Search for a time-varying electron antineutrino signal at Daya Bay

TL;DR

This study analyzed 621 days of Daya Bay neutrino data to search for time-varying electron antineutrino signals and Lorentz/CPT violation, finding no significant signals but setting new experimental limits on these phenomena.

Contribution

First experimental constraints on Lorentz and CPT violation for three neutrino flavor pairs using Daya Bay's unique multi-directional setup.

Findings

No significant time-varying antineutrino signals detected.

Set new limits on Lorentz and CPT violation parameters.

First to constrain all six flavor pairs individually.

Abstract

A search for a time-varying $\bar{\nu}_{e}$ signal was performed with 621 days of data acquired by the Daya Bay Reactor Neutrino Experiment over 704 calendar days. The time spectrum of the measured $\overline{\nu}_e$ flux normalized to its prediction was analyzed with a Lomb-Scargle periodogram, which yielded no significant signal for periods ranging from 2 hours to nearly 2 years. The normalized time spectrum was also fit for a sidereal modulation under the Standard Model extension (SME) framework to search for Lorentz and CPT violation (LV-CPTV). Limits were obtained for all six flavor pairs $\bar{e}\bar{\mu}$, $\bar{e}\bar{\tau}$, $\bar{\mu}\bar{\tau}$, $\bar{e}\bar{e},\bar{\mu}\bar{\mu}$ and $\bar{\tau}\bar{\tau}$ by fitting them one at a time, constituting the first experimental constraints on the latter three. Daya Bay's high statistics and unique layout of multiple directions from three pairs of reactors to three experimental halls allowed the simultaneous constraint of individual SME LV-CPTV coefficients without assuming others contribute negligibly, a first for a neutrino experiment.