First Measurement of Electron Neutrino Appearance in NOvA
Figure 1: (Inset) Scheme of the NOvA beam line. A neutrino beam, generated at the Fermilab accelerator complex, propagates 810 km through the Earth to reach the 14-kiloton "far detector" in northern Minnesota. (Main) NOvA data recorded in the far detector volume for 5 milliseconds, showing thousands of cosmic-ray particle tracks. [Credit: NOvA]
The first results from the NOvA experiment, which set new constraints on charge-parity violation in neutrinos and on the ordering of neutrino masses, have been reported in the latest issue of Physical Review Letters*. These results are from the first search for νμ → νe transitions. In an exposure equivalent to 2.74 × 1020 protons on target in the upgraded NuMI beam at Fermilab, the NOvA team observed 6 events in the Far Detector, compared to a background expectation of 0.99 ± 0.11 (syst) events based on the Near Detector measurement. A secondary analysis observed 11 events with a background of 1.07 ± 0.14 (syst). The 3.3σ excess of events observed in the primary analysis disfavors 0.1π <δCP 0.5π in the inverted mass hierarchy at the 90% C.L.
Prof. Gary Feldman, engineer Nathan Felt, grad student Gareth Kafka, and research scholars John Oliver, Raphaël Schroeter and Ruth Toner are among the authors of the paper*, which is featured in APS Physics: Joshua B. Spitz, "Ghostly Neutrino Comes into Sharper Focus, Physics 9, 39
*Adamson et al. (NOvA Collaboration), "First Measurement of Electron Neutrino Appearance in NOvA,"Physical Review Letters 116, 151806 | DOI: http://dx.doi.org/10.1103/PhysRevLett.116.151806