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J. Coelho: Status of MINOS and MINOS+

March 5, 2015

The NuMi beam at Fermilab is running at 350kW but is capable of twice as much power. Minos took data at low energy earlier but 1.5 years ago it was changed so Minos is now seeing a broader energy spectrum.

Minos has a near detector at FNAL and a far one at 735km in the Soudan mine in Minnesota (see Fig.1). The NuMI beam has produced over 2×10^21 protons on target. Since the change of beam energy they produced 4.6×10^20 pot. The intensity will be ramped up soon to 400kW.

minos1

The near detector is 1kT, the far one 5.4kT. it is a magnetized steel-scintillator tracking calorimeter. It detects both charged-current muon interactions, electron showers, and neutral-current events where only a hadron shower is seen.

The goal of detecting muon neutrino disappearance, electron neutrino appearance, neutral currents to infer tau neutrinos. Maybe tau neutrino appearance can be also tried in Minos+, but it has high backgrounds. Figure 2 below shows the three main processes Minos is sensitive to, and the typical topologies reconstructable in the detector that correspond to them.

minos2

The results obtained so far, by combining all neutrino data, bring in the best measurement of delta_m^2(32), at 3.8% precision. What they are really interested now are however exotic phenomena, like sterile neutrinos. They are looking at a model with one extra state, with some mixing with the other three eigenstates. This would produce a distortion in the far detector, with a high-energy tail in the spectrum, if delta_m^2(43) were smaller than 0.5 eV^2; otherwise distortions would be observable at the near detector, but smeared by the parent decay position due to the sensitivity to the baseline of the effect.

minos3So far, the ratios of far and near detector yields and spectra are consistent with no active-to-sterile neutrino mixing, which indicates that the muon neutrinos must be actually transforming into tau neutrinos (a sketch of the mass splitting of the neutrino states, in presence of a sterile neutrino, is shown on the right in Fig.3). Contours and excluded regions in the parameter space are produced, which exclude a large previously unexplored region at low delta_m^2(43) and large sin^2(2theta_24) (see Figure 4, below). By combining with Bugey data excluding most of the region of parameter space allowed by LSND and MiniBooNE.

Another model they looked into is Lorentz and CPT violation. This can lead to neutrino to antineutrino transitions. No excess at low muon antineutrino energy is observed, and constraints are set on the model.

minos4Extra interactions of neutrinos in matter might lead to an alteration of the oscillation pattern. The muon neutrino disappearance is most sensitive to muon-tau coupling; this can be studied by comparing muon neutrino and antineutrino data. No evidence for non-standard interaction is seen in Minos data.

With Minos+, at higher energy there is improved sensitivity to new physics such as that cited above. The preliminary data show no strange effects. For sterile neutrinos they ay improve the exclusion at very low delta_m values.

Electron neutrino appearance due to sterile neutrino mixing can be studied with Minos+. The sensitivity is similar to that of ICARUS.

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