UCL Discovery

Abstract

The MINOS experiment is a long-baseline neutrino oscillation experiment which sends a high intensity muon neutrino beam through two functionally identical detectors, a Near detector at the Fermi National Accelerator Laboratory in Illinois, 1km from the beam source, and a Far detector, 734km away, in the Soudan Mine in Minnesota. MINOS may be able to measure the neutrino mixing angle parameter sin{^2}2\theta{_1_3} for the first time. Detector granularity, however, makes it very hard to distinguish any \nu{_e} appearance signal events characteristic of a non-zero value of \theta{_1_3} from background neutral current (NC) and short-track \nu{_\mu} charged current (CC) events. Also, uncertainties in the hadronic shower modeling in the kinematic region characteristic of this analysis are relatively large. A new data-driven background decomposition method designed to address those issues is developed and its results presented. By removing the long muon tracks from \nu{_\mu}-CC events, the Muon Removed Charge Current (MRCC) method creates independent pseudo-NC samples that can be used to correct the MINOS Monte Carlo to agree with the high-statistics Near detector data and to decompose the latter into components so as to predict the expected Far detector background. The MRCC method also provides an important cross-check in the Far detector to test the background in the signal selected region. MINOS finds a 1.0-1.5 \sigma\nu{_e}-CC excess above background in the Far detector data, depending on method used, for a total exposure of 3.14x10{^20} protons-on-target. Interpreting this excess as signal, MINOS can set limits on sin{^2}2\theta{_1_3}. Using the MRCC method, MINOS sets a limit of sin{^2}2\theta{_1_3} < 0:265 at the 90% confidence limit for a CP-violating phase \delta = 0.

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