# Fuel-Composition Dependent Reactor Antineutrino Yield at RENO

Bak, G. (Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea) ; Choi, J. H. (Institute for High Energy Physics, Dongshin University, Naju 58245, Korea) ; Jang, H. I. (Department of Fire Safety, Seoyeong University, Gwangju 61268, Korea) ; Jang, J. S. (GIST College, Gwangju Institute of Science and Technology, Gwangju 61005, Korea) ; Jeon, S. H. (Department of Physics, Sungkyunkwan University, Suwon 16419, Korea) ; Joo, K. K. (Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea) ; Ju, K. (Department of Physics, KAIST, Daejeon 34141, Korea) ; Jung, D. E. (Department of Physics, Sungkyunkwan University, Suwon 16419, Korea) ; Kim, J. G. (Department of Physics, Sungkyunkwan University, Suwon 16419, Korea) ; Kim, J. H. (Department of Physics, Sungkyunkwan University, Suwon 16419, Korea) ; Kim, J. Y. (Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea) ; Kim, S. B. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Kim, S. Y. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Kim, W. (Department of Physics, Kyungpook National University, Daegu 41566, Korea) ; Kwon, E. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Lee, D. H. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Lee, H. G. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Lee, Y. C. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Lim, I. T. (Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea) ; Moon, D. H. (Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea) ; Pac, M. Y. (Institute for High Energy Physics, Dongshin University, Naju 58245, Korea) ; Park, Y. S. (Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea) ; Rott, C. (Department of Physics, Sungkyunkwan University, Suwon 16419, Korea) ; Seo, H. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Seo, J. W. (Department of Physics, Sungkyunkwan University, Suwon 16419, Korea) ; Seo, S. H. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Shin, C. D. (Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea) ; Yang, J. Y. (Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea) ; Yoo, J. (Institute for Basic Science, Daejeon 34047, Korea) (Department of Physics, KAIST, Daejeon 34141, Korea) ; Yu, I. (Department of Physics, Sungkyunkwan University, Suwon 16419, Korea)

12 June 2019

Abstract: We report a fuel-dependent reactor electron antineutrino (${\overline{\nu }}_{e}$) yield using six $2.8\text{}{\mathrm{GW}}_{\mathrm{th}}$ reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The analysis uses 850 666 ${\overline{\nu }}_{e}$ candidate events with a background fraction of 2.0% acquired through inverse beta decay (IBD) interactions in the near detector for 1807.9 live days from August 2011 to February 2018. Based on multiple fuel cycles, we observe a fuel ${}^{235}U$ dependent variation of measured IBD yields with a slope of $\left(1.51±0.23\right)×{10}^{-43}\text{}\text{}{\mathrm{cm}}^{2}/\mathrm{fission}$ and measure a total average IBD yield of $\left(5.84±0.13\right)×{10}^{-43}\text{}\text{}{\mathrm{cm}}^{2}/\mathrm{fission}$. The hypothesis of no fuel-dependent IBD yield is ruled out at $6.6\sigma$. The observed IBD yield variation over ${}^{235}U$ isotope fraction does not show significant deviation from the Huber-Mueller (HM) prediction at $1.3\text{}\sigma$. The measured fuel-dependent variation determines IBD yields of $\left(6.15±0.19\right)×{10}^{-43}$ and $\left(4.18±0.26\right)×{10}^{-43}\text{}\text{}{\mathrm{cm}}^{2}/\mathrm{fission}$ for two dominant fuel isotopes ${}^{235}U$ and ${}^{239}\mathrm{Pu}$, respectively. The measured IBD yield per ${}^{235}U$ fission shows the largest deficit relative to the HM prediction. Reevaluation of the ${}^{235}U$ IBD yield per fission may mostly solve the reactor antineutrino anomaly (RAA) while ${}^{239}\mathrm{Pu}$ is not completely ruled out as a possible contributor to the anomaly. We also report a $2.9\text{}\sigma$ correlation between the fractional change of the 5 MeV excess and the reactor fuel isotope fraction of ${}^{235}U$.

Published in: Physical Review Letters 122 (2019)