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Abstract

The reactor antineutrino experiment Double Chooz aims to provide a precise measurement of the neutrino mixing angle θ₁₃. In the analysis with one detector, accuracy in the predicted neutrino spectrum from simulation is a necessity with regard to normalization and energy shape. The detection efficiency of neutron events, which are part of the coincidence signal created by neutrinos, introduce the largest uncertainty contribution of the normalization of the experiment related to the signal detection. In order to accomplish a matching of the efficiencies observed in data and simulation, a correction of the Monte Carlo normalization and an associated systematic uncertainty are inputs in the θ₁₃ analysis. Calibration source deployments in the inner two detector volumes allow for a measurement of the neutron detection efficiency using ²⁵²Cf fission neutrons. New methods enable to compute the correction integrated over the whole volume and the corresponding uncertainty of the selection cut related efficiency. With these revised approaches a factor two improvement in the detection efficiency uncertainty was achieved. The correction of the neutron capture fraction – the capture fraction quantifies the proportion of captures on a particular element – is evaluated and tested for its robustness. Furthermore, a crosscheck of this quantity is discussed using neutrons produced by cosmic muon spallation. Finally, the uncertainty on border effects, emerging from neutron migration at the fiducial volume boundaries, is estimated by means of different Monte Carlo configurations with varying parameters and neutron physics modelings.