Reactor Neutrino Anomalies and Possible Solutions Yu-Feng Li* Institute of High Energy Physics, Beijing, China *corresponding author: liyufeng@ihep.ac.cn Reactor neutrinos (electron antineutrinos) are produced from beta decays of the neutron-rich fission products, and are detected via the inverse beta decay (IBD) process. Reactor experiments have shown anomalous results for both IBD rate (left plot) and spectrum (right plot) measurements Reactor rate anomaly: measured IBD yields are smaller than model predictions by around 6%. Reactor spectrum anomaly: there is a bump at around 5 MeV when comparing the measured and predicted spectra. How to solve these reactor anomalies is an intensively discussed topic in nuclear and particle physics community. 1. Reactor neutrino anomalies 3. Ab initial method Using the reactor rates data and fuel evolution data: 2. Data-driven method Reactor rates tend to favor equal suppression of the 235U and 239Pu fluxes (oscillation), while (DYB & RENO) fuel evolution data favor the suppression of 235U. Regarding all hybrid hypotheses: a) a deficit for the 235U flux is always obtained; b) oscillation-including hypothesis is favored over the oscillation-excluding one: moderately at 1-2σ 5. Conversion method Giunti et al., JHEP 10 (2017) 143 4. Beta decay at KATRIN 6. Conclusion Reactor rate/spectrum anomalies are interesting topics in particle and nuclear physics, and awaiting satisfactory solutions. Data-driven method always favors a suppression of the 235U flux, while KATRIN can provide independent tests. Both the ab initial and conversion calculations need to be improved in many aspects (database, fission yield and single spectrum, etc.). Accurate reactor rate and spectrum predictions are important for future reactor experiments (i.e., JUNO). Giunti et al., Phys. Rev.D 99 (2019) 073005 Ab initial model for the reactor neutrino flux: summation of each beta decay branches using the nuclear database for the fission and decay information Possible problems: the nuclear database (e.g., pandemonium effect), fission yield, single beta decay spectrum, etc. We discuss the effects of the single beta decay spectrum by using a fully numerical calculation of lepton wave functions, compared to previous ones using the famous Fermi function. Fang, et al., arXiv: 2001.01689 ENDF VIII.0, for fission yield data, and ENSDF for the decay data. 2% and 4% deviations for the neutrino and electron spectra. Beta decay is a model-independent way to probe the absolute neutrino masses. KATRIN published its first data in 2019, with a limit on the effective neutrino mass as mν< 1.1 eV (95% C.L.). We test the reactor rate anomaly using the beta decay data at KATRIN by assuming the 3+1 active-sterile mixing. KATRIN improves the exclusion of the large-Δm2 41 solution of the Huber-Muller reactor rate anomaly. RSR: the reactor spectra ratio data test a large part of the small-Δm2 41 region. Tritium: KATRIN + Mainz + Troitsk RSR and Tritium limits are complementary, and rule out most of the parameter space. Giunti et al., JHEP 05 (2020) 061 Conversion model for the reactor neutrino flux: using dozens of virtual beta decay branches to fit the aggregate electron spectra of 235U, 239Pu, and 241Pu at ILL. We propose a new realization of the conversion calculation by including the contribution of forbidden decay branches. Using data of ILL U235 beta spectrum Li, et. al., Phys. Rev. D 100 (2019), 053005 7. Reference [1] G. Mention et al., Phys. Rev. D 83 (2011) 073006. [2] T.A. Mueller et al., Phys. Rev. C 832011) 054615. [3] P. Huber, Phys. Rev. C 84 (2011) 024617. [4] KATRIN, Phys. Rev. Lett. 123 (2019) 221802. [5] C. Giunti et al., Phys. Rev. D 99 (2019) 073005. [6] Y.F. Li, D. Zhang, Phys. Rev. D 100 (2019) 053005. [7] D.L. Fang et al., arXiv: 2001.01689. [8] C. Giunti et al., JHEP 05 (2020) 061.