Model for the Cherenkov light emission of TeO 2 cryogenic calorimeters

The most sensitive process able to probe the Majorana nature of neutrinos and discover Lepton Number Violation is the neutrino-less double beta decay. Thanks to the excellent energy resolution, efficiency and intrinsic radio-purity, cryogenic calorimeters are primed for the search for this process. A novel approach able to improve the sensitivity of the current experiments is the rejection of $alpha$ interactions, that represents the dominant background source. In TeO$_2$ calorimeters, $alpha$ particles can be tagged as, in contrast to electrons, they do not emit Cherenkov light. Nevertheless, the very low amount of detected Cherenkov light undermines the complete rejection of $alpha$ background. In this paper we compare the results obtained in previous measurements of the TeO$_2$ light yield with a detailed Monte Carlo simulation able to reproduce the number of Cherenkov photons produced in $eta/gamma$ interactions within the calorimeter and their propagation in the experimental set-up. We demonstrate that the light yield detectable from a $5 imes5 imes5$~cm$^3$ TeO$_2$ bolometer can be increased by up to 60% by increasing the surface roughness of the crystal and improving the light detector design. Moreover, we study the possibility to disentangle $alpha$, $eta$ and $gamma$ interactions, which represent the ultimate background source. Unfortunately $gamma$ rejection is not feasible but $alpha$ rejection can be achieved exploiting high sensitivity light detectors.