Measuring the Leptonic Dirac CP Phase with TNT2K

Abstract

I describe how the TNT2K (Tokai and Toyama to Kamioka) configuration with a muon decay at rest ($\mu$DAR) add-on to T2(H)K can achieve better measurement of the leptonic Dirac CP phase $\delta_D$. It has five-fold advantages of high efficiency, smaller CP uncertainty, absence of degeneracy, as well as guaranteeing CP sensitivity against non-unitary mixing (NUM) and non-standard interaction (NSI). In comparison to the flux upgrade with T2K-II, the detector upgrade with T2HK, and the baseline upgrade with T2HKK, TNT2K is a totally different concept with spectrum upgrade to solve the intrinsic problems in current and next generations of CP measurement experiments. With a single $\mu$DAR source, TNT2K is much cheaper and technically much easier than the DAE$\delta$ALUS proposal. The latter needs three sources that cannot run simultaneously and consequently requires much higher fluxes. The single $\mu$DAR source at TNT2K also allows a single near detector ($\mu$Near) to fully utilize the neutrino flux for the purpose of constraining NUM, but this is impossible at DAE$\delta$ALUS with three spatially separated sources.