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The detection of cosmic neutrinos with energies above a teraelectronvolt (TeV) offers a unique exploration into astrophysical phenomena 1 , 2 – 3 . Electrically neutral and interacting only by means of the weak interaction, neutrinos are not deflected by magnetic fields and are rarely absorbed by interstellar matter: their direction indicates that their cosmic origin might be from the farthest reaches of the Universe. High-energy neutrinos can be produced when ultra-relativistic cosmic-ray protons or nuclei interact with other matter or photons, and their observation could be a signature of these processes. Here we report an exceptionally high-energy event observed by KM3NeT, the deep-sea neutrino telescope in the Mediterranean Sea 4 , which we associate with a cosmic neutrino detection. We detect a muon with an estimated energy of 12 0 − 60 + 110 petaelectronvolts (PeV). In light of its enormous energy and near-horizontal direction, the muon most probably originated from the interaction of a neutrino of even higher energy in the vicinity of the detector. The cosmic neutrino energy spectrum measured up to now 5 , 6 – 7 falls steeply with energy. However, the energy of this event is much larger than that of any neutrino detected so far. This suggests that the neutrino may have originated in a different cosmic accelerator than the lower-energy neutrinos, or this may be the first detection of a cosmogenic neutrino 8 , resulting from the interactions of ultra-high-energy cosmic rays with background photons in the Universe. A very high-energy muon observed by the KM3NeT experiment in the Mediterranean Sea is evidence for the interaction of an exceptionally high-energy neutrino of cosmic origin.  

A bstract KM3NeT/ORCA is a water Cherenkov neutrino detector under construction and anchored at the bottom of the Mediterranean Sea. The detector is designed to study oscillations of atmospheric neutrinos and determine the neutrino mass ordering. This paper focuses on an initial configuration of ORCA, referred to as ORCA6, which comprises six out of the foreseen 115 detection units of photo-sensors. A high-purity neutrino sample was extracted, corresponding to an exposure of 433 kton-years. The sample of 5828 neutrino candidates is analysed following a binned log-likelihood method in the reconstructed energy and cosine of the zenith angle. The atmospheric oscillation parameters are measured to be sin 2 θ 23 = 0.51 − 0.05 + 0.04 , and Δ m 31 2 = 2.18 − 0.35 + 0.25 × 10 − 3 eV 2 ∪ − 2.25 − 1.76 × 10 − 3 eV 2 at 68% CL. The inverted neutrino mass ordering hypothesis is disfavoured with a p-value of 0.25.

A measurement of the atmospheric ν μ + ν ¯ μ flux with energies between 1 and 100 GeV is presented. The measurement has been performed using data taken with the first six detection units of the KM3NeT/ORCA detector, referred to as ORCA6. The data were collected between January 2020 and November 2021 and correspond to 510 days of livetime, with a total exposure of 433 kton · years. Using machine learning classification, 3894 neutrino candidate events have been selected with an atmospheric muon contamination of less than 1 % . The atmospheric ν μ + ν ¯ μ energy spectrum is derived using an unfolding procedure and the impact of systematic uncertainties is estimated. The atmospheric ν μ + ν ¯ μ flux measured using the ORCA6 configuration is in agreement with the values measured by other experiments.

A bstract In the era of precision measurements of neutrino oscillation parameters, it is necessary for experiments to disentangle discrepancies that may indicate physics beyond the Standard Model in the neutrino sector. KM3NeT/ORCA is a water Cherenkov neutrino detector under construction and anchored at the bottom of the Mediterranean Sea. The detector is designed to study the oscillations of atmospheric neutrinos and determine the neutrino mass ordering. This paper focuses on the initial configuration of ORCA, referred to as ORCA6, which comprises six out of the foreseen 115 detection units of photosensors. A high-purity neutrino sample was extracted during 2020 and 2021, corresponding to an exposure of 433 kton-years. This sample is analysed following a binned log-likelihood approach to search for invisible neutrino decay, in a three-flavour neutrino oscillation scenario, where the third neutrino mass state ν 3 decays into an invisible state, e.g. a sterile neutrino. The resulting best fit of the invisible neutrino decay parameter is α 3 = 0.92 − 0.57 + 1.08 × 10 − 4 eV 2 , corresponding to a scenario with θ 23 in the second octant and normal neutrino mass ordering. The results are consistent with the Standard Model, within a 2.1 σ interval.

The Cherenkov Telescope Array and the KM3NeT neutrino telescopes are major upcoming facilities in the fields of γ -ray and neutrino astronomy, respectively. Possible simultaneous production of γ rays and neutrinos in astrophysical accelerators of cosmic-ray nuclei motivates a combination of their data. We assess the potential of a combined analysis of CTA and KM3NeT data to determine the contribution of hadronic emission processes in known Galactic γ -ray emitters, comparing this result to the cases of two separate analyses. In doing so, we demonstrate the capability of Gammapy , an open-source software package for the analysis of γ -ray data, to also process data from neutrino telescopes. For a selection of prototypical γ -ray sources within our Galaxy, we obtain models for primary proton and electron spectra in the hadronic and leptonic emission scenario, respectively, by fitting published γ -ray spectra. Using these models and instrument response functions for both detectors, we employ the Gammapy package to generate pseudo data sets, where we assume 200 h of CTA observations and 10 years of KM3NeT detector operation. We then apply a three-dimensional binned likelihood analysis to these data sets, separately for each instrument and jointly for both. We find that the largest benefit of the combined analysis lies in the possibility of a consistent modelling of the γ -ray and neutrino emission. Assuming a purely leptonic scenario as input, we obtain, for the most favourable source, an average expected 68% credible interval that constrains the contribution of hadronic processes to the observed γ -ray emission to below 15%.

A measurement of the atmospheric$$\\nu _{\\mu }+\\bar{\\nu }_{\\mu }$$ν μ + ν ¯ μ flux with energies between 1 and 100 GeV is presented. The measurement has been performed using data taken with the first six detection units of the KM3NeT/ORCA detector, referred to as ORCA6. The data were collected between January 2020 and November 2021 and correspond to 510 days of livetime, with a total exposure of 433 kton$$\\cdot $$· years. Using machine learning classification, 3894 neutrino candidate events have been selected with an atmospheric muon contamination of less than 1$$\\%$$% . The atmospheric$$\\nu _{\\mu }+\\bar{\\nu }_{\\mu }$$ν μ + ν ¯ μ energy spectrum is derived using an unfolding procedure and the impact of systematic uncertainties is estimated. The atmospheric$$\\nu _{\\mu }+\\bar{\\nu }_{\\mu }$$ν μ + ν ¯ μ flux measured using the ORCA6 configuration is in agreement with the values measured by other experiments.

Lorentz invariance is a fundamental symmetry of spacetime and foundational to modern physics. One of its most important consequences is the constancy of the speed of light. This invariance, together with the geometry of spacetime, implies that no particle can move faster than the speed of light. In this article, we present the most stringent neutrino-based test of this prediction, using the highest-energy neutrino ever detected to date, KM3-230213A. If we assume an extragalactic source as the origin, the arrival of this event, with an energy of 22 0 − 110 + 570 PeV , sets a constraint on δ ≡ c ν 2 − 1 < 4 . 2 − 3.7 + 9.2 × 1 0 − 22 . The potential for neutrinos to travel faster than light challenges fundamental physics, yet remains unconfirmed. The authors utilize the KM3NeT neutrino telescope to impose stringent constraints on Lorentz-violating superluminal neutrino velocities, reinforcing the standard understanding of Lorentz symmetry and impacting future theoretical and experimental explorations in particle physics.

Electrically charged particles can be created by the decay of strong enough electric fields, a phenomenon known as the Schwinger mechanism 1 . By electromagnetic duality, a sufficiently strong magnetic field would similarly produce magnetic monopoles, if they exist 2 . Magnetic monopoles are hypothetical fundamental particles that are predicted by several theories beyond the standard model 3 – 7 but have never been experimentally detected. Searching for the existence of magnetic monopoles via the Schwinger mechanism has not yet been attempted, but it is advantageous, owing to the possibility of calculating its rate through semi-classical techniques without perturbation theory, as well as that the production of the magnetic monopoles should be enhanced by their finite size 8 , 9 and strong coupling to photons 2 , 10 . Here we present a search for magnetic monopole production by the Schwinger mechanism in Pb–Pb heavy ion collisions at the Large Hadron Collider, producing the strongest known magnetic fields in the current Universe 11 . It was conducted by the MoEDAL experiment, whose trapping detectors were exposed to 0.235 per nanobarn, or approximately 1.8 × 10 9 , of Pb–Pb collisions with 5.02-teraelectronvolt center-of-mass energy per collision in November 2018. A superconducting quantum interference device (SQUID) magnetometer scanned the trapping detectors of MoEDAL for the presence of magnetic charge, which would induce a persistent current in the SQUID. Magnetic monopoles with integer Dirac charges of 1, 2 and 3 and masses up to 75 gigaelectronvolts per speed of light squared were excluded by the analysis at the 95% confidence level. This provides a lower mass limit for finite-size magnetic monopoles from a collider search and greatly extends previous mass bounds. At the Large Hadron Collider, the MoEDAL experiment shows no evidence for magnetic monopoles generated via the Schwinger mechanism at integer Dirac charges below 3, and suggests a lower mass limit of 75 GeV/ c 2 .

A bstract The MoEDAL experiment is designed to search for magnetic monopoles and other highly-ionising particles produced in high-energy collisions at the LHC. The largely passive MoEDAL detector, deployed at Interaction Point 8 on the LHC ring, relies on two dedicated direct detection techniques. The first technique is based on stacks of nucleartrack detectors with surface area ~18m 2 , sensitive to particle ionisation exceeding a high threshold. These detectors are analysed offline by optical scanning microscopes. The second technique is based on the trapping of charged particles in an array of roughly 800 kg of aluminium samples. These samples are monitored offline for the presence of trapped magnetic charge at a remote superconducting magnetometer facility. We present here the results of a search for magnetic monopoles using a 160 kg prototype MoEDAL trapping detector exposed to 8TeV proton-proton collisions at the LHC, for an integrated luminosity of 0.75 fb –1 . No magnetic charge exceeding 0:5 g D (where g D is the Dirac magnetic charge) is measured in any of the exposed samples, allowing limits to be placed on monopole production in the mass range 100 GeV≤ m ≤ 3500 GeV. Model-independent cross-section limits are presented in fiducial regions of monopole energy and direction for 1 g D  ≤ | g | ≤ 6 g D , and model-dependent cross-section limits are obtained for Drell-Yan pair production of spin-1/2 and spin-0 monopoles for 1 g D  ≤ | g | ≤ 4 g D . Under the assumption of Drell-Yan cross sections, mass limits are derived for | g | = 2 g D and | g | = 3 g D for the first time at the LHC, surpassing the results from previous collider experiments.