Dual-phase xenon time projection chambers for rare-event searches

In the past decade, dual-phase xenon time projection chambers (Xe-TPCs) have emerged as some of the most powerful detectors in the fields of astroparticle physics and rare-event searches. Developed primarily towards the direct detection of dark matter particles, experiments presently operating deep underground have reached target masses at the multi-tonne scale, energy thresholds of approximately 1 keV and radioactivity-induced background rates similar to those from solar neutrinos. These unique properties, together with demonstrated stable operation over several years, allow for the exploration of new territory via high-sensitivity searches for a plethora of ultra-rare interactions. These include searches for particle dark matter, for second-order weak decays, and the observation of astrophysical neutrinos. We first review some properties of xenon as a radiation detection medium and the operation principles of dual-phase Xe-TPCs together with their energy calibration and resolution. We then discuss the status of currently running experiments and of proposed next-generation projects, describing some of the technological challenges. We end by looking at their sensitivity to dark matter candidates, to second-order weak decays and to solar and supernova neutrinos. Experiments based on dual-phase Xe-TPCs are difficult and, like all good experiments, they are constantly pushed to their limits. Together with many other endeavours in astroparticle physics and cosmology they will continue to push at the borders of the unknown, hopefully to reveal profound new knowledge about our cosmos. This article is part of the theme issue 'The particle-gravity frontier'.

GRB 221009A Gamma Rays from the Radiative Decay of Heavy Neutrinos?

We consider a mechanism that causes a decrease in the attenuation of high energy gamma-ray flux from gamma ray burst GRB 221009A. The mechanism is based on the existence of a heavy m_{N}∼(0.1-1)  MeV mostly sterile neutrino N which mixes with active neutrinos. N's are produced in the gamma-ray burst (GRB) in π and K decays via mixing with ν_{μ}. They undergo the radiative decay N→νγ on the way to Earth. The usual exponential attenuation of gamma rays is lifted to an attenuation inverse in the optical depth. Various restrictions on this scenario are discussed. We find that the high energy γ events at 18 TeV can be explained if (i) the GRB active neutrino fluence is close to the observed limit, (ii) the branching ratio of N→νγ is at least of the order 10%.

Diffuse neutrino background from past core collapse supernovae

Core collapse supernovae are among the most powerful explosions in the Universe, which emit thermal neutrinos that carry away most of the gravitational binding energy released. These neutrinos produce a diffuse supernova neutrino background (DSNB), which is one of the largest energy budgets among all radiation backgrounds. Detecting the DSNB is an important goal of modern high-energy astrophysics and particle physics, which provides valuable insights into core collapse modeling, neutrino physics, and cosmic supernova rate history. In this review, the key ingredients of DSNB calculation and what can be learned from future detections, including black hole formation and non-standard neutrino interactions are discussed. Moreover, an overview of the latest updates in neutrino experiments, which could lead to the detection of the DSNB in the next decade, is provided. With the promise of this breakthrough discovery on the horizon, the study of DSNB has great potential to further our understanding of the Universe.

Prospects for the Detection of the Diffuse Supernova Neutrino Background with the Experiments SK-Gd and JUNO

The advent of gadolinium-loaded Super-Kamiokande (SK-Gd) and of the soon-to-start JUNO liquid scintillator detector marks a substantial improvement in global sensitivity for the Diffuse Supernova Neutrino Background (DSNB). The present article reviews the detector properties most relevant for the DSNB searches in both experiments and estimates the expected signal and background levels. Based on these inputs, we evaluate the sensitivity of both experiments individually and combined. Using a simplified statistical approach, we find that both SK-Gd and JUNO have the potential to reach >3σ evidence of the DSNB signal within 10 years of measurement. Combination of their results is likely to enable a 5σ discovery of the DSNB signal within the next decade.