L. Corwin: MINOS Results
I will not discuss the detailed description of the detectors (near and far) that was provided by the speaker in this talk. Let me just briefly discuss what was shown, as far as the results are concerned.
MINOS achieved 1.7×10^20 protons on target in the antineutrino mode, and 7×10^20 in the neutrino mode. These data produce quite precise measurements of the muon neutrino oscillation parameters through their disappearance.
Oscillation of muon neutrinos to other flavours will manifest as a deficit at the far detector. Charged current interactions can be distinguished very well, using a well-tested paradigm (a hadronic shower with a long track from the generated muon).
The new result of MINOS has been in the arxiv since a week ago. They have the World’s most precise delta_m^2 measurement: 2.32+0.12-0.08 x10^-3 eV^2.
Antineutrinos also undergo CC interactions yielding positive muons. The antineutrino beam is not 93% pure as the neutrino beam: it is only 40% pure. So they need to select events with positive reconstructed muon charge. Uncertainties are dominated by statistics.
According to the slides, “systematics were incorporated in the result with the Feldman-Cousins method” – this does not make sense to me, since FC is a unified method for constructing a confidence belt, while the way systematics are included in a measurement is a different topic altogether; maybe he got confused with the “Cousins-Highland” method of incorporating systematics in an upper limit by quasi-frequentist integration of the nuisance parameters…
Anyway, let us get back to the talk. What does MINOS find in their oscillation analysis from comparing neutrinos and antineutrinos ? Well, it appears that there is presently an interesting tension between neutrinos and antinenutrins, at the 2.3 sigma difference, in the oscillation parameters. Definitely something to watch closely in the future!
One bonus track after the main result: the far detector of Minos can also detect atmospheric neutrinos. The baseline is from 10 to 13000 km, and the L/E parameter spans 4 orders of magnitude. The data is divided in events with neutrino interactions in the detector and events in the rock producing upward going muons. A likelihood fit to the L/E distribution produces the oscillation parameters. The fit results have lower accuracy than the beam results, but they are still consistent.
In the future, new antineutrino analysis with an at least doubled dataset is predicted. New electron neutrino results will also be produced, as well as an improved atmospheric neutrino result.