We investigated the potential of the energy resolving hybrid pixel detector Timepix contacted to a CdTe sensor layer for the search for the neutrinoless double-beta decay of . We found that a CdTe sensor layer with 3？mm thickness and 165？μm pixel pitch is optimal with respect to the effective Majorana neutrino mass ( ) sensitivity. In simulations, we were able to demonstrate a possible reduction of the background level caused by single electrons by approximately 75% at a specific background rate of 10？3 counts/( ) at a detection efficiency reduction of about 23% with track analysis employing random decision forests. Exploitation of the imaging properties with track analysis leads to an improvement in sensitivity to by about 22%. After 5 years of measuring time, the sensitivity to of a 420？kg CdTe experiment (90% enrichment) would be 59？meV on a 90% confidence level for a specific single-electron background rate of 10？3 counts/( ). The α-particle background can be suppressed by at least about six orders of magnitude. The benefit of the hybrid pixel detector technology might be increased significantly if drift-time difference measurements would allow reconstruction of tracks in three dimensions. 1. Introduction The question of whether or not neutrinos are their own antiparticles still has not been answered. In many experiments, researchers have to cope with large backgrounds to be able to see if neutrinoless double-beta decay ( ) occurs in nature or not. An observation of one single neutrinoless double-beta decay would directly prove the Majorana character of neutrinos via the Schechter-Valle theorem [1]. Besides this, a measurement of the decay rate (or the half-life ) of neutrinoless double-beta decay allows the determination of the effective Majorana neutrino mass which is given by where is the electron rest mass, is the calculable factor for the decay specific phase-space volume, is also the calculable nuclear matrix element, and the are elements of the mixing matrix which describes neutrino mixing of the three mass eigenstates with masses to the electron neutrino. is the nuclear charge and is the -value of the double-beta decay. Thus, a measurement of the half-life of -decay gives information on the masses of the mass eigenstates and the elements of the mixing matrix which depends on the mixing angles , , and potentially on CP-violating phases [2]. If neutrinos are Majorana fermions, two Majorana phases and appear in the mixing matrix in addition to the Dirac phase . In the Majorana case the mixing matrix reads where is the Standard Model PMNS-matrix
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