Recent years have seen enormous progress in the physics of neutrino mixing, but several critical questions remain: What is the value of 13, the last unmeasured mixing angle in the neutrino mixing matrix? What is the mass hierarchy? Do neutrino oscillations violate CP symmetry? Why are the quark and neutrino mixing matrices so different? The value of 13 is central to each of these questions. Its value sets the scale for experiments needed to resolve the mass hierarchy and to search for CP violation. In addition, the size of 13 with respect to the other mixing angles may give insights into the origin of these angles and source of neutrino mass. Reactor experiments hold the promise of unambiguously determining the 13 mixing angle.
This proposal, from the University of Chicago, Columbia University and Barnard College, requests funds to construct the outer muon veto and tagging system for the Double Chooz neutrino oscillation experiment. The goal of the experiment is the measurement of 13 with almost an order-of-magnitude better sensitivity than the current best limit. The veto system is the main detector element used to suppress backgrounds and to understand their systematic uncertainties, which will be essential to reaching the experiment's sensitivity goal.
The Double Chooz Experiment will use two detectors near the Chooz Nuclear Power Station in France. As a result of the few MeV energy of the reactor antineutrinos, cosmogenic backgrounds are a serious issue for reactor experiments. The Double Chooz Experiment uses a two-part, inner-outer veto system to reduce and measure these backgrounds. This group proposes to construct the outer veto, a large-area system of scintillating counters placed above the detector. In addition to providing significant background suppression, the outer veto is expected to be a powerful tool in studying individual backgrounds, particularly the 9Li background which is the dominant background systematic uncertainty.
As for the Broader Impacts of this project, if the Double Chooz experiment demonstrates that 13 is nonzero, searches for CP violation will be particularly compelling. CP violation in the neutrino sector may ultimately help explain the baryon-antibaryon asymmetry in the universe through leptogenesis. Observation of any CP violation in the neutrino sector would be an important clue to one of the most fundamental questions in particle physics.
