Search for Sterile Neutrino Mixing in the MINOS Experiment

Search for Sterile Neutrino Mixing in the MINOS Experiment

Available online at www.sciencedirect.com Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 436 www.elsevier.com/locate/npbps Search for Sterile Neutr...

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Available online at www.sciencedirect.com

Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 436 www.elsevier.com/locate/npbps

Search for Sterile Neutrino Mixing in the MINOS Experiment P. Rodriguesa , A. Sousab , for the MINOS Collaboration a Subdepartment

of Particle Physics, University of Oxford, Oxford OX1 3RH, United Kingdom of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

b Department

Abstract In this poster, we present a search for disappearance of active neutrinos over a baseline of 735 km using the NuMI neutrino beam and the MINOS detectors. The data analyzed correspond to an exposure of 7.1×1020 protons-on-target. MINOS utilizes the most powerful neutrino beam currently in operation measured in two locations: a near detector at Fermilab, 1 km downstream of beam production, and a far detector, 734 km further away, in northern Minnesota. The poster characterizes the MINOS ability to measure neutral-current neutrino interactions, outlines the event selection methods employed and describes results obtained for three-flavour and four-flavour neutrino oscillation models.

0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.073

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MINOS Preliminary Far Detector Data

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θ13 = 0°

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The MINOS experiment is able to search for activesterile neutrino mixing by measuring the flux of neutralcurrent (NC) events at two locations separated by the atmospheric oscillation length. NC event rates are not affected by standard neutrino mixing, but the existence of one or more non-interacting neutrino species would induce an energy-dependent depletion measurable at the far site. The presented results are obtained using a data sample enlarged by more than a factor of two with respect to previous analyses [1, 2]. A total of 802 NC event candidates is observed in the far detector data whereas 757 ± 27.5(stat.) ± 37.3(syst.) events are expected from standard oscillations. The measured energy spectrum at the far detector is shown in Figure 1. Because charged-current νe -induced events are classified as NC with high efficiency by the analysis, the possibility of νe appearance at the maximal level allowed by the MINOS 90% confidence level (CL) limit for normal neutrino mass hierarchy is considered [3]. The mixing between active and sterile neutrinos is also quantifiable in terms of the fraction of disappearing νμ that may oscillate into non-interacting neutrino species ν s , given by the ratio of oscillation probabilities Pνμ →νs / (1−Pνμ →νμ ). We set a limit on this fraction, f s < 0.22 (0.40) at the 90% CL, where the number in parentheses is obtained

θ13 = 11.5°, δ = π

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νμ CC Background -3 |Δm232| = 2.35×10 eV2 2 sin 2θ23 = 1

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Figure 1: The reconstructed energy spectrum of NC-selected events at the far detector shown as points with statistical errors. The Monte Carlo prediction for standard three-flavor mixing is superimposed, both with (dashed line) and without (solid line) νe appearance at the new MINOS 90% CL limit.

if νe appearance is allowed. These results show no evidence for oscillations into sterile neutrinos in MINOS. [1] P. Adamson et al. (MINOS), Phys. Rev. Lett. 101 221804 (2008). [2] P. Adamson et al. (MINOS), Phys. Rev. D 81 052004 (2010). [3] P. Adamson et al. (MINOS), Phys. Rev. D 82 051102(R) (2010).