Low energy atmospheric muon neutrinos in MACRO

The MACRO Collaboration

doi:10.1016/S0370-2693(00)00267-7

paper

Low energy atmospheric muon neutrinos in MACRO

arXiv:hep-ex/0001044 · doi:10.1016/S0370-2693(00)00267-7

Abstract

We present the measurement of two event samples induced by atmospheric $ν_{μ}$ of average energy $E ˉ_{ν} \sim 4 G e V$ . In the first sample, the neutrino interacts inside the MACRO detector producing an upward-going muon leaving the apparatus. The ratio of the number of observed to expected events is $0.57 \pm 0.0 5_{s t a t} \pm 0.0 6_{sy s t} \pm 0.1 4_{t h eor}$ with an angular distribution similar to that expected from the Bartol atmospheric neutrino flux. The second is a mixed sample of internally produced downward-going muons and externally produced upward-going muons stopping inside the detector. These two subsamples are selected by topological criteria; the lack of timing information makes it impossible to distinguish stopping from downgoing muons. The ratio of the number of observed to expected events is $0.71 \pm 0.0 5_{s t a t} \pm 0.0 7_{sy s t} \pm 0.1 8_{t h eor}$ . Using the ratio of the two subsamples (for which most theoretical uncertainties cancel) we can test the pathlength dependence of the oscillation hypothesis. The probability of agreement with the no-oscillation hypothesis is 5% . The deviations of our observations from the expectations has a preferred interpretation in terms of $ν_{μ}$ oscillations with maximal mixing and $Δ m^{2} \sim 1 0^{- 3} \div 1 0^{- 2} e V^{2}$ . These parameters are in agreement with our results from upward throughgoing muons, induced by $ν_{μ}$ of much higher energies.

arXiv comment7 pages, 6 figures. Submitted to Phys. Lett. B

Low energy atmospheric muon neutrinos in MACRO

Abstract

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