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Constraints on Oscillation Parameters from ν_{e} Appearance and ν_{μ} Disappearance in NOvA
P Adamson1, L Aliaga1, D Ambrose2
1Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA.
Physical Review Letters
|June 24, 2017
Summary
The NOvA experiment improved measurements of muon neutrino to electron neutrino transitions. Results disfavor the inverted mass hierarchy, a key finding in neutrino physics.
Area of Science:
- Particle Physics
- Neutrino Oscillations
- High-Energy Physics
Background:
- Neutrino oscillations are a key phenomenon in particle physics, offering insights into neutrino mass and mixing.
- Understanding the neutrino mass ordering (normal vs. inverted hierarchy) and the value of the CP-violating phase (δCP) are crucial for a complete Standard Model.
- The NOvA experiment is a long-baseline neutrino oscillation experiment designed to measure these parameters with high precision.
Purpose of the Study:
- To report improved measurements of muon neutrino (νμ) to electron neutrino (νe) transitions using the NOvA detector.
- To constrain the neutrino mass hierarchy and the atmospheric mixing angle θ23 using a large dataset.
- To test the hypothesis of an inverted neutrino mass hierarchy.
Main Methods:
- Utilized an exposure of 6.05×10^20 protons on target (POT) at the NOvA detector.
- Identified and analyzed 33 candidate events for νμ→νe transitions, with a well-characterized background of 8.2±0.8 (syst.).
- Combined the νμ→νe data with NOvA's νμ disappearance data and external constraints on sin²2θ13 from reactor experiments.
Main Results:
- Observed 33 electron neutrino candidates with a systematic uncertainty of 0.8.
- The data, when combined with other measurements, disfavors the inverted mass hierarchy hypothesis.
- The disfavoring of the inverted mass hierarchy holds for all possible values of the CP-violating phase, δCP, at a confidence level greater than 93%.
Conclusions:
- The improved measurement of νμ→νe transitions provides significant constraints on neutrino properties.
- The results challenge the inverted mass hierarchy model, favoring the normal mass hierarchy.
- This study contributes to the ongoing effort to fully characterize neutrino mixing parameters and CP violation.
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