First Light from Beam Neutrinos on an LAPPD in ANNIE

TL;DR

The paper tackles the challenge of deploying high-time-resolution, large-area photodetectors in a real neutrino experiment. It introduces the Packaged ANNIE LAPPD (PAL) and demonstrates its integration with the ANNIE data acquisition and other detector subsystems, achieving autonomous self-triggering within a $20$ μs beam gate and synchronization to a central GPS-disciplined clock at $10$ GS/s waveform sampling for beam-correlated Cherenkov light. The study reports the first beam neutrino events detected with an LAPPD, a high-purity sample of $1{,}045$ events illuminating the LAPPD, and qualitative indications that LAPPDs can constrain muon track parameters when combined with MRD and PMT data. This work validates the system-level performance of LAPPDs under realistic operating conditions and lays the groundwork for deploying LAPPDs in future large-scale, water-based neutrino detectors with enhanced timing and spatial resolution.

Abstract

The Accelerator Neutrino Neutron Interaction Experiment (ANNIE) is both a physics experiment and a technology testbed for next-generation light-based neutrino detection. In this paper, we report the first demonstration of a fully integrated Large Area Picosecond Photodetector (LAPPD) operating in a running neutrino beam experiment. Particular focus is given to the design, commissioning, and successful deployment of the Packaged ANNIE LAPPD (PAL), a waterproof, self-triggering module incorporating fast waveform digitization and precision timing synchronized to the ANNIE detector subsystems. We identify beam-correlated LAPPD data frames consistent with charged-current neutrino interactions observed in multiple detector subsystems, establishing the first detection of neutrino-induced Cherenkov light with an LAPPD. These results validate the system-level performance of LAPPDs under realistic experimental conditions-including long-term stability, timing synchronization, and event matching with conventional PMT and muon detector systems-marking a critical step toward their deployment in future large-scale neutrino and particle detectors.

Figures (13)

• Figure 1: The ANNIE Detector.
• Figure 2: Diagram illustrating the integration of the LAPPD subsystem into the overall timing, trigger, and data flow for ANNIE. Solid red arrows show the path of data flow and solid brown arrows the path of configuration information. The 25 MHz clock signal from the GPS is shown as a solid gray arrow. All copies of the heartbeat signal are shown as dashed arrows, copies of the 125 MHz clock signal from the CTC are shown in solid blue, and copies of the beam trigger (treated as a gate by the LAPPD subsystem and as a forced readout trigger by all other systems) are shown as dotted blue arrows. The black bidirectional arrow labeled "Ext" indicates two-way communication between the CTC and PMT readout electronics, needed to extend the nominal readout window for neutrino interactions likely to contain neutrons.
• Figure 3: Photographs of the back (left) and front (right) of a PAL. The module is oriented in the direction it is deployed in the water, with the waterproof connectors pointing upward. At the top of the modules is the LVHV board, which manages power and slow controls, and routes the communications line. The LAPPD assembly consists of the LAPPD mounted onto an analog pickup board with two bridge circuits: a powered trigger card (top) and passive bridge circuit (bottom). Plugged into the back of the LAPPD assembly are the two ACDC readout cards.
• Figure 4: A cross-section showing the response of an LAPPD to a single photon.
• Figure 5: Two views of the LAPPD frame, emphasizing the mechanical elements. The only elements that directly contact the LAPPD packaging are the pogo pins of the bridge- and trigger-boards, shown in the upper panel, and the high-voltage pogo pins, which are not shown. The plastic LAPPD frame does not directly touch the LAPPD.