If you've ever tried to watch a movie on an airplane, you probably found yourself cranking up the volume to hear over the rumble of the engines. Noise-canceling headphones provide a more targeted solution. They measure the incoming sound waves—in this case, those from the engines—and cancel them out by generating the right type of sound wave. This makes the "signal"—the movie—stand out more clearly over the background noise. Similarly, the team behind the MicroBooNE detector identified and filtered several noise sources. The result? By subtracting the noise from the data, the detector reveals a clear signal about neutrinos, a fundamental building block of our universe.
Using data from the first year of MicroBooNE operations, researchers identified several distinct types of excess detector noise. The analysis team developed an offline noise filter that eliminates most of the excess noise while achieving excellent signal preservation. The team recovered clean event signatures after subtracting all identified noise sources. This experience was critical in the optimization and operation of the MicroBooNE liquid-argon time projection chamber (TPC) and is already proving useful in informing the design of future liquid-argon TPC detectors.
The primary component of the MicroBooNE detector is the TPC—a large, rectangular structure that includes a set of wire planes and readout electronics housed inside a vessel filled with liquid argon. When a neutrino collides with an argon nucleus in the TPC, particles fly away from the collision site. The particles leave a trail of electrons in their wake. The displaced electrons drift toward three planes of wires—8,256 of them—in the TPC. Information about when and where the electrons hit the wires lets scientists understand the properties of the neutrino that triggered the event. That information travels as current through the wires to readout electronics. The current is amplified and shaped by custom low-power, low-noise circuits immersed in the liquid argon.
The low-noise operation of the readout electronics is critical to properly extract the distribution of the charge deposited on the wire planes of the TPC. By identifying and subtracting all sources of noise, the team recovered clean event signatures. The residual electronics noise is consistent with the cold electronics design expectations and is stable with time and uniform over the functioning channels. This noise level is significantly lower than previous experiments that used warm front-end electronics. In summer 2016, the collaboration additionally performed several hardware upgrades, with new components from Brookhaven National Laboratory and technical support from Fermilab, to mitigate the two remaining largest sources of excess noise. After the successful upgrade, the residual excess noise was largely removed.
Brookhaven National Laboratory
This work was supported by the Department of Energy, Office of Science, Offices of High Energy Physics and Nuclear Physics; the National Science Foundation; the Swiss National Science Foundation; the Science and Technology Facilities Council of the United Kingdom; and The Royal Society (United Kingdom). Additional support for the laser calibration system and cosmic ray tagger was provided by the Albert Einstein Center for Fundamental Physics. Fermilab is operated by Fermi Research Alliance, LLC under contract with the Department of Energy.
R. Acciarri et al., (MicroBooNE Collaboration), "Noise characterization and filtering in the MicroBooNE liquid argon TPC." Journal of Instrumentation 12, P08003 (2017). [DOI: 10.1088/1748-0221/12/08/P08003]