In the simple two-generation case, the probability P_{\mu \tau}Pμτ is not affected by interactions of neutrinos in matter. But for three-generation case, at baselines of the order of 9000 km, matter effects become important for this channel. This is a genuine three-flavour effect. We study how the presence of non-standard interactions (NSI) alters the P_{\mu \tau}Pμτ at these baselines. We observe large deviations from the standard matter effect. In particular, we find energies and baselines for which the phases governing the NSIs do not play any role. This may facilitate a better determination of NSI parameters if tau neutrinos can be detected.

Hyper-Kamiokande is the next-generation neutrino observatory, aiming to tackle a broad spectrum of physics programs. These include probing leptonic CP violation through long baseline accelerator neutrino oscillations, determining neutrino mass ordering, potentially discovering the proton decay, and capturing neutrinos from supernova relics, other astrophysical sources, and the sun. As the world’s largest underground Cherenkov detector, Hyper-Kamiokande boasts a fiducial volume eight times that of its predecessor, Super-Kamiokande. With 258 kton of ultrapure water as its medium, Hyper-Kamiokande is scheduled to begin its groundbreaking operations in 2027, located in Kamioka, Japan. This proceeding outlines the ambitious physics program of Hyper-Kamiokande, details of the design of the detector, and provides an update on its current status.

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment currently under construction in China. It is located 52.5 km away from two nuclear power plants in a newly constructed 700-m-deep underground laboratory. JUNO will be the largest liquid scintillator (LS) detector in the world comprising 20 kt of ultra-pure LS filled in an acrylic sphere. Its main goal is to determine the neutrino mass ordering by measuring the energy spectrum of reactor neutrinos with highest accuracy. In addition, JUNO will cover precision measurements of oscillation parameters and several aspects in the field of astroparticle physics. Data taking will start in late 2024.

One of the purposes of High Energy accelerator experiments is confrontation of theory and measurements in ever new realms. Any new agreement extends theory applicability domain, any discrepancy hints to unexplained, calling for better calculations or new, deeper theory. Often one has to search for small contributions over large Standard Model background. Multidimensional signatures and complex background subtraction cuts imply that Monte Carlo techniques are indispensable. My talk included description of: KKMC Monte Carlo for e^+e^- \to \tau^+\tau^- (n\gamma)e+e−→τ+τ−(nγ) (with \tauτ decays), generation of additional lepton pairs of SM and New Physics, and contributions from anomalous magnetic and electric dipole moments.

Lepton flavor violating processes are highly suppressed in the Standard Model. Therefore, if observed, lepton flavor violation would be a clear indication of new physics beyond the Standard Model. We study the process e^+e^-\to\tau\mue+e−→τμ at tree-level in the Standard Model Effective Field Theory both on the ZZ-pole and at higher center-of-mass energies. We show that the constraints derived from the future circular e^+e^-e+e− colliders FCC-ee and CEPC, are complementary to those obtained from low-energy tau decays at BaBar and Belle, as well as projections from Belle-II.

Three analyses exploiting the H→\tau\tauH→ττ process using 139 fb^{-1}−1 of proton–proton collision data collected at a center-of-mass energy of 13 TeV by the ATLAS detector at the LHC are presented. A measurement of VHVH production, with V(=W, Z)→ e\nu/\mu\nu,ee/\mu\muV(=W,Z)→eν/μν,ee/μμ decays, has established the first evidence for this process with an observed (expected) significance of 4.2 (3.6) standard deviations. The second analysis, first of its kind by the ATLAS collaboration, probes CP-invariance if the decay products of the \tauτ leptons using an angular observable \phi_\tauϕτ, and measured an observed (expected) value of \phi_\tau=9 ± 16^\circ (0 ± 28^\circ)ϕτ=9±16∘(0±28∘) at 68% confidence level. The last analysis is a search for lepton-flavour-violation in H→ e\tau/\mu\tauH→eτ/μτ decays, where most stringent exclusion limits at 95% confidence level on H→ e\tauH→eτ branching ratio of 0.2%, is obtained.

Recent R&D work associated with upgrading the SuperKEKB e^+e^-e+e− collider with polarized electron beams is presented. The Chiral Belle physics program enables a set of unique precision measurements using the Belle II detector. It includes a set of measurements of \sin^2\theta_Wsin2θW via separate left-right asymmetry (A_{LR}ALR) measurements in annihilations to pairs of electrons, muons, taus, charm and b-quarks that yield precisions matching or exceeding those of the current world averages from measurements at the Z^0Z0-pole, but at 10GeV, thereby also probing the running of the couplings. Chiral Belle will also probe for new physics via the highest precision measurements of neutral current universality ratios and precision measurements of tau lepton properties, including the tau magnetic moment. After summarizing the physics goals, developments related to provision of the polarized source, the new components of the accelerator lattice that rotate the electron spin from transverse to longitudinal at the interaction point, and polarimetry of the electron beam will be reported.

TAMBO is a planned next-generation neutrino observatory sensitive to 1-100 PeV Earth-skimming tau neutrinos. This tau neutrino specificity will provide a high-purity sample of astrophysical neutrinos whose locations on the sky can then be used to improve the sensitivities of all-flavor neutrino observatories. The observatory will be located in a deep canyon and will comprise an array of water-Cherenkov and plastic scintillator air-shower detectors. In this proceeding, I will summarize the current status of the updated TAMBO simulation package, which is currently being used for detector optimization and reconstruction studies.

In the Standard Model (SM) lepton flavour numbers are approximately conserved at energies accessible to current experiments, where lepton flavour violation is extremely suppressed. The observation of neutrino oscillations, however, proves that neutrinos are massive particles and allows for additional Lepton Flavour Violating (LFV) processes also at low energies. Nevertheless, these processes are predicted with very low branching ratios and are sensitive to new physics effects, which could manifest as an enhancement in the decay probability. Similarly, Lepton Flavour Universality Violating (LFUV) observables allows for the test of the SM and the study of beyond the SM theories. The latest CMS results from the Higgs, B-physics and exotica groups are presented on the search for LFV and LFUV with tau leptons in the final state. The results are based on data collected in proton-proton collisions at the centre-of-mass energy of 13 TeV.

We review the \tauτ data-driven computation of Euclidean windows for the hadronic vacuum polarization contribution to the muon anomalous magnetic moment (a_\muaμ), which agree with the lattice results, making the difference of the e^+e^-e+e− data-driven methods with them more intriguing. This conundrum needs to be solved by next year, when the final FNAL a_\muaμ measurement will be published, in order to extract firm conclusions on possible new physics effects.