# New Realization of the Conversion Calculation for Reactor Antineutrino Fluxes

## TL;DR

This paper introduces a new method for calculating reactor antineutrino fluxes that accounts for both allowed and forbidden beta decay branches, reducing biases and improving prediction accuracy based on nuclear database data.

## Contribution

The paper proposes a novel conversion calculation method incorporating forbidden decays, validated with simulated and real data, enhancing flux prediction reliability.

## Key findings

- Neglecting shape variation causes significant bias in flux calculations.
- The new method reduces rate and spectral biases.
- Accurate high-energy beta decay data is crucial for reliable predictions.

## Abstract

Validation of the effective conversion method in the reactor antineutrino flux calculation is examined using the \textit{ab initio} calculation of the electron and antineutrino spectra from the state-of-the-art nuclear database. It turns out that neglecting the shape variation of beta decay branches between the allowed and forbidden transitions would induce significant bias in the total inverse-beta-decay yields and energy spectral distributions. We propose a new realization of the conversion method with both the allowed and forbidden virtual branches, and apply it to both the \textit{simulated} data from the nuclear database and \textit{real} data from the fission measurements at ILL by virtue of statistical properties of the allowed and forbidden decays in the database. Two kinds of dominant uncertainty sources are identified and it turns out that the new realization of the conversion calculation can largely reduce the rate and spectral bias and thus present a reliable prediction of the antineutrino fluxes if accurate beta decay information is available in the high endpoint energy range.