Reconstruction of neutrino events in the Accelerator Neutrino Neutron Interaction Experiment: Part I

TL;DR

The paper presents a baseline neutrino event reconstruction approach for the ANNIE detector using a compact gadolinium-loaded water tank, PMT arrays, and a downstream MRD to reconstruct muon tracks from BNB νμ CC0π interactions. It details the detector layout, simulation framework (GENIE with WCSim), and data-driven tuning using Michel electrons and through-going muons, followed by MRD-based tracking and Cherenkov-ring edge vertexing to determine the interaction vertex and muon energy with ~60 cm vertex resolution, ~13.2° angular resolution, and ~10% energy resolution. The study establishes a practical methodology for combining PMT pattern recognition with MRD tracking in a small-scale Cherenkov detector and sets a baseline against which future integration of LAPPDs (60–70 ps timing) and WbLS (enhanced light yield) can be measured. This work enables early cross-section measurements for CC interactions that produce muons stopping in the MRD and informs the impact of new technologies on event reconstruction in next-generation detectors.

Abstract

The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) was designed to reconstruct neutrino events from the Fermilab Booster Neutrino Beam (BNB) with the parallel goals of measuring neutron production in interactions with oxygen and serving as a testbed for new technology. The ANNIE detector consists of a 26-ton water Cherenkov target tank instrumented with conventional photomultiplier tubes (PMTs), a downstream tracking muon spectrometer, and an upstream double wall of plastic scintillator to serve to veto charged particles incoming from neutrino events that occur upstream of the experimental setup. ANNIE has also deployed multiple Large-Area Picosecond PhotoDetectors (LAPPDs) and a test vessel of water-based liquid scintillator (WbLS). This paper describes the event reconstruction performance of the detector before implementation of these novel technologies, which will serve as a baseline against which their impact can be measured. That said, even the techniques used for event reconstruction using only the conventional PMT array and muon spectrometer are significantly different than those used in other water Cherenkov detectors due to the small size of ANNIE (which makes nanosecond-scale timing not as useful as in a large detector) and the availability of reconstruction information from the tracking muon spectrometer. We demonstrate that combining the information from these two elements into a single fit using only pattern recognition yields a muon vertex uncertainty of 60 cm, a directional uncertainty of 13.2 degrees, and energy reconstruction uncertainty of about 10\% for BNB muon neutrino Charged Current Zero Pion (CC0pi) events.

Figures (16)

• Figure 1: A schematic drawing of the ANNIE detector system. The neutrino beam enters from the left and then passes through the three major detector subsystems: (i) the Front Muon Veto, (ii) the Gd-loaded target tank instrumented with PMTs and LAPPDs, and (iii) the Muon Range Detector.
• Figure 2: (Left) The 3D design of the ANNIE detector and (Right) an image of the inner structure in a clean room environment after all the PMTs have been mounted. Hamamatsu 10-inch PMTs are in blue and grey, Hamamatsu 8-inch PMTs are in red on the sides, and ETEL 11-inch PMTs are in red at the top. The ETEL PMTs were a prototype model that did not go into commercial production. Information on the performance can be found in Reference etel. The green rectangles represent notional and not actual LAPPD positions.
• Figure 3: (Left) Muon Range Detector: 11 alternating vertical and horizontal layers of scintillating paddles with a 5 cm iron absorber in between the layers to range out muons originating from the neutrino interactions in the tank. (Right) Front Muon Veto: Two layers of scintillator paddles designed to detect and reject muons produced in the dirt upstream of the detector
• Figure 4: An outline of how beam events are simulated in ANNIE. BNB flux files from SciBooNE and ANNIE's geometry files are read by GENIE. GENIE generates neutrino events, along with information such as positions, daughter particles, energies, and momenta. WCSim then takes this information and propagates the particles throughout the detector and generates the detector response. Output files with the same format as the actual data files are created and can be used for analysis with MC.
• Figure 5: (Left) Scan of $\chi^2/DOF(=40)$ value versus $r_{CE}$. (Right) comparison of Michel electron deposited p.e. for Data and WCSim after tuning with $r_{CE}=1.3$.