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A bstract The electron (anti-)neutrino component of the T2K neutrino beam constitutes the largest background in the measurement of electron (anti-)neutrino appearance at the far detector. The electron neutrino scattering is measured directly with the T2K off-axis near detector, ND280. The selection of the electron (anti-)neutrino events in the plastic scintillator target from both neutrino and anti-neutrino mode beams is discussed in this paper. The flux integrated single differential charged-current inclusive electron (anti-)neutrino cross-sections, dσ/dp and dσ/d cos( θ ), and the total cross-sections in a limited phase-space in momentum and scattering angle ( p > 300 MeV/c and θ ≤ 45°) are measured using a binned maximum likelihood fit and compared to the neutrino Monte Carlo generator predictions, resulting in good agreement.

A bstract This article describes BabyIAXO, an intermediate experimental stage of the International Axion Observatory (IAXO), proposed to be sited at DESY. IAXO is a large-scale axion helioscope that will look for axions and axion-like particles (ALPs), produced in the Sun, with unprecedented sensitivity. BabyIAXO is conceived to test all IAXO subsystems (magnet, optics and detectors) at a relevant scale for the final system and thus serve as prototype for IAXO, but at the same time as a fully-fledged helioscope with relevant physics reach itself, and with potential for discovery. The BabyIAXO magnet will feature two 10 m long, 70 cm diameter bores, and will host two detection lines (optics and detector) of dimensions similar to the final ones foreseen for IAXO. BabyIAXO will detect or reject solar axions or ALPs with axion-photon couplings down to g aγ ∼ 1 . 5 × 10 − 11 GeV − 1 , and masses up to m a ∼ 0 . 25 eV. BabyIAXO will offer additional opportunities for axion research in view of IAXO, like the development of precision x-ray detectors to identify particular spectral features in the solar axion spectrum, and the implementation of radiofrequency-cavity-based axion dark matter setups.

A bstract The MicroBooNE liquid argon time projection chamber located at Fermilab is a neutrino experiment dedicated to the study of short-baseline oscillations, the measurements of neutrino cross sections in liquid argon, and to the research and development of this novel detector technology. Accurate and precise measurements of calorimetry are essential to the event reconstruction and are achieved by leveraging the TPC to measure deposited energy per unit length along the particle trajectory, with mm resolution. We describe the non-uniform calorimetric reconstruction performance in the detector, showing dependence on the angle of the particle trajectory. Such non-uniform reconstruction directly affects the performance of the particle identification algorithms which infer particle type from calorimetric measurements. This work presents a new particle identification method which accounts for and effectively addresses such non-uniformity. The newly developed method shows improved performance compared to previous algorithms, illustrated by a 93.7% proton selection efficiency and a 10% muon mis-identification rate, with a fairly loose selection of tracks performed on beam data. The performance is further demonstrated by identifying exclusive final states in ν μ CC interactions. While developed using MicroBooNE data and simulation, this method is easily applicable to future LArTPC experiments, such as SBND, ICARUS, and DUNE.

A measurement of the ${K}^{+}\\to {\\pi}^{+}\\nu \\overline{\\nu}$ decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This dataset was recorded, after modifications to the beamline and detectors, at a higher instantaneous beam intensity with respect to the 2016–2018 data taking. Combining NA62 data collected in 2016–2022, a measurement $\\mathcal{B} ({K}^{+}\\to {\\pi}^{+}\\nu \\overline{\\nu}) = \\large{(}13.0^{+3.3}_{-3.0}\\large{)}$ x $10^{-11}$ of is reported. With 51 signal candidates observed and an expected background of $18^{+3}_{-2}$ events, $\\mathcal{B} ({K}^{+}\\to {\\pi}^{+}\\nu \\overline{\\nu})$ becomes the smallest branching ratio measured with a signal significance above 5σ.

A bstract We present a unified theoretical framework for computing spin-independent direct detection rates via various channels relevant for sub-GeV dark matter — nuclear re- coils, electron transitions and single phonon excitations. Despite the very different physics involved, in each case the rate factorizes into the particle-level matrix element squared, and an integral over a target material- and channel-specific dynamic structure factor. We show how the dynamic structure factor can be derived in all three cases following the same procedure, and extend previous results in the literature in several aspects. For electron transitions, we incorporate directional dependence and point out anisotropic target materials with strong daily modulation in the scattering rate. For single phonon excitations, we present a new derivation of the rate formula from first principles for generic spin-independent couplings, and include the first calculation of phonon excitation through electron couplings. We also discuss the interplay between single phonon excitations and nuclear recoils, and clarify the role of Umklapp processes, which can dominate the single phonon production rate for dark matter heavier than an MeV. Our results highlight the complementarity between various search channels in probing different kinematic regimes of dark matter scattering, and provide a common reference to connect dark matter theories with ongoing and future direct detection experiments.

A bstract A measurement of the K + → π + ν ν ¯ decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This dataset was recorded, after modifications to the beamline and detectors, at a higher instantaneous beam intensity with respect to the 2016–2018 data taking. Combining NA62 data collected in 2016–2022, a measurement of B K + → π + ν ν ¯ = 13.0 − 3.0 + 3.3 × 10 − 11 is reported. With 51 signal candidates observed and an expected background of 18 − 2 + 3 events, B K + → π + ν ν ¯ becomes the smallest branching ratio measured with a signal significance above 5 σ .

A bstract In this paper we study CP violation in photon self-interactions at low energy. These interactions, mediated by the effective operator FFF F ˜ , where ( F ˜ ) F is the (dual) electromagnetic field strength, have yet to be directly probed experimentally. Possible sources for such interactions are weakly coupled light scalars with both scalar and pseudoscalar couplings to photons (for instance, complex Higgs-portal scalars or the relaxion), or new light fermions coupled to photons via dipole operators. We propose a method to isolate the CP-violating contribution to the photon self-interactions using Superconducting Radio-Frequency cavities and vacuum birefringence experiments. In addition, we consider several theoretical and experimental indirect bounds on the scale of new physics associated with the above effective operator, and present projections for the sensitivity of the proposed experiments to this scale. We also discuss the implications of these bounds on the CP-violating couplings of new light particles coupled to photons.

A bstract We propose an experimental setup to search for Axion-like particles (ALPs) using two superconducting radio-frequency cavities. In this light-shining-through-wall setup the axion is sourced by two modes with large fields and nonzero E → ⋅ B → in an emitter cavity. In a nearby identical cavity only one of these modes, the spectator, is populated while the other is a quiet signal mode. Axions can up-convert off the spectator mode into signal photons. We discuss the physics reach of this setup finding potential to explore new ALP parameter space. Enhanced sensitivity can be achieved if high-level modes can be used, thanks to improved phase matching between the excited modes and the generated axion field. We also discuss the potential leakage noise effects and their mitigation, which is aided by O (GHz) separation between the spectator and signal frequencies.

Abstract A measurement of the K + → π + ν ν ¯$$ {K}^{+}\\to {\\pi}^{+}\\nu \\overline{\\nu} $$decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This dataset was recorded, after modifications to the beamline and detectors, at a higher instantaneous beam intensity with respect to the 2016–2018 data taking. Combining NA62 data collected in 2016–2022, a measurement of B K + → π + ν ν ¯ = 13.0 − 3.0 + 3.3 × 10 − 11$$ \\mathcal{B}\\left({K}^{+}\\to {\\pi}^{+}\\nu \\overline{\\nu}\\right)=\\left({13.0}_{-3.0}^{+3.3}\\right)\\times {10}^{-11} $$is reported. With 51 signal candidates observed and an expected background of 18 − 2 + 3$$ {18}_{-2}^{+3} $$events, B K + → π + ν ν ¯$$ \\mathcal{B}\\left({K}^{+}\\to {\\pi}^{+}\\nu \\overline{\\nu}\\right) $$becomes the smallest branching ratio measured with a signal significance above 5σ.

A bstract Fermion dark matter particles can aggregate to form extended dark matter structures via a first-order phase transition in which the particles get trapped in the false vacuum. We study Fermi balls created in a phase transition induced by a generic quartic thermal effective potential. We show that for Fermi balls of mass, 3 × 10 − 12 M ⊙ ≲ M FB ≲ 10 − 5 M ⊙ , correlated observations of gravitational waves produced during the phase transition (at SKA/THEIA/ μ Ares), and gravitational microlensing caused by Fermi balls (at Subaru-HSC), can be made.