Double Chooz, A Search for the Neutrino Mixing Angle theta-13

TL;DR

Double Chooz targets a precise measurement or limit on $\sin^2 2\theta_{13}$ using a two-detector reactor setup at the Chooz site to cancel reactor-flux uncertainties and reduce detector-systematics. The design features two identical detectors with gadolinium-loaded scintillator, careful shielding, and extensive calibrations, enabling sensitivities down to $\sin^2 2\theta_{13} \approx 0.03$ within ~3 years of data taking. By providing a fast, low-cost path to a robust theta-13 result, this work also lays groundwork for future CP-violation studies in the leptonic sector and explores safeguards applications via real-time antineutrino flux measurements. The study combines detailed signal modeling, an explicit error budget, and comprehensive background studies to demonstrate the feasibility and physics reach of a two-detector reactor neutrino experiment at a premier European site.

Abstract

The Double Chooz Reactor Neutrino Experiment in France plans to quickly measure the neutrino mixing angle theta-13, or limit it to sin^2 2-theta_13 less than 0.025. The physics reach, experimental site, detector structures, scintillator, photodetection, electronics, calibration and simulations are described. The possibility of using Double Chooz to explore the possible use of a antineutrino detector for non-proliferation goals is also presented.

Figures (13)

• Figure 1: Overview of the experiment site.
• Figure 2: Map of the experiment site. The two cores are separated by a distance of 140 meters. The far detector site is located 1.0 and 1.1 km from the two cores.
• Figure 3: Picture of the Double Chooz-far detector site taken in September 2003. The original CHOOZ laboratory hall constructed by EdF, located close the old Chooz A underground power plant, is still in perfect condition and could be re-used without additional civil engineering construction.
• Figure 4: 3D rendering of the Double Chooz-near site. The detector is located in a $\sim$45-meter-deep shaft, about 250--300 meters from the nuclear cores. Several civil engineering options are being studied to provide an overburden of 30 meters of rock (2.8 $\text{g/cm}^3$). Since more space will be available here than at the far site, we are studying the option of using low-radioactivity sand (70 cm) instead of the steel shielding used at Double Chooz far.
• Figure 5: The Double Chooz-far detector, at the Chooz underground site. The detector is located in the tank used for the CHOOZ experiment (7 meters high and 7 meters in diameter) which is still available. A total of 10.3 $\text{m}^3$ of a dodecane+PXE-based liquid scintillator doped with gadolinium is contained in a transparent acrylic cylinder surrounded by the $\gamma$-catcher region (22.6 m$^3$) and the buffer (114.2 m$^3$). The design goal is to achieve a light yield of about 200 pe/MeV which requires an optical coverage of about 13%, provided by the surrounding PMTs. The PMTs are mounted on the cylindrical steel structure that optically isolates the outer part of the detector, used as a muon veto (90 m$^3$), from the inner part.