Preparing for rare events: nnbar oscillation, proton decay

Jeremy Hewes, University of Manchester

The newly-minted Dr. Jeremy Hewes, recent graduate of the University of Manchester and a DUNE collaborator since 2013, will be coming to Fermilab as a postdoc in early 2018.

At Manchester Hewes studied neutron-antineutron (nnbar) oscillation, a Baryon-number-violating Beyond Standard Model (BSM) process in which a bound neutron spontaneously oscillates into an antineutron, producing a star-shaped topology that can be detected experimentally. DUNE, he says, would enable a search for this rare process at sensitivities that surpass current experimental limits.

“In the few years we’ve been working on nnbar oscillation, I’ve developed a standalone GENIE event generator for simulating the process, and used convolutional neural networks to distinguish Monte Carlo simulations of nnbar oscillations from atmospheric neutrino interactions, which is the dominant expected background process,” said Hewes.

Columbia University Professor Georgia Karagiorgi supervised this work.

“Jeremy has succeeded in applying novel image analysis techniques that take advantage of the DUNE FD’s high-resolution imaging of ionization energy deposition,” she said. “His results are very exciting and promising; they have demonstrated  — at least with Monte Carlo simulations — the expected high selection efficiency and high background rejection of the DUNE detector, and its high sensitivity to a particularly interesting BSM physics signal.”

Hewes has also worked on evaluating DUNE’s sensitivity to its primary physics goals, helped commission MicroBooNE’s continuous supernova readout, and developed a method for the acoustic detection of high-voltage breakdowns in liquid argon.

“When I get back to Fermilab, I’m hoping to continue working with convolutional neural networks, which have applications beyond nnbar oscillation, and implement them as a general analysis tool for DUNE,” said Hewes. “Our early results show great promise as a technique for event classification, and they’ve been successfully applied in other neutrino collaborations like NOνA, MicroBooNE and MINERνA.”

Aaron Higuera, University of Houston

University of Houston postdoc Aaron Higuera leads DUNE’s efforts in nucleon decay studies. As part of the Nucleon Decay and High-Energy Non-Accelerator Physics Working Group, he coordinates closely with the Far Detector Simulation and Reconstruction Working Group.  His work on modeling events expected from proton decay and neutrino background in the DUNE Far Detector is paving the way to a successful search for these very rare signals, according to University of Sheffield Professor Vitaly Kudryavtsev.

Since joining DUNE in April 2016, Higuera has been working with University of Houston Professor Lisa Whitehead Koerner, Professor Kudryavtsev, and Fermilab scientist Tingjun Yang, among others — “an incredible group of scientists.”  His work concentrates on the proton decay mode kaon + antineutrino, often called the golden channel for liquid argon detectors. The kaon emerging from this interaction is traceable in LArTPCs, whereas in water Cherenkov detectors it is below threshold.

“The search for proton decay is a highly important topic in DUNE’s physics program,” said Higuera. “Up to now, no evidence of proton decay has been reported and current lifetime limits for modes with a kaon in the final state are about 1033 years. The DUNE Far Detector, which will be the world’s largest cryogenic particle detector, will give us access to 1034 protons so we can test this limit.”

And of course experimental evidence of proton (nucleon) decay would constitute a revolutionary discovery in science, he added.

“Aaron is one of the most talented and hardworking young scientists in the DUNE collaboration,” said Kudryavtsev. “He regularly demonstrates his deep knowledge of the simulation and analysis techniques required for this analysis.”

Kudryavtsev sees a long and successful career ahead for Higuera. Lisa Whitehead Koerner knows where it’s going in the short term…

“Thanks to Aaron’s work, our understanding of the proton decay signal in the DUNE far detector has evolved considerably over the past year,” she said.  “There is much more to do, and we are very happy to have Aaron leading the way for this analysis.”