}\\ Zelimir Djurcic\\ {\it Argonne National Laboratory, Argonne, IL 60439, USA}\\ \end{center} \normalsize Fermi National Accelerator Laboratory has two beam lines that produce neutrinos: the Booster Neutrino Beam (BNB) and the NuMI beam line. The BNB beam is designed for use by the MiniBooNE experiment. Motivated by the LSND observation of an excess of observed $\bar{\nu}_e$ events above Monte Carlo prediction in a $\bar{\nu}_{\mu}$ beam, the MiniBooNE experiment was designed to test the neutrino oscillation interpretation of the LSND signal in both neutrino and anti-neutrino modes. The MiniBooNE collaboration has performed a search for $\nu_\mu \rightarrow \nu_e$ oscillations with $6.486 \times 10^{20}$ protons on target (POT), the results of which showed no evidence of an excess of $\nu_e$ events for neutrino energies above 475 MeV. Despite having observed no evidence for oscillations above 475 MeV, the MiniBooNE $\nu_{\mu}\rightarrow\nu_e$ search observed a sizable excess (128.8$\pm$43.4 events) at low energy, between 200-475 MeV. Although the excess is incompatible with LSND-type oscillations, several hypotheses, including sterile neutrino oscillations with CP violation, anomaly-mediated neutrino-photon coupling, and many others, have been proposed that provide a possible explanation for the excess itself. In some cases, these theories offer the possibility of reconciling the MiniBooNE $\nu_e$ excess with the LSND $\bar{\nu}_e$ excess. The MiniBooNE collaboration also reported initial results from a search for $\bar{\nu}_{\mu}\rightarrow\bar{\nu}_e$ oscillations, using a data sample corresponding to $3.386 \times 10^{20}$ POT. No significant excess of events has been observed, both at low energy, 200-475 MeV, and at high energy, 475-1250 MeV, although the data are inconclusive with respect to antineutrino oscillations at the LSND level. MiniBooNE will be showing additional anti-neutrino data in this conference.\\ The NuMI beam produces neutrinos for the MINOS experiment and it will be supplying the NO$\nu$A experiment with neutrinos. The MiniBooNE detector observes neutrinos from the NuMI beamline, at an off-axis angle of 6.3 degrees. Samples of charged current quasi-elastic (CCQE) $\nu_{\mu}$ and $\nu_e$ interactions were analyzed. The high rate and simple topology of $\nu_{\mu}$ CCQE events provided a useful sample for understanding the $\nu_{\mu}$ spectrum and verifying the MC prediction for $\nu_{e}$ production. The first result of the analysis is published in P.~Adamson {\it et al.}, Phys. Rev. Lett. {\bf 102}, 211801 (2009), arXiv:0809.2447 [hep-ex] and show that reliable predictions for an off-axis beam can be made. After the demonstration of the off-axis concept, useful in limiting backgrounds in searches for the oscillation transition $\nu_{\mu} \rightarrow \nu_e$, the analysis is directed toward examing the low energy region and searching for oscillation. In this way it complements the analysis done at MiniBooNE using the BNB neutrino and anti-neutrino BNB, but with different systematics. The current off-axis accelerator based long baseline experiments, in particular the NOvA, would benefit from understanding and careful calibration of the off-axis beam components that may be extrapolated to NOvA off-axis position as the NOVA will use same NuMI beam and will be plastic liquid scintillation detector similar to MiniBooNE.\\ The analysis is being performed by forming a correlation between the large statistics $\nu_{\mu}$ CCQE sample and $\nu_{e}$ CCQE, and by tuning the prediction to the data simultaneously. Considering various sources of systematic uncertainty, a covariance matrix in bins of $E_{\nu}$ is constructed, which includes correlations between $\nu_e$ CCQE (oscillation signal and background) and $\nu_{\mu}$ CCQE samples. This covariance matrix is used in the $\chi^2$ calculation of the oscillation fit. The result is that the prediction is being constrained, i.e. tuned to the data, and common systematic components in $\nu_e$ and $\nu_{\mu}$ CCQE samples cancel. The cancellation results from the fact that the majority of the events in both $\nu_e$ and $\nu_{\mu}$ CCQE samples originate from pure charged current interaction of neutrinos sharing same parent mesons, effectively sharing same cross-section and beam systematic components. This is a method equivalent to forming a ratio between near and far detectors in two-detector experiments where the near detector detects $\nu_{\mu}$ CCQE events, while the far detector samples $\nu_{e}$ CCQE events. Progress in the analysis and any available results will be discussed. \end{document}

Primary author

Dr Zelimir Djurcic (Argonne National Laboratory)

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