T2K experiment

The beam is directed towards the Super-Kamiokande far detector located 295 kilometres (183 mi) away in the city of Hida, Gifu prefecture.

Comparison of the content of different neutrino flavours in these two locations allows measurement of the oscillations probability on the way between near and far detectors.

T2K provided the first and the strongest yet constraint on δCP, rejecting at the 3σ (99.7%) significance level almost half of the possible values, ruling out the both CP conserving points at the significance level of 95% and giving a strong hint that CP violation may be large in the neutrino sector.

The strong CP violation in the neutrino sector could lead to matter excess production through the process called leptogenesis and thus such measurement would be important step to understand how the Universe were formed.

NOvA is conducted in the United States and measures accelerator neutrino oscillation at the distance of 810 km on the way between beam production place in Fermilab and far detector in Ash River, Minnesota.

Protons collide with a graphite target, producing mesons, mainly pions and kaons, which are then focused by a set of three magnetic horns and directed into a tunnel called the decay volume.

All remaining hadrons and charged leptons are stopped by a 75-ton block of graphite (so-called beam dump) and in the ground, while neutrinos travel underground towards the far detector.

The higher neutrino energies are suppressed by the off-axis configuration, decreasing the number of interactions with meson production, which are background in the oscillation analysis in the T2K experiment.

[11] The Pi-Zero (π0) Detector (P0D) contains 40 plastic scintillator module planes, which in the central part are interleaved with 2.8 cm thick bags fillable of water and thick brass sheets, and in two peripheral regions scintillator modules are sandwiched with lead sheets.

The ionisation electrons drift from the cathode to the sides of the TPC, where they are detected by the MicroMegas providing a 3D image of a path of the traversing charged particle.

The FGDs provide the active target mass for the neutrino interactions and are able to measure the short tracks of proton recoil.

[11][37] The Electromagnetic Calorimeter (ECal) surrounds the inner detectors (P0D, TPCs, FGDs) and consists of scintillator layers sandwiched with lead absorber sheets.

[11][38] The Side Muon Range Detector (SMRD) consists of scintillator modules which are inserted into the gaps in the magnet.

The SMRD records muons escaping the inner parts of the detector at large angles with respect to the beam direction.

[33][34] All the active material in the detectors is made up of plastic scintillator and is read as explained in section Signal readout.

It is a stainless steel cylindrical tank of about 40 m height and diameter, filled with 50,000 tons of water and instrumented with around 13,000 photomultiplier tubes (PMT).

Its goal is to measure muons and electrons produced in charged current quasielastic interactions (CCQE) of νμ and νe, respectively.

Due to relatively large mass, muons usually do not change their direction and thus produce a well-defined cone of Cherenkov light observed by PMTs as a clear, sharp ring.

In contrast, electrons, because of smaller mass, are more susceptible to scattering and almost always produce electromagnetic showers, observed by PMTs as a ring with fuzzy edges.

In the K2K experiment, an accelerator beam of muon neutrinos was produced at KEK facility in Tsukuba (Japan) and sent towards the Super-Kamiokande detector, located 250 km away.

[4]: 20 [45][46] The building of an additional Intermediate Water Cherenkov detector at a distance of around 2 kilometres (1.2 mi) is also considered for the HK experiment.

[47] The physics goals of T2K-II are a measurement of the oscillation parameters θ23 and Δm223 with a precision of 1.7° and 1%, respectively, as well as a confirmation at the level of 3 σ or more of the matter-antimatter asymmetry in the neutrino sector in a wide range of possible true values of δCP – the parameter responsible for the CP (matter-antimatter) asymmetry.

In addition to increasing the primary proton beam power, the current in the horns focusing secondary particles (pions, kaons, etc.)

The existing downstream part, consisting of two Fine-Grained scintillation Detectors (FGDs) and three Time Projection Chambers (TPCs), will maintain their sandwiched structure and continue to detect forward going leptons and high momentum hadrons.

The cubes are woven with a series of optical fibres designed to detect the light emitted by the particles produced during the interactions in the target.

Due to its geometry and coupled with the TOF and the HATPCs, the SuperFGD has the capability to detect fast-neutrons, which could be useful in the reconstruction of the antineutrino energy.

[50] The High Angle Time Projection Chambers (HATPCs) will surround the SuperFGD in the plane perpendicular to the incoming neutrino beam.

[54] The capability to determine track direction sense has been proven in the actual ND280 to be critical to reduce background generated outside the active inner detectors.

[57][58] The first loading of 13 tons of Gd2(SO4)3·8H2O (gadolinium(III) sulfate octahydrate) into SK water was done in July–August 2020 and lead to a 0.011% concentration of Gd.

It will also improve the detector performance for supernova explosions in our galaxy and study better matter-antimatter differences in accelerator neutrino oscillations.