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The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed by Hamamatsu for dark matter direct detection experiments using liquid xenon as the target material. We present the results from the joint effort between the XENON collaboration and the Hamamatsu company to produce a highly radio-pure photosensor (version R11410-21) for the XENON1T dark matter experiment. After introducing the photosensor and its components, we show the methods and results of the radioactive contamination measurements of the individual materials employed in the photomultiplier production. We then discuss the adopted strategies to reduce the radioactivity of the various PMT versions. Finally, we detail the results from screening 286 tubes with ultra-low background germanium detectors, as well as their implications for the expected electronic and nuclear recoil background of the XENON1T experiment.

Laboratory experiments searching for galactic dark matter particles scattering off nuclei have so far not been able to establish a discovery. We use data from the XENON100 experiment to search for dark matter interacting with electrons. With no evidence for a signal above the low background of our experiment, we exclude a variety of representative dark matter models that would induce electronic recoils. For axial-vector couplings to electrons, we exclude cross sections above 6 × 10–35 cm2 for particle masses of mx = 2 GeV/c2. Independent of the dark matter halo, we exclude leptophilic models as an explanation for the long-standing DAMA/LIBRA signal, such as couplings to electrons through axial-vector interactions at a 4.4σ. confidence level, mirror dark matter at 3.6σ, and luminous dark matter at 4.6σ.

Since 2019, the Extreme Energy Events (EEE) Project has installed three muon detection stations at the Svalbard Islands ( 78 . 9 ∘ N latitude), employing scintillator-based detectors. This initiative represents the first systematic effort to monitor cosmic-muons rates at high geomagnetic latitudes beyond the Arctic Circle, with the objective of improving our understanding of cosmic-ray propagation and modulation in polar regions. The present study analyses temporal variations in the muon detection rates over a six-year period (2019–2025), including the study of periodic modulations and underlying trends in the observed rates.

The selection of low-radioactive construction materials is of utmost importance for the success of low-energy rare event search experiments. Besides radioactive contaminants in the bulk, the emanation of radioactive radon atoms from material surfaces attains increasing relevance in the effort to further reduce the background of such experiments. In this work, we present the 222Rn emanation measurements performed for the XENON1T dark matter experiment. Together with the bulk impurity screening campaign, the results enabled us to select the radio-purest construction materials, targeting a 222Rn activity concentration of 10μBq/kg in 3.2t of xenon. The knowledge of the distribution of the 222Rn sources allowed us to selectively eliminate problematic components in the course of the experiment. The predictions from the emanation measurements were compared to data of the 222Rn activity concentration in XENON1T. The final 222Rn activity concentration of (4.5±0.1)μBq/kg in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.

After its successful campaign of measurements beyond the Polar Arctic Circle, the PolarquEEEst experiment measured the cosmic charged particle rate at sea level in a latitude interval between 35 ∘ N and 82 ∘ N. In this paper, these measurements are described and the corresponding results are discussed.

The eruption of the Hunga-Tonga volcano in the South Pacific Ocean on January 15, 2022, at about 4:15 UTC, generated a violent explosion, which created atmospheric pressure disturbances in the form of Rayleigh-Lamb waves detected all over the globe. Here we discuss the observation of the Hunga-Tonga shock-wave performed at the Ny-Ålesund Research Station on the Spitsbergen island, by the detectors of the PolarquEEEst experiment and their ancillary sensors. Online pressure data as well as the results of dedicated offline analysis are presented and discussed in details. Results include wave arrival times, wave amplitude measurements and wave velocity calculation. We observed five passages of the shock wave with a significance larger than 3 σ and an amplitude up to 1 hPa. The average propagation velocity resulted to be (308 ± 0.6) m/s. Possible effects of the atmospheric pressure variation associated with the shock-wave multiple passages on the cosmic-ray rate at ground level are also investigated. We did not find any significant evidence of this effect.

After its successful campaign of measurements beyond the Polar Arctic Circle, the PolarquEEEst experiment measured the cosmic charged particle rate at sea level in a latitude interval between 35$$^{\\circ }$$∘ N and 82$$^{\\circ }$$∘ N. In this paper, these measurements are described and the corresponding results are discussed.

Since 2019, three scintillator-based cosmic ray detectors, readout by SiPM and controlled by low-cost electronics, are installed in the scientific research site in Ny Ålesund (Svalbard) at 79°N, recording muons from secondary cosmic rays. The detectors are part of the EEE Project, a joint project of Centrofermi and INFN, involving almost 100 secondary schools in Italy. After collecting nearly 5 years of data, we were able to analyse the muon rate time series and observe an evident oscillating component with a period of about one year. Applying the Lomb-Scargle periodogram technique, based on sinusoidal fit optimization, we could quantify the annual component, after verifying its independence from environmental and experimental factors.

The Extreme Energy Events Project is an educational and scientific initiative lead by the Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi (CREF) and the Istituto Nazionale di Fisica Nucleare (INFN), two research Institutions under the control of the Italian Ministero dell’Universit`a e Ricerca (MUR). The EEE Project studies cosmic rays by means of a series of detectors located inside Italian high schools or INFN/University laboratories. The detectors have been built and are operated with the strong cooperation of students and teachers. Data from the different EEE detectors are centrally collected, reconstructed, and analyzed for scientific publications. However, they are also distributed to the students, who actively participate in the study of the properties of the muon flux and present their work at general meetings organized both online or in-person. It is important to underline that the Project involves the student during an entire year (and sometimes even more) allowing a continuous interaction with the researchers involved. A description of the outreach activities and of their impact on the students’ learning curve will be provided, together with a few examples of activities that led to students-signed publications.

The goal of the PolarquEEEst experiment was to measure the cosmic charged particle rate at latitudes greater than 66 ∘ N, where no systematic and accurate measurements at sea level have ever been performed. A latitude range well above the Arctic Circle was explored on board of a sailboat, up to the unprecedented northernmost value of 82 ∘ 07 ′ N. In this paper a description of the experimental set-up is reported, then the procedures for calibration and data analysis are described in detail. The results show that the rate measured in this latitude range stays constant within a novel accuracy of ± 1 %.