First Measurement of High-Energy Reactor Antineutrinos at Daya Bay
Fengpeng An, Weidong Bai, A. B. Balantekin, M. Bishai, S. Blyth, G. F. Cao, Jun Cao, J. F. Chang, Y. Chang, H S Chen, H. Chen, S M Chen, Y. Chen, Y X Chen, Jie Cheng, Zhaokan Cheng, J. J. Cherwinka, M. C. Chu, J. P. Cummings, Olivia Dalager, F. S. Deng, Ying Ding, M. Diwan, Tadeáš Dohnal, Dmitry Dolzhikov, J. Dove, D. A. Dwyer, J. P. Gallo, M. Gonchar, G. Gong, Haipeng Gong, W. Gu, J. Y. Guo, Lei Guo, Xin-Heng Guo, Yuhang Guo, Ziyi Guo, R. Hackenburg, S. Hans, M. He, K. M. Heeger, Y. K. Heng, Y. K. Hor, Y. Hsiung, Beibei Hu, Jun Hu, T. Hu, Z. 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, Li-Wei 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, Qiang Li, R H Li, S. Li, S. Li, W D Li, X N Li, X. Li, Y F Li, Zongwang Li, Han Liang, C.-J. Lin, Guey-Lin Lin, S. Lin, J. J. Ling, J. M. Link, L. Littenberg, B. R. Littlejohn, J C Liu, Jianglai Liu, Jin Liu, C. Lu, H. Q. Lu, X.-G. Lu, B Z, X B, X Y, Y Q, R. C. Mandujano
Abstract
This Letter reports the first measurement of high-energy reactor antineutrinos at Daya Bay, with nearly 9000 inverse beta decay candidates in the prompt energy region of 8-12 MeV observed over 1958 days of data collection. A multivariate analysis is used to separate 2500 signal events from background statistically. The hypothesis of no reactor antineutrinos with neutrino energy above 10 MeV is rejected with a significance of 6.2 standard deviations. A 29% antineutrino flux deficit in the prompt energy region of 8-11 MeV is observed compared to a recent model prediction. We provide the unfolded antineutrino spectrum above 7 MeV as a data-based reference for other experiments. This result provides the first direct observation of the production of antineutrinos from several high-Q_{β} isotopes in commercial reactors.