Reactor antineutrino detection in Double Chooz experiment:Techniques for background reduction

Abstract A crucial task for the Double Chooz reactor antineutrino experiment is the thorough study of the different backgrounds in the detector. Newly developed background reduction techniques minimize the impact of the backgrounds on our sensitivity. Moreover, only a precision and accuracy measurement of the residual background would allow to measure the mixing angle θ 13 with high precision. Neutrino coincidence signals are imitated by signals produced in several others physics processes: accidental coincidences of single events (accidental background), as well as correlated events induced by cosmic muons, including stopping muons, fast neutrons and spallation isotopes Li 9 /He 8 . The Double Chooz collaboration has developed several techniques to reduce these backgrounds without introducing significant signal inefficiency reduction, and has managed to reject 86% of accidental background, more than 50% of Li 9 and He 8 and more than 80% of fast neutrons and stopping muons. Residual backgrounds are quantified with precision: the estimations for their final rates are 0.97 − 0.16 + 0.41 Li 9 /He 8 per day, 0.60 ± 0.05 of fast neutrons and stopping muons per day and 0.070 ± 0.005 the accidental background per day. These estimations are used as input for the fit to the measured positron spectrum used to determine θ 13 . The fit outputs are compatible with the estimated values for all backgrounds.