News

We congratulate our group member Dr. Marta Babicz for being awarded the prestigious UZH Postdoc Grant for early career researchers.

As part of the LEGEND collaboration, Marta will use this fellowship to pursue the search for signatures of neutrinoless double electron capture in 36-Ar with data from the LEGEND-200 experiment. This research contributes to the broader effort of probing the fundamental nature of neutrinos and testing lepton number violation.

Late June saw the collaboration meetings of the XENON and XLZD collaborations in L'Aquila and at Laboratori Nazionali del Gran Sasso (LNGS), respectively. Group members presented progress on XENONnT physics searches as well as hardware development for XLZD. While the XENONnT dark matter detector is hosted by LNGS, this marked the first general meeting of the XLZD collaboration in Italy. Collaborators had the chance to visit the underground laboratory which is one of the candidate sites for XLZD. The XLZD observatory is projected to be not only the ultimate xenon-based dark matter search experiment, but also a multi-purpose detector for a multitude of signals in astroparticle physics.

We are pleased to report the successful organization of the LEGEND  Pulse Shape Simulation Workshop hosted by our group at the University of Zurich.

The workshop brought together members of the LEGEND collaboration to discuss recent developments in simulating the pulse shape response in High Purity Ge detectors. Over three and a half  intensive days, participants exchanged ideas, coordinated efforts across projects, and planned future improvements to simulation tools and models for improving pulse shape discrimination and background modeling, both of which are critical for identifying rare neutrinoless double beta decay events in the LEGEND experiment. Accurate simulations enhance signal-to-background separation, guide detector design, and help optimise analysis methods, making them a vital part of our experimental strategy.

The workshop was made possible thanks to the GRC Short Grant, which supported the event's logistics. Its success reflects the value of focused, cross-collaboration meetings in advancing key aspects of our experimental program. Many thanks to all participants for their contributions and to the GRC for enabling this fruitful event!

Sofia Calgaro, a postdoctoral researcher from our group, had the opportunity to present the first and most recent LEGEND-200 results at the WIN 2025 conference in Brighton, UK (talk).
She presented both the Frequentist and Bayesian analyses of the 0νββ results based on the first year of collected data, which led to the most sensitive half-life limit for 0νββ decay to date. She also showed the first constraint on the effective Majorana neutrino mass (m_ββ), obtained using uncertainty-quantified nuclear matrix elements evaluated via ab initio methods for ⁷⁶Ge (paper).

The work was discussed in greater detail during the International School of Subnuclear Physics 2025 in Erice, Italy (talk). Participation in the school proved to be an invaluable opportunity to exchange ideas, deepen knowledge, and build new connections with a broaden community of researchers. As recognition for the results achieved and presented, Sofia was awarded the Giulio Racah diploma.

We are pleased to announce the publication of the paper XENONnT WIMP search: signal and background modeling and statistical inference in Physical Review D (link to publication).

While a first analysis paper described how raw data are processed into valid events for our WIMP dark matter search, this publication presents the following stage of the analysis, focusing on three core components: the detector response model based on calibration data, the development and validation of background and signal models, and the statistical framework used for inference, including likelihood construction and hypothesis testing.

Two postdoctoral researchers from our group, Diego and Luisa, are among the corresponding authors of this work and played key roles in the analysis. Congratulations to them for their contribution to the XENON experiment!