University of Minnesota
School of Physics & Astronomy
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Cheng-Hsien Li

MCNAMARAC 141 (office)
cli @ physics.umn.edu

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Summary of Interests
Neutrino oscillations with three flavors and CP violation

About My Work

It has been observed in various experiments that neutrinos oscillate among different flavors due to the fact that the weak interaction eigenstates are linear combinations of the mass eigenstates. This is among the most important discoveries in physics beyond the standard model. The neutrino mixing matrix, similar to the CKM matrix for quarks, is characterized by three vacuum mixing angles, one Dirac or three Majorana CP violation phases. In addition, the three neutrino masses give two independent mass-squared differences that govern various channels of flavor oscillations. Many experiments have been performed or are being planned to determine the mixing angles, the CP violation phases, and the mass hierarchy, with the latter two kinds of parameters being largely unknown so far.

New phenomena of neutrino oscillations arise when neutrinos propagate in matter, especially with varying matter density in the Sun or a supernova, due to the Mikheyev-Smirnov-Wolfenstein (MSW) effect. Thus, experiments on the earth and observations of solar and supernova neutrinos provide different venues to examine neutrino oscillations. It is crucial to understand, with the assumed mixing parameters, how neutrinos oscillate from one flavor to another in various environments.

I am currently working with Professor Yong-Zhong Qian (continuing through this summer) to develop a numerical code to solve for neutrino oscillations with three flavors and CP violation and eventually including matter effect. The 2x2 mixing of electron and muon neutrinos can be solved analytically. However, the mixing of 3 types of neutrinos with CP violation and matter effect adds much complexity. As the first step, I aim to solve the problem of neutrino oscillations in vacuum and in matter with constant density. Such solutions can be immediately applied to and verified by long-baseline experiments on the earth such as MINOS and NOvA. Then the solution will be extended to account for varying matter density in astrophysical environments where the MSW effect must be taken into account. The outcome of this project could be a step toward the search for effects of CP violation in supernovae.

Education

B.S., National Tsing Hua University, Hsinchu, Taiwan, 2008