报告题目：The Neutrino CP measurements: Dirac & Majorana
报告人： 葛韶锋博士（日本东京大学 Kavli IPMU)
The leptonic Dirac CP phase has profound physical consequences due to its connection with leptogenesis for explaining the existence of matter in the Universe. To some extent, the leptonic CP phase is even more important than the Higgs boson that provide mass for all fundamental particles. If we cannot understand the existence of matter, why we need to care about their mass.
I will first review the status of CP measurement and then introduce a new proposal with muon decay at rest (muDAR). Currently, accelerator neutrino experiments such as T2K, NOvA, and DUNE are the most promising for CP measurement. Nevertheless, they suffer from several problems of degeneracy, efficiency, sensitivity, and new physics such as non-unitarity mixing (NUM) and (vector, scalar, dark) non-standard interactions (NSI). The situation can be improved by adding a muon decay at rest (muDAR) source. With T2(H)K running in neutrino mode and muDAR in anti-neutrino mode, both using the same detector, the CP measurement becomes more precise can break the degeneracy between \delta and 180^o - \delta. Most importantly, muDAR can guarantee the CP sensitivity against NUM and NSI. The same configuration can also apply to next-generation medium baseline reactor neutrino experiments like JUNO and RENO-50, enhancing their physics potential from just mass hierarchy to also CP. With only one source and no extra detectors, this dessign is much better than DAEdLAS which requires 3 sources, but only 20% duty factor and 4 times higher luminosity for each.
If neutrinos are Majorana particles, there is not just one Dirac CP phase, but also two Majorana CP phases. The nature of Majorana neutrinos can be probed in the neutrinoless double beta (0v2b) decay. Unfortunately, current global fit from neutrino oscillation experiments and cosmological observations indicate that the neutrino mass hierarchy should be normal. This seems not good for observing the 0v2b decay. But I will demonstrate that the situation is actually the opposite. The normal hierarchy can allow simultaneous determination of the two Majorana CP phases, which can never be true for the inverted mass hierarchy.