Person:

Feldman, Gary

A review of accelerator long-baseline neutrino oscillation experiments is provided, including all experiments performed to date and the projected sensitivity of those currently in progress. Accelerator experiments have played a crucial role in the confirmation of the neutrino oscillation phenomenon and in precision measurements of the parameters. With a fixed baseline and detectors providing good energy resolution, precise measurements of the ratio of distance/energy (L/E) on the scale of individual events have been made and the expected oscillatory pattern resolved. Evidence for electron neutrino appearance has recently been obtained, opening a door for determining the CP violating phase as well as resolving the mass hierarchy and the octant of theta23: some of the last unknown parameters of the standard model extended to include neutrino mass.

Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of 7.07×10207.07×1020 protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of 754±28(stat.)±37(syst.)754±28(stat.)±37(syst.) for oscillations among three active flavors. The fraction fsfs of disappearing \numu that may transition to νsνs is found to be less than 22% at the 90% C.L.

We searched for a sidereal modulation in the MINOS far detector neutrino rate. Such a signal would be a consequence of Lorentz and CPT violation as described by the standard-model extension framework. It also would be the first detection of a perturbative effect to conventional neutrino mass oscillations. We found no evidence for this sidereal signature, and the upper limits placed on the magnitudes of the Lorentz and CPT violating coefficients describing the theory are an improvement by factors of 20–510 over the current best limits found by using the MINOS near detector.

The energy dependence of the neutrino-iron and antineutrino-iron inclusive charged-current cross sections and their ratio have been measured using a high-statistics sample with the MINOS near detector exposed to the NuMI beam from the main injector at Fermilab. Neutrino and antineutrino fluxes were determined using a low hadronic energy subsample of charged-current events. We report measurements of ν−Fe (ν⎯⎯−Fe) cross section in the energy range 3–50 GeV (5–50 GeV) with precision of 2%–8% (3%–9%) and their ratio which is measured with precision 2%–8%. The data set spans the region from low energy, where accurate measurements are sparse, up to the high-energy scaling region where the cross section is well understood.

A sample of 1.53×109 cosmic-ray-induced single muon events has been recorded at 225 m water equivalent using the MINOS near detector. The underground muon rate is observed to be highly correlated with the effective atmospheric temperature. The coefficient αT, relating the change in the muon rate to the change in the vertical effective temperature, is determined to be 0.428±0.003(stat.)±0.059(syst.). An alternative description is provided by the weighted effective temperature, introduced to account for the differences in the temperature profile and muon flux as a function of zenith angle. Using the latter estimation of temperature, the coefficient is determined to be 0.352±0.003(stat.)±0.046(syst.).

We report measurements of oscillation parameters from νμ and ν⎯⎯μ disappearance using beam and atmospheric data from MINOS. The data comprise exposures of 10.71×1020 protons on target in the νμ-dominated beam, 3.36×1020 protons on target in the ν⎯⎯μ-enhanced beam, and 37.88 kton yr of atmospheric neutrinos. Assuming identical ν and ν⎯⎯ oscillation parameters, we measure |Δm2|=(2.41+0.09−0.10)×10−3  eV2 and sin2(2θ)=0.950+0.035−0.036. Allowing independent ν and ν⎯⎯ oscillations, we measure antineutrino parameters of |Δm⎯⎯⎯2|=(2.50+0.23−0.25)×10−3  eV2 and sin2(2θ⎯⎯)=0.97+0.03−0.08, with minimal change to the neutrino parameters.

The CoGeNT Collaboration has recently published results from a fifteen month data set which indicate an annual modulation in the event rate similar to what is expected from weakly interacting massive particle interactions. It has been suggested that the CoGeNT modulation may actually be caused by other annually modulating phenomena, specifically the flux of atmospheric muons underground or the radon level in the laboratory. We have compared the phase of the CoGeNT data modulation to that of the concurrent atmospheric muon and radon data collected by the MINOS experiment which occupies an adjacent experimental hall in the Soudan Underground Laboratory. The results presented are obtained by performing a shape-free χ2 data-to-data comparison and from a simultaneous fit of the MINOS and CoGeNT data to phase-shifted sinusoidal functions. Both tests indicate that the phase of the CoGeNT modulation is inconsistent with the phases of the MINOS muon and radon modulations at the 3.0σ level.

Measurements of neutrino oscillations using the disappearance of muon neutrinos from the Fermilab NuMI neutrino beam as observed by the two MINOS detectors are reported. New analysis methods have been applied to an enlarged data sample from an exposure of 7.25×10207.25×1020 protons on target. A fit to neutrino oscillations yields values of |Δm2|=(2.32+0.12−0.08)×10−3|Δm2|=(2.32−0.08+0.12)×10−3,eV22 for the atmospheric mass splitting and sin2(2θ)>0.90sin2(2θ)>0.90 (90%,C.L.) for the mixing angle. Pure neutrino decay and quantum decoherence hypotheses are excluded at 7 and 9 standard deviations, respectively.

We report the results of a search for νe appearance in a νμ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of 8.2×1020 protons on the NuMI target at Fermilab, we find that 2sin2(θ23)sin2(2θ13)<0.12(0.20) at 90% confidence level for δ=0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin2(θ23)sin2(2θ13)=0.041+0.047−0.031(0.079+0.071−0.053). The θ13=0 hypothesis is disfavored by the MINOS data at the 89% confidence level.

We report on νe and ν⎯⎯e appearance in νμ and ν⎯⎯μ beams using the full MINOS data sample. The comparison of these νe and ν⎯⎯e appearance data at a 735 km baseline with θ13 measurements by reactor experiments probes δ, the θ23 octant degeneracy, and the mass hierarchy. This analysis is the first use of this technique and includes the first accelerator long-baseline search for ν⎯⎯μ→ν⎯⎯e. Our data disfavor 31% (5%) of the three-parameter space defined by δ, the octant of the θ23, and the mass hierarchy at the 68% (90%) C.L. We measure a value of 2sin2(2θ13)sin2(θ23) that is consistent with reactor experiments.