Research

# Neutrino Physics

## Searching for the neutrinoless double beta decay with EXO-200 and nEXO

### EXO-200

Are neutrinos Dirac- or Majorana-fermions? Still today, this question has not been answered although huge efforts have been made to search for neutrinoless double beta decay which is the most practical way to get an answer. Furthermore, a possible detection of this decay could give valuable information about the masses of the neutrino mass eigenstates as the half-life depends on the effective Majorana neutrino mass. The Enriched Xenon Observatory EXO-200 has carried out one of the most sensitive searches for this decay channel in 136Xe with two years of data. The EXO-200 detector is a double-sided, single-phase liquid xenon time-projection-chamber. EXO-200 started a second phase of data taking in April 2016. More information can be found here.

### nEXO

The next-generation, tonne-scale experiment nEXO (next generation Enriched Xenon Observatory) is the successor of EXO-200 and will have 25 times more mass than EXO-200.  With its single-sided, single-phase time-projection-chamber filled with 5 tonnes of enriched liquid xenon nEXO will be able to probe the possible effective Majorana neutrino masses in the inverted mass hierarchy regime. Light-detection in nEXO will be carried out with silicon photomultipliers. The charge measurement will be realized with a checkerboard style electrode matrix. With the projected energy resolution of 1% (sigma) at the Q-value of the decay, nEXO aims at a half-life sensitivity of 6.2x 10^27 years at 90% C.L. after 5 years of measuring time. nEXO will be able to fully test the possible effective Majorana neutrino masses in the scenario of a inverted neutrino mass hierarchy. More information can be found here.

## Measuring the neutrino mass hierarchy with KM3NeT-ORCA

With the ORCA (Oscillation Research with Cosmics in the Abyss) detector the KM3NeT collaboration will study a fundamental question of particle physics: that of the relative ordering of the neutrino masses, also referred to as the neutrino mass hierarchy. The influence of the mass hierarchy on neutrino oscillations in matter leaves its imprint on the atmospheric neutrino flux. The first construction phase of ORCA has started and the full detector could be operational towards 2020. With three years of data taking ORCA will resolve the neutrino mass hierarchy with a median significance of about 3 sigma (370:1). More information can be found here.