Direct Measurement of Backgrounds using Reactor-Off Data in Double Chooz

Understand

Double Chooz is unique among modern reactor-based neutrino experiments studying $\bar \nu_e$ disappearance in that data can be collected with all reactors off.

• In this paper, we present data from 7.53 days of reactor-off running.
• Applying the same selection criteria as used in the Double Chooz reactor-on oscillation analysis, a measured background rate of 1.0$\pm$0.4 events/day is obtained.
• The background model for accidentals, cosmogenic $\beta$-$n$-emitting isotopes, fast neutrons from cosmic muons, and stopped-$\mu$ decays used in the oscillation analysis is demonstrated to be correct within the uncertainties.