The T2K experiment observes indications of ${\nu }_{\mu }\to {\nu }_e$ appearance in data accumulated with $1.43\times {10}^{20}$ protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with $|\Delta m_{23}^2|=2.4\times {10}^{-3}{\mathrm{eV}}^2$, ${sin}^{2}2{\theta }_{23}=1$ and ${sin}^{2}2{\theta }_{13}=0$, the expected number of such events is $1.5\pm 0.3(\mathrm{syst})$. Under this hypothesis, the probability to observe six or more candidate events is $7\times {10}^{-3}$, equivalent to $2.5\sigma$ significance. At 90% C.L., the data are consistent with $0.03(0.04)<{sin}^{2}2{\theta }_{13}<0.28(0.34)$ for ${\delta }_{CP}=0$ and a normal (inverted) hierarchy.

The T2K experiment is a long baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle θ13θ13 by observing νeνe appearance in a νμνμ beam. It also aims to make a precision measurement of the known oscillation parameters, View the MathML sourceΔm232 and sin22θ23sin22θ23, via νμνμ disappearance studies. Other goals of the experiment include various neutrino cross-section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC. This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem

The ForwArd Search ExpeRiment (FASER) is an approved experiment dedicated to searching for light, extremely weakly interacting particles at the LHC. Such particles may be produced in the LHC’s high-energy collisions and travel long distances through concrete and rock without interacting. They may then decay to visible particles in FASER, which is placed 480 m downstream of the ATLAS interaction point. In this work we briefly describe the FASER detector layout and the status of potential backgrounds. We then present the sensitivity reach for FASER for a large number of long-lived particle models, updating previous results to a uniform set of detector assumptions, and analyzing new models. In particular, we consider all of the renormalizable portal interactions, leading to dark photons, dark Higgs bosons, and heavy neutral leptons; light $B-L$ and $L_i-L_j$ gauge bosons; axionlike particles that are coupled dominantly to photons, fermions, and gluons through nonrenormalizable operators; and pseudoscalars with Yukawa-like couplings. We find that FASER and its follow-up, FASER 2, have a full physics program, with discovery sensitivity in all of these models and potentially far-reaching implications for particle physics and cosmology.

The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, corresponding to a significance of $7.3\sigma$ when compared to $4.92\pm 0.55$ expected background events. In the Pontecorvo-Maki-Nakagawa-Sakata mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles ${\theta }_{12}$, ${\theta }_{23}$, ${\theta }_{13}$, a mass difference $\mathrm{\Delta }{m}_{32}^2$ and a $CP$ violating phase ${\delta }_{CP}$. In this neutrino oscillation scenario, assuming $|\mathrm{\Delta }{m}_{32}^2|=2.4\times {10}^{-3}{\mathrm{eV}}^2$, ${\sin }^2{\theta }_{23}=0.5$, and $\mathrm{\Delta }{m}_{32}^2>0$ ($\mathrm{\Delta }{m}_{32}^2<0$), a best-fit value of ${\sin }^{2}2{\theta }_{13}=0.140_{-0.032}^{+0.038}$ ($0.170_{-0.037}^{+0.045}$) is obtained at ${\delta }_{CP}=0$. When combining the result with the current best knowledge of oscillation parameters including the world average value of ${\theta }_{13}$ from reactor experiments, some values of ${\delta }_{CP}$ are disfavored at the 90% C.L.

Hyper-Kamiokande will be a next-generation underground water Cherenkov detector with a total (fiducial) mass of 0.99 (0.56) million metric tons, approximately 20 (25) times larger than that of Super-Kamiokande. One of the main goals of Hyper-Kamiokande is the study of $$CP$$ asymmetry in the lepton sector using accelerator neutrino and anti-neutrino beams. In this paper, the physics potential of a long-baseline neutrino experiment using the Hyper-Kamiokande detector and a neutrino beam from the J-PARC proton synchrotron is presented. The analysis uses the framework and systematic uncertainties derived from the ongoing T2K experiment. With a total exposure of 7.5 MW $$\times 10^7$$s integrated proton beam power (corresponding to $$1.56 \times 10^{22}$$ protons on target with a 30 GeV proton beam) to a $$2.5^\circ$$ off-axis neutrino beam, it is expected that the leptonic $$CP$$ phase $$\delta _{CP}$$ can be determined to better than 19 degrees for all possible values of $$\delta _{CP}$$, and $$CP$$ violation can be established with a statistical significance of more than $$3\,\sigma$$ ($$5\,\sigma$$) for $$76{\%}$$ ($$58{\%}$$) of the $${\delta _{CP}}$$ parameter space. Using both $$\nu _e$$ appearance and $$\nu _\mu$$ disappearance data, the expected 1$$\sigma$$ uncertainty of $$\sin ^2\theta _{23}$$ is 0.015(0.006) for $$\sin ^2\theta _{23}=0.5(0.45)$$.

The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km. The measurement is based on data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of \( \left( {6.5\pm 7.4\left( {\mathrm{stat}.} \right)_{-8.0}^{+8.3}\left( {\mathrm{sys}.} \right)} \right)\mathrm{ns} \) was measured corresponding to a relative difference of the muon neutrino velocity with respect to the speed of light \( {{{\left( {\upsilon -c} \right)}} \left/ {c} \right.}=\left( {2.7\pm 3.1\left( {\mathrm{stat}.} \right)_{-3.3}^{+3.4}\left( {\mathrm{sys}.} \right)} \right)\times {10^{-6 }} \). The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5 μs long extractions, was confirmed by a test performed at the end of 2011 using a short bunch beam allowing to measure the neutrino time of flight at the single interaction level.