Updated Summation Model: An Improved Agreement with the Daya Bay Antineutrino Fluxes

Abstract

A new summation method model of the reactor antineutrino energy spectrum is presented. It is updated with the most recent evaluated decay databases and with our Total Absorption Gammaray Spectroscopy measurements performed during the last decade. For the first time the spectral measurements from the Daya Bay experiment are compared with the detected antineutrino energy spectrum computed with the updated summation method without any renormalisation. The results exhibit a better agreement than is obtained with the Huber-Mueller model in the 2 to 5 MeV range, the region which dominates the detected flux. An unexpected systematic trend is found that the detected antineutrino flux computed with the summation model decreases with the inclusion of more Pandemonium free data. The detected flux obtained now lies only 1.9% above that detected in the Daya Bay experiment, a value that may be reduced with forthcoming new Pandemonium free data leaving less and less room to the reactor anomaly. Eventually, the new predictions of individual antineutrino spectra for the 235 U, 239 Pu, 241 Pu and 238 U are used to compute the dependence of the reactor antineutrino spectral shape on the fission fractions.

Reevaluating reactor antineutrino anomalies with updated flux predictions

“…An updated ab initio calculation was recently published in Ref. [28]. There, it was found that ab initio predictions produce better agreement with the ν e spectrum measured at Daya Bay than the HM predictions, This is due, in large part, to a ∼10% reduction in the flux from 235 U, a feature that is consistent with previous findings [29,30].…”

“…In recent years, the beta feeding data have been revisited and improved using Total Absorption Gamma Spectroscopy (TAGS), see e.g. [28]. Furthermore, ab initio calculations are also dependent on a theoretical understanding of forbidden decays.…”

The joint evaluated fission and fusion nuclear data library, JEFF-3.3

“…Examples of such estimates may be found in Refs. [328,329] for the estimation of reactor anti-neutrino spectra and in Ref. [330] for beta (β − and β + ) and (anti-)neutrino spectra.…”

Potential impact of sub-structure on the determination of neutrino mass hierarchy at medium-baseline reactor neutrino oscillation experiments

“…Whereas the summation method overestimates the flux from both, and the associated uncertainties are poorly defined [22]. Nevertheless, summation calculations which incorporate the most recent data have found better agreement with overall flux [35]. In any case regardless of the quality of overall flux prediction, we are forced to use the summation method in this analysis because we aim to estimate the fine structure in the spectrum.…”