Exploiting the directional sensitivity of the double Chooz near detector

In scintillator detectors, the forward displacement of the neutron in the reaction ${\overline{\nu }}_e+p\to e^{+}+n$ provides neutrino directional information as demonstrated by the CHOOZ reactor experiment with 2500 events. The near detector of the forthcoming Double Chooz experiment will collect $1.6\times {10}^5$ events per year, enough to determine the average neutrino direction with a $1\sigma$ half-cone aperture of 2.3° in one year. It is more difficult to separate the two Chooz reactors that are viewed at a separation angle $\varphi =30°$. If their strengths are known and approximately equal, the azimuthal location of each reactor is obtained with $\pm 6°$ ($1\sigma$) and the probability of confusing them with a single source is less than 11%. Five-year’s data reduce this “confusion probability” to less than 0.3%, i.e., a $3\sigma$ separation is possible. All of these numbers improve rapidly with increasing angular separation of the sources. For a setup with $\varphi =90°$ and one-year’s data, the azimuthal $1\sigma$ uncertainty for each source decreases to $\pm 3.2°$. Of course, for Double Chooz the two reactor locations are known, allowing one instead to measure their individual one-year integrated power output to $\pm 11\%$ ($1\sigma$), and their five-year integrated output to $\pm 4.8\%$ ($1\sigma$).