The neutrinos under study in T2K are produced by a proton beam interacting with a target at J-PARC. In order to do precision studies of neutrino oscillations, it is crucial to monitor the position and size of the proton beam immediately in front of the neutrino production target, an area of intense radioactivity. In conjunction with TRIUMF the method we chose is to image the Optical Transition Radiation produced when the proton beam travels through a thin foil. (See Chapter 13 of J.D. Jackson's book "Classical Electrodynamics" for more on transition radiation.) The visible light produced at the foil is then transported several meters by mirrors through iron and concrete shielding to a region of much lower radiation background, where it is captured by a camera . The recorded image gives us a 2-dimensional snapshot of the beam profile.
A prototype OTR system was developed at York University and tested in an electron beam at NRC in Ottawa. Based on the results, the full system was designed and built at the University of Toronto and York. We installed and commissioned the system in the beamline at J-PARC in 2008 and 2009. It has proven an essential tool for tuning the proton beam and its results are being used in the overall neutrino oscillation physics analysis.
The T2K Canada collaboration (Victoria, TRIUMF, UBC, Alberta, Regina, York and Toronto) has played a prominent role in the design and construction of the Near Detector that is 280 m from the target. This detector is crucial for understanding the initial composition of the neutrino beam when it is produced at J-PARC, allowing more precise measurements of the appearance of electron neutrinos and the disappearance of muon neutrinos when the beam reaches the Super-Kamiokande detector, 295 km away. The western Canada groups are responsible for the tracker, consisting of a time projection chamber (TPC) and a fine-grained calorimeter (FGD). The T2K Canada group as a whole is currently playing a strong role in the data analysis and publication of early physics results. Some members of T2K-Canada are also members of the SK collaboration, contributing to detector studies and the reconstruction of physics events.