Diagnosing the reactor antineutrino anomaly with global antineutrino flux data

We have examined the impact of new Daya Bay, Double Chooz, and RENO measurements on global fits of reactor antineutrino flux data to a variety of hypotheses regarding the origin of the reactor antineutrino anomaly. In comparing RENO and Daya Bay measurements of inverse beta decay (IBD) yield versus ${}^{239}\mathrm{Pu}$ fission fraction, we find differing levels of precision in measurements of time-integrated yield and yield slope, but similar central values, leading to modestly enhanced isotopic IBD yield measurements in a joint fit of the two datasets. In the absence of sterile neutrino oscillations, global fits to all measurements now provide $3\sigma$ preference for incorrect modeling of specific fission isotopes over common mismodeling of all beta-converted isotopes. If sterile neutrino oscillations are considered, global IBD yield fits provide no substantial preference between oscillation-including and oscillation-excluding hypotheses: hybrid models containing both sterile neutrino oscillations and incorrect ${}^{235}\mathrm{U}$ or ${}^{239}\mathrm{Pu}$ flux predictions are favored at only $1\sigma –2\sigma$ with respect to models where ${}^{235}\mathrm{U}$, ${}^{238}\mathrm{U}$, and ${}^{239}\mathrm{Pu}$ are assumed to be incorrectly predicted.

Figure 1

Top: Daya Bay and RENO IBD yield measurements versus effective ${}^{239}\mathrm{Pu}$ fission fraction $F_{239}$. Error bars on each point represent statistical errors, while bands overlaying each dataset represent correlated uncertainties. Bottom: Measured and Huber-Mueller-predicted [1, 2] time-averaged IBD yields ${\overline{\sigma }}_f$ and yield slopes ($\frac{d{\sigma }_f}{d{F}_{239}}$). A small predicted difference between Daya Bay and RENO ${\overline{\sigma }}_f$ due to differing average fission fractions is indicated by a thicker central value band.

Figure 2

Allowed regions for isotopic IBD yields of ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$ provided by fits of updated Daya Bay and new RENO flux evolution results. Gray horizontal and vertical lines represent Huber-Mueller-predicted central values.

Figure 3

Allowed regions for isotopic IBD yields of ${}^{235}\mathrm{U}$, ${}^{239}\mathrm{Pu}$, and ${}^{238}\mathrm{U}$ provided by a fit of all IBD yield datasets to the $\mathbf{235}\mathbf{+}\mathbf{239}\mathbf{+}\mathbf{238}$ hypothesis described in the text. The blue solid, dashed and dotted contours show the previous $235+239+238$ regions obtained in Ref. [19] at $1\sigma$, $2\sigma$, and $3\sigma$, respectively. Gray horizontal and vertical lines represent Huber-Mueller-predicted central values.

Figure 4

$1\sigma$, $2\sigma$, and $3\sigma$ allowed oscillation parameter space regions for scenarios involving sterile neutrinos and incorrectly predicted fluxes from ${}^{235}\mathrm{U}$ (center), ${}^{239}\mathrm{Pu}$ (right), or neither isotope (left). Allowed $1\sigma$ (solid), $2\sigma$ (dashed), and $3\sigma$ (dotted) parameter space regions for the separate Daya Bay and RENO flux evolution datasets (blue) and global rate datasets (red) are also included. As baseline information is not considered for the fit of flux evolution data, its allowed regions are vertical bands, with thick dash-dotted lines indicating best-fit values.