# ANNIE Phase I: Neutron Background Measurements

## TL;DR

ANNIE Phase I measured neutron backgrounds in a Gd-doped water Cherenkov detector at Fermilab to ensure low background levels for future neutrino neutron multiplicity studies, utilizing novel LAPPDs.

## Contribution

First characterization of beam-correlated neutron backgrounds in a Gd-doped water Cherenkov detector using LAPPDs at Fermilab.

## Key findings

- Neutron backgrounds are sufficiently low for Phase II measurements.
- Validated the use of LAPPDs for neutron background characterization.
- Established methodology for neutron background measurement in neutrino detectors.

## Abstract

The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) is a 26-ton Gd-doped water Cherenkov detector installed in the Booster Neutrino Beam (BNB) at Fermilab. The primary physics goal of ANNIE is to study the multiplicity of final state neutrons from neutrino-nucleus interactions in water. Identifying and counting final state neutrons provides a new experimental handle to study systematic uncertainties related to the neutrino energy reconstruction in oscillation experiments. To achieve that goal ANNIE will make the first use of the novel Large Area Picosecond PhotoDetectors (LAPPDs). In Phase I, ANNIE characterised the beam-correlated neutron backgrounds in the detector and confirmed that they are sufficiently low for the Phase II physics measurements, anticipated to begin in 2019. In these proceesings the methodology and the results of Phase I will be discussed.