Accelerator Neutrinos

Abstract:

A Galactic core-collapse supernova (CCSN) is likely to be observed in neutrino detectors around the world minutes to hours before the electromagnetic radiation arrives. The SNEWS2.0 network of neutrino and dark matter detectors aims to use the relative arrival times of the neutrinos at the different experiments to point back to the supernova so as to facilitate follow-up observation. One of the simplest methods to estimate the CCSN direction is to use the first neutrino events detected through the inverse beta decay (IBD) process, v̄_ep → e⁺n. We will consider neutrino detectors sensitive to IBD interactions with low backgrounds. The difference in signal arrival times between a large and a small detector will be biased, however, with the first event at the smaller detector, on average, arriving later than that at the larger detector. This bias can be mitigated by using these first events in a data-driven approach without recourse to simulations or models. The resulting method requires, at minimum, only the times of the first events at most detectors, along with a longer time series of events from one larger detector to act as a reference lightcurve. In this article, we demonstrate this method and its uncertainty estimate using pairs of detectors of different sizes and with different supernova distances. Finally, we use this method to calculate probability skymaps using four detectors currently in operation (Super-Kamiokande, JUNO, LVD, and SNO+) and show that the calculated probabilities yield appropriate confidence intervals for all supernova directions. The area of the 68\% confidence interval varies by distance and direction, but is expected to be a few thousand square degrees. The resulting skymaps should be useful for the multi-messenger community as a rapid, initial pointing to follow up on the SNEWS2.0 Galactic CCSN neutrino alert.

Abstract:

The Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment with a rich physics program that includes searches for the hypothetical phenomenon of proton decay. Utilizing liquid-argon time-projection chamber technology, DUNE is expected to achieve world-leading sensitivity in the proton decay channels that involve charged kaons in their final states. The first DUNE demonstrator, ProtoDUNE Single-Phase, was a 0.77 kt detector that operated from 2018 to 2020 at the CERN Neutrino Platform, exposed to a mixed hadron and electron test-beam with momenta ranging from 0.3 to $7\mathrm{GeV}/\mathrm{c}$ . We present a selection of low-energy kaons among the secondary particles produced in hadronic reactions, using data from the 6 and $7\mathrm{GeV}/\mathrm{c}$ beam runs. The selection efficiency is 1% and the sample purity 92%. The initial energies of the selected kaon candidates encompass the expected energy range of kaons originating from proton decay events in DUNE (below $\sim 200\mathrm{MeV}$ ). In addition, we demonstrate the capability of this detector technology to discriminate between kaons and other particles such as protons and muons, and provide a comprehensive description of their energy loss in liquid argon, which shows good agreement with the simulation. These results pave the way for future proton decay searches at DUNE.

Abstract:

A search for Standard Model Higgs bosons produced in association with a high-energy photon and decaying to b b ¯ is performed using 133 fb − 1 of s = 13 TeV pp collision data collected with the ATLAS detector at the Large Hadron Collider at CERN. The photon requirement reduces the multijet background, and the H → b b ¯ decay is the dominant decay mode. Event selection requirements target events produced by vector-boson fusion, the dominant production mode in this channel. Several improvements enhance the search sensitivity compared to previous measurements. These improvements include better background modelling and characterization, the use of a neural-network classifier, and an updated signal extraction strategy adopting a direct binned-likelihood fit to the classifier output. With these improvements, the Higgs boson signal strength is measured to be 0.2 ± 0.7 relative to the Standard Model prediction. This corresponds to an observed significance of 0.3 standard deviations, compared to an expectation of 1.5 standard deviations assuming the Standard Model.

Abstract:

A search for the Higgs boson decay to a Z boson and a photon in the ℓℓγ ( ℓ = e , μ ) final state is performed using pp collisions at s = 13.6 TeV recorded with the ATLAS detector at the Large Hadron Collider during 2022–2024, corresponding to an integrated luminosity of 165 fb − 1 . The signal yield, normalised to the Standard Model prediction, is measured to be μ = 0 . 9 − 0.6 + 0.7 , compatible with the expected value of μ = 1.0 ± 0.7 . This corresponds to an observed (expected) signal significance of 1.4 (1.5) standard deviations under the background-only hypothesis. This result is combined with that of a similar search performed with 140 fb − 1 of s = 13 TeV pp collisions to provide the best expected sensitivity to date to this rare decay, namely an observed (expected) signal strength of μ = 1 . 3 − 0.5 + 0.6 ( μ = 1 . 0 − 0.5 + 0.6 ), corresponding to an observed (expected) significance of 2.5 (1.9) standard deviations. The measurement is consistent with the Standard Model expectation.