51�������

Abstract:

LiquidO is an innovative radiation detector concept. The core idea is to exploit stochastic light confinement in a highly scattering medium to self-segment the detector volume. In this paper, we demonstrate event-by-event muon tracking in a LiquidO opaque scintillator detector prototype. The detector consists of a 30 mm cubic scintillator volume instrumented with 64 wavelength-shifting fibres arranged in an 8 × 8 grid with a 3.2 mm pitch and read out by silicon photomultipliers. A wax-based opaque scintillator with a scattering length of approximately 0.5 mm is used. The tracking performance of this LiquidO detector is characterised with cosmic-ray muons and the position resolution is demonstrated to be 450 μm per row of fibres. These results highlight the potential of LiquidO opaque scintillator detectors to achieve fine spatial resolution, enabling precise particle tracking and imaging.

Abstract:

This paper presents the first observation of top-quark pair production in association with two photons ( t t ¯ γ γ ). The measurement is performed in the single-lepton decay channel using proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider. The data correspond to an integrated luminosity of 140 fb − 1 recorded during Run 2 at a centre-of-mass energy of 13 TeV. The t t ¯ γ γ production cross section, measured in a fiducial phase space based on particle-level kinematic criteria for the lepton, photons, and jets, is found to be 2 . 42 − 0.53 + 0.58 fb , corresponding to an observed significance of 5.2 standard deviations. Additionally, the ratio of the production cross section of t t ¯ γ γ to top-quark pair production in association with one photon is determined, yielding ( 3 . 30 − 0.65 + 0.70 ) × 10 − 3 .

Abstract:

We have made improved measurements of three-flavor neutrino mixing with $19.7(16.3)\times {10}^{20}$ protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, as well as new proton and photon-tagged samples at the near detector. Significant improvements have been made to the flux and neutrino interaction modeling. T2K data continue to prefer the normal mass ordering and upper octant of ${\sin }^2{\theta }_{23}$ with a near-maximal value of the charge-parity violating phase with best-fit values in the normal ordering of ${\delta }_{\mathrm{CP}}=-{2.18}_{-0.47}^{+1.22}$ , ${\sin }^2{\theta }_{23}={0.559}_{-0.078}^{+0.018}$ and $\mathrm{\Delta }{m}_{32}^2=({+2.506}_{-0.052}^{+0.039})\times {10}^{-3}{\mathrm{eV}}^2$ .