Neutrinos
Neutrinos are the smallest particles ever discovered, and a key player in the Standard Model of particle physics. Most of my physics research revolves around learning the fundamental properties of neutrinos - something we know surprisingly little about so far.
I work on two distinct but related neutrino projects. With SBND and MicroBooNE, I'm part of a collaboration studying high energy neutrinos for hints of anamolous oscillations - indications of a possible fourth type of neutrino.
Both MicroBooNE and SBND are liquid argon time projection chambers, which is a large scale, high resolution imaging detector.I also work on the NEXT experiment, a high pressure gaseous xenon time projection chamber. NEXT is a low background, precision experiment searching for neutrinoless double beta decay.
Neutrino experiments typically all share the same general features. First, neutrinos only interact via the weak force, meaning that their interaction rates are very low compared to other particle interactions via the strong and electromagetic forces. Second (and also because neutrinos only interact via the weak force), the only way to observe neutrino interactions is to detect the remnants of their interactions.
Because of the rare interaction rates, neutrino experiments all use clever techniques to increase the number of detected neutrinos compared to background events. Some experiments, particularly beam-based neutrino experiments, use an incredibly high influx of neutrinos to compensate for the very low interaction rate. Experiments like those in the SBN Program take advantage of this.
Another technique for improving neutrino experiments is to use high precision neutrino detectors, either with excellent energy resolution, high resolution imaging, or both. A time projection chamber is a technology for neutrino experiments that can use all the tricks in the book for making a great neutrino experiment: it's scalable to very large sizes, can have state of the art energy resolution, and has imaging precision that is only rivaled by bubble chambers.
MicroBooNE, SBND, and NEXT are all variations of a time projection chamber, which is an exciting technology in high energy physics.
Time Projection Chambers
Time projection chambers are important detectors in high energy physics, both historically and recently with a modern re-emergence. There are many good references on the history and workings of a time projection chamber.
The key advantage of modern time projection chambers is excellent spatial resolution and charge digitization. Many of the liquid argon time projection chambers use wires to read out rifted charge, which compresses a 3D interaction into a 2D image. However, the amplitude of each pixel in the 2D image tells a lot of information about the particles in the image. Below is one projection of the Microboone TPC showing a muon neutrino charged current interaction, with both a long muon track and shorter, hadronic tracks. One of these tracks is much more ionizing than the others, indicating it’s likely a proton.
The microboone TPC uses wires to read out it’s drifted charge, giving multiple views of the same interaction. In effect, you get three views: top down, from 60 degrees to the left, and 60 degrees to the right. In the images below, you can see how one interaction (the same as above) is changed by the difference perspectives the wire plane TPC gives.
You can see that each view offers a unique view of the event. In fact, based on this information and the geometry of the detector, you can infer from the images the path of the 3D particle interaction.
There is another style of TPC that uses pixel readouts instead of wire readouts. For example, in the NEXT experiment, they have a dense 2D array of silicon photomultiplies spaced at 1cm pitch. Combined with the drift time of an interaction, this gives natively 3D interaction information.
The interaction shown here is low energy, but you can see many distinct interaction sites from gamma rays, as well as the larger primary interaction site.