[Paper Review] Signal Processing in the MicroBooNE LArTPC

J. Joshi, X. Qian|arXiv (Cornell University)|Nov 1, 2015

Atomic and Subatomic Physics Research7 references3 citations

TL;DR

This paper presents a comprehensive signal processing chain for the MicroBooNE liquid argon time projection chamber (LArTPC), employing deconvolution and noise filtering to recover accurate charge and time information from raw waveforms. By modeling field and electronics responses and applying a double deconvolution technique to correct for dynamic induced charge, the method enables high-fidelity 3D event reconstruction using charge and time data from three wire planes.

ABSTRACT

The MicroBooNE experiment is designed to observe interactions of neutrinos with a Liquid Argon Time Projection Chamber (LArTPC) detector from the on-axis Booster Neutrino Beam (BNB) and off-axis Neutrinos at the Main Injector (NuMI) beam at Fermi National Accelerator Laboratory. The detector consists of a $2.5~m imes 2.3~m imes 10.4~m$ TPC including an array of 32 PMTs used for triggering and timing purposes. The TPC is housed in an evacuable and foam insulated cryostat vessel. It has a 2.5 m drift length in a uniform field up to 500 V/cm. There are 3 readout wire planes (U, V and Y co-ordinates) with a 3-mm wire pitch for a total of 8,256 signal channels. The fiducial mass of the detector is 60 metric tons of LAr. In a LArTPC, ionization electrons from a charged particle track drift along the electric field lines to the detection wire planes inducing bipolar signals on the U and V (induction) planes, and a unipolar signal collected on the (collection) Y plane. The raw wire signals are processed by specialized low-noise front-end readout electronics immersed in LAr which shape and amplify the signal. Further signal processing and digitization is carried out by warm electronics. We present the techniques by which the observed final digitized waveforms, which comprise the original ionization signal convoluted with detector field response and electronics response as well as noise, are processed to recover the original ionization signal in charge and time. The correct modeling of these ingredients is critical for further event reconstruction in LArTPCs.

Motivation & Objective

• To develop a robust signal processing chain that recovers original ionization charge and time information from raw waveforms in a LArTPC.
• To model and correct for the detector's field response and electronics transfer function to improve signal fidelity.
• To address dynamic induced charge effects from adjacent wires that distort signal amplitude and timing.
• To enable accurate 3D event reconstruction by combining charge and time information from three wire planes (U, V, Y).
• To support future large-scale LArTPC detectors by validating signal processing techniques in a prototype experiment.

Proposed method

• Model the field response using 2D GARFIELD simulations to characterize how drifting electrons induce signals on wire planes.
• Characterize the electronics response function and convolve it with the field response to model the full detector transfer function.
• Apply a Wiener filter to suppress noise while preserving signal area, ensuring charge conservation during deconvolution.
• Implement a double deconvolution method using 2D fast Fourier transforms in time and wire space to correct for dynamic induced charge from neighboring wires.
• Use charge matrix equations to resolve hit degeneracies in 2D projections by leveraging consistent charge measurements across all three wire planes.
• Integrate processed signals into a new 3D reconstruction framework, Wire-Cell Reconstruction, to improve tracking and calorimetry.

Experimental results

Research questions

• RQ1 How can the original ionization signal be accurately recovered from raw waveforms corrupted by detector and electronics responses?
• RQ2 What is the impact of dynamic induced charge from adjacent wires on signal amplitude and timing, and how can it be corrected?
• RQ3 How can charge and time information from three wire planes be combined to resolve 2D hit degeneracies in event reconstruction?
• RQ4 What signal processing techniques ensure robust noise filtering while preserving signal area and timing accuracy?
• RQ5 To what extent can the deconvolution and filtering chain enable high-precision 3D reconstruction in LArTPC detectors?

Key findings

• The signal processing chain successfully recovers the original ionization charge and time information from raw waveforms by deconvolving the combined field and electronics response.
• Noise filtering via a normalized Wiener filter preserves signal area, ensuring charge conservation and improving signal-to-noise ratio.
• Dynamic induced charge effects significantly distort signal amplitudes, especially for tracks at shallow angles, and are corrected using a double deconvolution method in time and wire space.
• The implementation of a 2D charge matrix equation effectively reduces hit degeneracy in 2D projections, enabling more accurate 3D reconstruction.
• The method enables reliable 3D event reconstruction using both charge and time information, with reconstructed charge values consistent across all three wire planes.
• The validated signal processing pipeline supports the development of future multi-kiloton LArTPC detectors by demonstrating high-fidelity signal recovery in a real-world experiment.