Photon detector system timing performance in the DUNE 35-ton prototype liquid argon time projection chamber

TL;DR

This paper evaluates the timing performance of the photon detector system in the DUNE 35-ton liquid argon TPC prototype, demonstrating sub-32 ns resolution and characterizing light attenuation over distance.

Contribution

It provides the first detailed measurement of photon detector timing resolution and light attenuation in the DUNE prototype liquid argon TPC.

Findings

Photon detector measures muon arrival times with <32 ns resolution.

Calibration pulses yield 15 ns timing resolution at 6 photo-electrons.

Scintillation light attenuation length is 155 ± 28 cm.

Abstract

The 35-ton prototype for the Deep Underground Neutrino Experiment far detector was a single-phase liquid argon time projection chamber with an integrated photon detector system, all situated inside a membrane cryostat. The detector took cosmic-ray data for six weeks during the period of February 1, 2016 to March 12, 2016. The performance of the photon detection system was checked with these data. An installed photon detector was demonstrated to measure the arrival times of cosmic-ray muons with a resolution better than 32 ns, limited by the timing of the trigger system. A measurement of the timing resolution using closely-spaced calibration pulses yielded a resolution of 15 ns for pulses at a level of 6 photo-electrons. Scintillation light from cosmic-ray muons was observed to be attenuated with increasing distance with a characteristic length of $155 \pm 28$ cm.