Abstract
The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) aims to make a unique measurement of neutron yield from neutrino-nucleus interactions and to perform R&D for the next generation of water-based neutrino detectors. In this paper, we characterize beam-induced neutron backgrounds in the experimental hall at Fermi National Accelerator Laboratory. It is shown that the background levels are sufficiently low to allow the next stage of the experiment to proceed. These measurements are relevant to other Booster Neutrino Beam (BNB) [1] experiments located adjacent to ANNIE Hall, where dirt neutrons and sky-shine could present similar backgrounds.
Highlights
The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) [2] aims to make the first detailed measurement of the number of neutrons produced by muon neutrinos interacting with nuclei
Because the algorithms used to reconstruct the photomultiplier tubes (PMTs) pulses rely on a threshold based on pulse amplitude rather than charge, the total charge collected by the two Neutron Capture Volume (NCV) PMTs for events at threshold should be distributed about some mean value (Qthresh)
Assuming that the total charge measured by the NCV PMTs is approximately a linear function of the energy deposited in the liquid scintillator, the NCV energy threshold Ethresh may be written in the form
Summary
The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) [2] aims to make the first detailed measurement of the number of neutrons produced by muon neutrinos interacting with nuclei. At concentrations of 0.1% Gd by mass, the enhanced cross-section has the added benefit of shortening the time constant for neutron capture from ∼200 μs to ∼30 μs These combined effects make Gd-loading essential to the final-state neutron multiplicity measurement. We report a first measurement of beam-correlated background neutrons in the ANNIE tank as a function of position This analysis uses data taken in a special configuration (ANNIE Phase-I) of the detector with a pure water target. We use the measured fall-off as a function of distance from the surface of the water and the tank walls in Phase-I to verify that that the proposed buffer region surrounding the optically isolated volume for the main ANNIE neutrino interaction physics program, known as Phase-II (lower panel of figure 1), provides adequate shielding from background neutrons. The techniques described in this paper will be applicable to any future water-based near detectors, especially those with Gd-loading or water-based liquid scintillators
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