A Study of Invisible Neutrino Decay at DUNE and its Effects on ${\theta }_{23}$ Measurement

Abstract

We study the consequences of invisible decay of neutrinos in the context of the DUNE experiment. We assume that the third mass eigenstate is unstable and decays to a light sterile neutrino and a scalar or a pseudo-scalar. We consider DUNE running in 5 years neutrino and 5 years antineutrino mode and a detector volume of 40 kt. We obtain the bounds on the rest frame life time ${\tau }_3$ normalized to the mass $m_3$ as ${\tau }_3/m_3>4.50\times 10^{-11}$ s/eV at 90\% C.L. for a normal hierarchical mass spectrum. We also find that DUNE can discover neutrino decay for ${\tau }_3/m_3>4.27\times 10^{-11}$ s/eV at 90\% C.L. In addition, for an unstable ${\nu }_3$ with an illustrative value of ${\tau }_3/m_3$ = $1.2\times 10^{-11}$ s/eV, the no decay case gets disfavoured at the $3\sigma$ C.L. At 90\% C.L. the allowed range for this true value is obtained as $1.71\times 10^{-11}>{\tau }_3/m_3>9.29\times 10^{-12}$ in units of s/eV. We also study the correlation between a non-zero ${\tau }_3/m_3$ and standard oscillation parameters and find an interesting correlation in the appearance channel probability with the mixing angle ${\theta }_{23}$. This alters the octant sensitvity of DUNE, favorably (unfavorably) for true ${\theta }_{23}$ in the lower (higher) octant. The effect of a decaying neutrino does not alter the hierarchy or CP discovery sensitivity of DUNE in a discernible way.

Comments: accepted and published in JHEP with additional figures and few references