We are currently working in two areas: 1) exploring the physics case for an intermediate water Cherenkov detector and 2) contributing to the development of a new calibration system based on LED's as a light source.
Near Detector Studies
The use of a near detector(s) to constrain the flux and neutrino interaction cross-section uncertainties is essential in order for Hyper-K to reach the sensitivity needed to achieve the physics goals. Ideally the near detector would be a water target in order to eliminate the uncertainties from nuclear effects introduced when applying near detector measurements to a far detector made of different material. The Tokai Intermediate Tank for Unoscillated Spectrum (TITUS) is a 2 kt water Cherenkov detector located about 2 km from the target at the same off-axis angle as the far detector. The design is large enough to contains muons in the momentumm range of interest for the far detector measurements and far enough away from the target that pile-up of inteactions within a beam bunch is not a problem. The current detector design is shown below where the water tank (shown in blue) is surrounded by either a Muon Range Detector or a Magnetised Iron Neutrino Deetctor (reda). Warwick contributions have focussed on the idea of doping the water in TITUS with Gadolinium as a way to distinguish neutrinos from anti-neutrinos - this is especially important for the CP violation measurement where the wrong-sign contribution to the neutrino flux has to accurately determined. Warwick simulation studies have quantified the gains in CP-physics reach that such a detector might be expected to bring.
Light Readout Calibration System Development
An essential aspect of the far detector is the precise calibration of the water target for attenuation and scattering effects and to evaluate the timing response and charge linearity performance of the electronic chain. The calibration techniques used by Super-K may not be optimal for the Hyper-K environment and so, working together with the Liverpool and Sheffield groups, we are developing a new system based on injecting light pulses of known emission time and intensity at several visible wavelengths based on LED's as a light source. The schematic below shows the components of the calibration system - Warwick primarily responsible for the optical fibre delivery of the light pulses into the water tank.