Prospects for cosmic neutrino detection in tritium experiments in the case of hierarchical neutrino masses

We discuss the effects of neutrino mixing and the neutrino mass hierarchy when considering the capture of the cosmic neutrino background (CNB) on radioactive nuclei. The implications of mixing and hierarchy at future generations of tritium decay experiments are considered. We find that the CNB should be detectable at these experiments provided that the resolution for the kinetic energy of the outgoing electron can be pushed to a few 0.01 eV for the scenario with inverted neutrino mass hierarchy, about an order of magnitude better than that of the upcoming KATRIN experiment. Another order of magnitude improvement is needed in the case of normal neutrino mass hierarchy. We also note that mixing effects generally make the prospects for CNB detection worse due to an increased maximum energy of the normal beta decay background.

Figure 1

Event rates as functions of the kinetic energy $T_e$ of the electron for inverted hierarchy, ${\theta }_{13}=0$, and Gaussian detector resolution $\Delta$. The bold (thin) curves correspond to the CNB signal (beta decay background) and we have assumed a negligible gravitational clustering.

Figure 2

Event rates as functions of the kinetic energy $T_e$ of the electron for the normal hierarchy, ${\theta }_{13}=0$, and a Gaussian detector resolution of $\Delta =0.008\mathrm{eV}$. The bold (thin) curves correspond to the CNB signal (beta decay background) and we have assumed a negligible gravitational clustering.

Figure 3

Event rates as functions of the kinetic energy $T_e$ of the electron for inverted hierarchy, different ${\theta }_{13}$, and Gaussian detector resolution $\Delta =0.03\mathrm{eV}$. The bold (thin) curves correspond to the CNB signal (beta decay background) and we have assumed a negligible gravitational clustering (c.f., Fig. 1).

Figure 4

Event rates as functions of the kinetic energy $T_e$ of the electron for inverted hierarchy, ${\theta }_{13}=10°$, and Gaussian detector resolution $\Delta$. The bold (thin) curves correspond to the CNB signal (beta decay background) and we have assumed a negligible gravitational clustering.