[Paper Review] A Novel Cosmic Ray Tagger System for Liquid Argon TPC Neutrino Detectors

M. Auger, M. Del Tutto+14 more|arXiv (Cornell University)|Dec 14, 2016

Neutrino Physics Research3 references4 citations

TL;DR

This paper presents a novel scintillator-based Cosmic Ray Tagger (CRT) system for liquid argon time projection chamber (LArTPC) neutrino detectors in Fermilab's Short Baseline Neutrino (SBN) program. Using 16-scintillator-strip modules with wavelength-shifting fibers and silicon photomultipliers (SiPMs), the CRT achieves >95% muon detection efficiency, 1.8 cm spatial resolution, and 1.2 ns timing resolution, enabling precise tagging of cosmic rays to reduce background in neutrino interaction reconstruction.

ABSTRACT

The Fermilab Short Baseline Neutrino (SBN) program aims to observe and reconstruct thousands of neutrino-argon interactions with its three detectors (SBND, MicroBooNE and ICARUS-T600), using their hundred of tonnes Liquid Argon Time Projection Chambers to perform a rich physics analysis program, in particular focused in the search for sterile neutrinos. Given the relatively shallow depth of the detectors, the continuos flux of cosmic ray particles which crossing their volumes introduces a constant background which can be falsely identified as part of the event of interest. Here we present the Cosmic Ray Tagger (CRT) system, a novel technique to tag and identify these crossing particles using scintillation modules which measure their time and coordinates relative to events internal to the neutrino detector, mitigating therefore their effect in the event tracking reconstruction.

Motivation & Objective

• To mitigate the dominant background from cosmic ray muons crossing the active volumes of LArTPC detectors in the Fermilab SBN program.
• To improve the sensitivity of neutrino oscillation measurements by reducing false positive events from misidentified cosmic muons.
• To enable precise calibration and response characterization of the detectors using tagged cosmic muons.
• To develop a scalable, high-performance tagging system using scintillator strips, WLS fibers, and SiPMs for large-volume LArTPCs.
• To ensure consistent performance across all modules through rigorous quality assurance and calibration procedures.

Proposed method

• The CRT system uses 16 mechanically joined scintillator strips (10.8 cm wide, 0.1 mm adhesive layer) in aluminum casings, with 2 mm thick walls for mechanical stability.
• Each strip is read out by two wavelength-shifting (WLS) fibers and two SiPMs at opposite ends to enable position reconstruction via signal amplitude ratio.
• A front-end board (FEB) with a 250 MHz coarse counter and delay-chain interpolator achieves 1.2 ns RMS timing resolution for event timestamping.
• The system measures photon propagation delay in the scintillator, finding an effective delay of 6.1 ± 0.7 ns/m, which is used to correct time-of-flight measurements.
• Cosmic muons are used as calibration sources to validate position and timing resolution across different strip positions and module configurations.
• Trigger time differences between modules are measured using crossing muons, with cabling delays of 2 ns and 25 ns for adjacent and 7.3 m separated modules, respectively.

Experimental results

Research questions

• RQ1 Can a scintillator-based tagging system achieve >95% detection efficiency for cosmic muons in large-volume LArTPCs?
• RQ2 What is the achievable spatial resolution for muon position reconstruction using dual SiPM readout on scintillator strips?
• RQ3 Can the timing resolution of the FEB system be maintained at 1.2 ns RMS across different signal amplitudes and path lengths?
• RQ4 How accurately can the CRT system resolve the relative timing of cosmic muons across multiple modules separated by up to 7.3 m?
• RQ5 To what extent can the CRT system reduce false neutrino interaction reconstruction due to cosmic ray backgrounds in SBN detectors?

Key findings

• The CRT system achieves a muon detection efficiency exceeding 95% across the entire surface of each module, as confirmed by cosmic ray calibration.
• The spatial resolution of the position reconstruction is 1.8 cm, with the RMS difference between reconstructed and true hit positions minimized through signal amplitude correction.
• The timing resolution of the FEB system is 1.2 ns RMS, measured using a pulsed laser and validated at both 25 cm and 375 cm from the SiPMs.
• The effective photon propagation delay in the scintillator strips is measured to be 6.1 ± 0.7 ns/m, enabling accurate time-of-flight corrections.
• Trigger time differences between modules are consistent with expected cable delays (2 ns and 25 ns), confirming stable and predictable timing across the system.
• Quality assurance tests confirm uniform performance across all modules, with consistent detection efficiency and resolution, ensuring reliability for large-scale deployment.