News

Figures from the GERDA paper  "Searches for new physics below twice the electron mass with GERDA" were featured on the cover of September's issue of the EPJ-C journal.   The paper, containing significant contributions by our group's former PhD student Yannick Müller, describes the search for full-energy depositions from bosonic keV-scale dark matter candidates of masses between 65 and 1021 keV using data from 105.5 kg-years of GERDA's Phase II exposure.

In the same EPJ-C issue, the first paper from MONUMENT was published, describing MONUMENT's experimental setup, utilized to measure ordinary muon capture (OMC) on isotopes relevant to neutrinoless double-beta decay. The paper also features data of OMC on ⁷⁶Se and ¹³⁶Ba, the isotopes critical for searches with the next-generation experiments like LEGEND and nEXO, using  ⁷⁶Ge and ¹³⁶Xe targets. The analysis and identification of lines in the ¹³⁶Ba data, highlighted in the paper, were part of the PhD work of our group member  Gabriela Araujo.

"What if a mineral could reveal what it’s seen over the millions—or billions—of years it’s been sitting deep within Earth? An interdisciplinary global network of scientists is reviving efforts to unlock the secrets that minerals hold."

In this article, Physics Today journalist Toni Feder describes the efforts of a U.S.-European multi-institutional initiative, including our group, to detect dark matter and learn more about neutrinos. The article details our work on imaging color centers in transparent crystals using the state-of-the-art microscope mesoSPIM.

This work is the focus of the UZH Postdoc grant awarded to our group member Gabriela Araujo and is performed in close collaboration with mesoSPIM developer Dr. Nikita Vladimirov from the URPP Adaptive Brain Circuits in Development and Learning department, and Prof. Patrick Huber from Virginia Tech. Key measurements described in the article, such as fluorescent tracks induced by alpha particles and neutrons in transparent crystals, were recently presented by Araujo on behalf of the PALEOCCENE team at the Applied Antineutrino Physics Workshop 2024, and will soon be published in an upcoming paper.

Several members of our group organized and participated in the outreach activity Physics on Tap.  In the relaxed setting of a bar, physics enthusiasts had the opportunity to engage in one-on-one conversations with UZH physicists.

The activity gathered over 40 attendees and featured talks by Dr. Ricardo Peres and Marko Persut, a Speed-Meeting a Physicist session moderated by Dr. Gabriela Araujo, and a pub quiz moderated by Nicolo Geraudo. The quiz was won by the Black Hole Sun team, comprising young physicists from our group - Aravind Remesansreekala, Sana Ouahada, and Alain Fauquex - who partnered with physics enthusiasts to take home the prize. Our group members Paloma Cimental, Gloria Senatore, and Dr. Jose C. Garcia additionally showcased their research to other attendees during the  Speed-Meeting a Physicist session.

The first measurement of solar ⁸B neutrinos via coherent elastic neutrino-nucleus scattering (CEνNS) in XENONnT has been published in Physical Review Letters.

The CEνNS process was measured for the first time with neutrinos from a natural source at a significance of 2.73σ. Results from the PandaX-4T experiment were published alongside. This marks the first glimpse of the so-called neutrino fog: As neutrinos interact in the same way as weakly interacting massive dark matter particles (WIMPs), the respective signals in a detector are indistinguishable.

Neutrinos are weakly interacting particles within the Standard Model of particle physics. At energies of few to tens of megaelectronvolts they predominantly interact coherently with an entire atomic nucleus rather than with individual protons, neutrons or atomic electrons. Such neutrinos are abundant in Earth’s cosmic neighborhood, as they are emitted from the sun, are produced by cosmic ray bombardment of the atmosphere and remain as a diffuse background from supernovae throughout the history of the Milky Way. These three components constitute the neutrino fog for dark matter detection in which neutrinos might hide dark matter signals.

While solar neutrinos have lower energies than the other two components, their larger particle flux impinging on Earth makes them the first component to be detectable in experiments. However, a detection required lowering the energy threshold of XENONnT, as even the highest energy solar ⁸B neutrinos only deposit few kiloelectronvolts of energy inside the detector. While a lower threshold could be achieved by allowing signals for analysis that were seen by fewer sensors inside the detector, this meant a large increase in unphysical background events. In order to reject such background events, the data analysis relied heavily on machine learning. This allowed to determine that out of 37 measured events, 26 events would originate from background while 11 events were attributed to CEνNS.

A lot of WIMP parameter space can still be probed before the atmospheric and diffuse supernova components start to pose a challenge for experiments. With future data, XENONnT and the upcoming DARWIN/XLZD experiment will venture down into the fog.

During the IDM conference in L'Aquila, Italy, the XENON collaboration announced the detection of signals produced by neutrinos coming from the Sun. These neutrinos can interact with xenon nuclei via the so-called CEvNS (coherent elastic neutrino-nucleus scattering), and thanks to the ultra-low background environment and the low-energy detection capability of XENONnT, this detection was possible.

The outcome of this analysis shows events that are compatible with signals of the scattering of solar B-8 neutrinos with xenon nuclei within a statistical uncertainty of 2.7 sigma. This means that the probability of these signals being background is around 0.35%.

Although CEvNS had already been observed before in another experiment (COHERENT, 2017), this is the first time that an experiment detects CEvNS of neutrinos from the Sun.

For more info, visit the XENON web page

Local information: The group of Prof. Laura Baudis at the University of Zurich had major responsibilities in the XENONnT TPC design and assembly, in the installation, calibration and readout electronics of the 494 photosensors, and in the measurements of tiny radioactivity traces in detector materials. The group also has leading involvements in the data analysis and in Monte Carlo simulations of the expected TPC signals and backgrounds.