Improved Measurement of the Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay
Fengpeng An, W. D. Bai, A. B. Balantekin, M. Bishai, S. Blyth, G. F. Cao, Jun Cao, J. F. Chang, Y. Chang, S. Chen, H. Y. Chen, Shaomin Chen, Y. Chen, Y. X. Chen, J. Cheng, Jie Cheng, Yi-Ting Cheng, Zhaokan Cheng, J. J. Cherwinka, M. C. Chu, J. P. Cummings, Olivia Dalager, F. S. Deng, Yayun Ding, M. V. Diwan, T. Dohnal, Dmitry Dolzhikov, J. Dove, Katherine Dugas, Hongyue Duyang, D. A. Dwyer, J. P. Gallo, M. Gonchar, G. Gong, Haiyang Gong, W. Gu, J. Y. Guo, Linghong Guo, X. H. Guo, Yuhang Guo, Ziyi Guo, R. Hackenburg, Yang Han, S. Hans, M. He, K. M. Heeger, Y. K. Heng, Y. K. Hor, Y. Hsiung, Beibei Hu, Jun Hu, Ting Hu, Zhongfa Hu, Han‐Xiong Huang, Jihong Huang, X. T. Huang, Y. B. Huang, Patrick Huber, D. E. Jaffe, K. L. Jen, X. L. Ji, Xiangpan Ji, R. A. Johnson, D. Jones, Lin Kang, S. H. Kettell, S. Kohn, M. Krämer, T. J. Langford, J. Lee, J. H. C. Lee, R. T. Lei, R. Leitner, J. K. C. Leung, F. Li, H. L. Li, Jinjing Li, Q. J. Li, R. H. Li, Shangrong Li, S. C. Li, W. D. Li, X. N. Li, X. Q. Li, Yufeng Li, Z. B. Li, Hongwei Liang, C.-J. Lin, G. L. Lin, S. Lin, Jiajie Ling, J. M. Link, L. Littenberg, B. R. Littlejohn, J. C. Liu, J. L. Liu, J. X. Liu, C. Lu, H. Q. Lu, K. B. Luk
Abstract
Reactor neutrino experiments play a crucial role in advancing our knowledge of neutrinos. In this Letter, the evolution of the flux and spectrum as a function of the reactor isotopic content is reported in terms of the inverse-beta-decay yield at Daya Bay with 1958 days of data and improved systematic uncertainties. These measurements are compared with two signature model predictions: the Huber-Mueller model based on the conversion method and the SM2018 model based on the summation method. The measured average flux and spectrum, as well as the flux evolution with the ^{239}Pu isotopic fraction, are inconsistent with the predictions of the Huber-Mueller model. In contrast, the SM2018 model is shown to agree with the average flux and its evolution but fails to describe the energy spectrum. Altering the predicted inverse-beta-decay spectrum from ^{239}Pu fission does not improve the agreement with the measurement for either model. The models can be brought into better agreement with the measurements if either the predicted spectrum due to ^{235}U fission is changed or the predicted ^{235}U, ^{238}U, ^{239}Pu, and ^{241}Pu spectra are changed in equal measure.