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

## TL;DR

This paper introduces an improved summation model for reactor antineutrino spectra, incorporating recent decay data and measurements, achieving better agreement with Daya Bay observations and reducing the reactor antineutrino anomaly.

## Contribution

The paper presents a new summation method model updated with recent decay data and measurements, providing more accurate antineutrino spectra without renormalization and reducing the reactor anomaly.

## Key findings

- Better agreement with Daya Bay data in 2-5 MeV range.
- Detected flux only 1.9% above Daya Bay measurements.
- Flux decreases with more Pandemonium free data.

## 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 Gamma-ray 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.