News

The SNSF Swiss Postdoctoral Fellowship was awarded to our group member Florian Jörg, for the "application of radon mitigating surface coatings in a large scale liquid xenon detector". The project aims to reduce radioactive radon backgrounds in future liquid xenon detectors used to search for dark matter and neutrinoless double beta decay. The electrochemical plating method is jointly developed with the Max-Planck-Institut for nuclear physics in Heidelberg (Germany) and will be validated for the first time in a large detector environment at the University of Zurich.

We congratulate former postdoctoral researcher Dr. Christian Wittweg on starting his new academic position as Assistant Professor at Imperial College London in December 2025.

Christian is working on direct dark matter searches and neutrino physics with xenon detectors. He specialises in data analysis and the development of new calibration sources for neutrinoless double-beta decay searches. This work will contribute to the realisation of the future XLZD astroparticle physics observatory. 

Additionally, he is working on low-energy nuclear recoil detection based on permanent crystal lattice defects. This new method is currently being developed for fundamental research on dark matter and neutrinos, but also has potential applications in neutron spectroscopy, dating and measurements of coherent neutrino-nucleus scattering from various sources.

The LEGEND collaboration has published its first results in Physical Review Letters in the search for neutrinoless double-beta (0νββ) decay of ⁷⁶Ge, a major step in determining whether neutrinos are their own antiparticles (i.e. Majorana particles).
Observing this hypothetical process, which violates lepton number conservation by two units, would support mechanisms such as leptogenesis, which could explain the matter–antimatter asymmetry observed in the Universe.

The analysis combines data from the GERDA, MAJORANA DEMONSTRATOR, and LEGEND-200, with the latter contributing 61.0 kg·yr of exposure. No signal was observed, resulting in a new limit on the ⁷⁶Ge 0νββ decay half-life of T_1/2>1.9 × 10²⁶ yr (90% C.L.), reaching a world-leading sensitivity of 2.8 x 10²⁶ yr. This corresponds to an upper limit on the effective Majorana neutrino mass of m_ββ<75–200 meV, depending on the selected nuclear matrix element.

With these first results, LEGEND-200 has demonstrated excellent performance of 142 kg of ⁷⁶Ge-enriched diodes, providing crucial experience for the final phase, LEGEND-1000.

The characterization work carried out by our group on a new photosensor model manufactured by Hamamatsu has been published in JINST.

Time Projection Chamber detectors using xenon (gas and liquid) as active target are widely used in direct dark matter detection experiments. These detectors use photosensors (typically photomultiplier tubes) to detect light signals generated in the xenon. However, these experiments are constantly evolving and increasing in size with each new phase: for example, the future detector of the XLZD collaboration will be a cylinder 3 m in diameter and 3 m high, operating with approximately 80 t of xenon. This opens the door for other types of photosensors to be more suitable under these conditions in contrast to the traditionally used tubes.

The new photomultiplier tube (PMT) model 12699-406-M4 manufactured by Hamamatsu has been characterized in a joint work with our collaborators from Nikhef (Amsterdam). This new photosensor is flatter compared to the previously used PMTs and mechanically more stable under these conditions. In this work, published in JINST, several 2" PMTs have been tested in liquid xenon under pressure and temperature conditions similar to those of existing experiments.

The XENON Collaboration has published a new paper in PRL, presenting the latest results of a search for weakly interacting massive particle (WIMP) dark matter using the XENONnT experiment, the latest-generation of multi-tonne scale xenon dual-phase time projection chamber operated by the collaboration at the INFN Laboratori Nazionali del Gran Sasso in Italy. The paper, "WIMP Dark Matter Search using a 3.1 Tonne-Year Exposure of the XENONnT Experiment" (PRL), reports on an analysis of data collected during the first two science runs of the experiment, corresponding to a total exposure of 3.1 tonne-years of the liquid xenon target.

The analysis is based on a blind search for nuclear recoil signals compatible with elastic WIMP scattering. No significant excess above the expected background was observed. The results therefore place new upper limits on the spin-independent WIMP–nucleon scattering cross section across a wide range of WIMP masses. Compared to previous XENONnT results, the sensitivity of the search is improved by approximately a factor of two, reflecting both the increased exposure and the strong control of backgrounds achieved by the experiment. These results further constrain the allowed parameter space for WIMP dark matter models and represent an important step in the ongoing program of direct dark matter searches. 

More information on the XENON project can be found at the XENON website.