Programme

P.6 -- Poster, VCTP-49

Date: Wednesday, 31 July 2024

Time: 08:30 - 10:00

Ultimate Precision of the Leptonic Mixing Angle $\theta_{23}$ and its Implications for the Leptonic Flavor Models

Phan To Quyen (1,2), Cao Van Son (2), Nguyen Thi Hong Van (3), Ankur Nath (4), Tran Van Ngoc (5)

(1) Graduate University of Science and Technology, Vietnam Academy of Science and Technology, Hanoi, Viet Nam. (2) Institute for Interdisciplinary Research in Science and Education, ICISE, Quy Nhon, Vietnam. (3) Institute of Physics, Vietnam Academy of Science and Technology, Hanoi, Vietnam. (4) Department of Physics, Namrup College, Assam, India. (5) Department of Physics, Kyoto University, Kyoto, Japan.

Neutrino oscillation, a quantum mechanics phenomenon where one type of neutrino flavor can invert into others when traveling, revealing that neutrinos have mass and that leptons mix, surpasses the explanatory scope of the Standard Model. In the weak interaction basis, neutrino flavor eigenstates ($\nu_{e}, \nu_{\mu}, \nu_{\tau}$) are related to neutrino mass eigenstates ($\nu_{1}, \nu_{2}, \nu_{3}$) through the unitary leptonic mixing matrix $U_{PMNS}$, parameterized by three mixing angles ($\theta_{12}, \theta_{13}, \theta_{23}$) and one CP-violation phase ($\delta_{CP}$), with the precision measurement of $U_{PMNS}$ being one of primary objectives of current and future neutrino experiments. Among the three leptonic mixing angles, the $\theta_{23}$ angle, which characterizes the fractional contribution of the two flavor eigenstates $\nu_{\mu}$ and $\nu_{\tau}$ in the mass eigenstate $\nu_3$, is known to be the largest (close to $\pi/4$) but the least precisely measured. Up-to-date data from neutrino oscillation experiments neither exclude the maximal mixing $\theta_{23}=\pi/4$ hypothesis nor determine distinctly its octant preference. This work revisits the ambiguity in the measurement of this angle in conjunction with other leptonic mixing parameters and investigates its ultimate precision measurement with two upcoming gigantic accelerator-based long-baseline neutrino experiments, Hyper-Kamiokande and DUNE, as well as joint possible future neutrino facilities like ESSnuSB and Neutrino Factory. The implication of this precise measurement of the mixing angle $\theta_{23}$ in examining the leptonic flavor models is also discussed.

Presenter: Phan To Quyen