Exploiting the directional sensitivity of the Double Chooz near detector

In scintillator detectors, the forward displacement of the neutron in the reaction $bar u_e+pto e^++n$ provides neutrino directional information as demonstrated by the CHOOZ reactor experiment with 2,500 events. The near detector of the forthcoming Double Chooz experiment will collect $1.6times10^5$ events per year, enough to determine the average neutrino direction with a $1 sigma$ half-cone aperture of $2.3^circ$ in one year. It is more difficult to separate the two Chooz reactors that are viewed at a separation angle $phi=30^circ$. If their strengths are known and approximately equal, the azimuthal location of each reactor is obtained with $pm6^circ$ ($1 sigma$) and the probability of confusing them with a single source is less than 11%. Five years 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 $phi=90^circ$ and one years data, the azimuthal $1 sigma$ uncertainty for each source decreases to $pm3.2^circ$. Of course, for Double Chooz the two reactor locations are known, allowing one instead to measure their individual one-year integrated power output to $pm11%$ ($1 sigma$), and their five-year integrated output to $pm4.8%$ ($1 sigma$).