The NOvA Detectors

NOva will use two detectors, one located 810 km from Fermilab on the US-Canada border in northern Minnesota and one located underground at Fermilab in the NuMI tunnels. The far detector will be 15.6 m wide 15.6 m tall and 78 m long, weighing in at 15 kilotons. Due to the much higher rates at the near site, the near detectors can be considerably smaller, 2.9 m x 4.2 m x 14.3 m, weighing in at a total of 222 tons.

The NOvA detectors are constructed from planes of PVC modules alternating between vertical and horizontal orientations. The far detector is 15.6 x 15.6 meters in size and 78 meters long. In addition to the far detector, NOvA will construct an "Integration Prototype Near Detector" which will operate in the NuMI surface building in 2008-2009. This detector will see the NuMI beam at an angle of 110 milliradians. For the physics run, NOvA will construct a near detector to be placed underground at Fermilab at the same off-axis angle as the far detector. All detector are identical in their construction, but differ in size.

The NOvA detectors are assembled from modules of extruded PVC which is loaded with titanium dioxide to enhance reflectivity. The technology is similar to that used commercially for garage doors and fencing. Modules of 32 cells are assembled by gluing two 16-cell extrusion together. Each cell has an interior size of 3.8 cm transverse to the beam direction and 5.9 cm along the direction. The length of the modules ranges from 15.6 m for the far detector to 4.2 m and 2.9 m for the NOvA near detectors.

Each cell is filled with liquid scintillator and scintillation light is collected on a 0.7 mm diameter wave-length shifting fiber. The fiber is looped inside the cell and both ends are routed to a single pixel of an avalanche photo-diode (APD) detector. At the far end of a module, NOvA will collect an average of 28 photo-electrons per muon crossing about the APD threshold of 15 photoelectrons.

The performance of the NOvA design is illustrated in the event displays. Muon-neutrino quasi-elastic events typically show two clear tracks. Electron neutrino events are typified by the presence of a "fuzzy" track with roughly 3 cells hit transversely per plane.

Sample νμ charged-current (left) and νe charged-current (right) events as simulated in the NOvA detectors. In each display, the Monte-Carlo information is shown in the top two panels and the simulated response of the detector is shown in the bottom two panels. The x-vs-z view of the event is shown in the left two panels and the y-vs-z view of the event is shown in the right two panels. In both cases the recoil proton track is seen as a short track and the lepton is seen as a long track. The electron shower is distinguished from the muon track by its "fuzzy" transverse profile.