Capturing a supernova neutrino burst: once in a lifetime

Participants at the March workshop at Virginia Tech. Credit: Tatsu Takeuchi
Participants at the March workshop at Virginia Tech. Credit: Tatsu Takeuchi
Participants at the March workshop at Virginia Tech. Credit: Tatsu Takeuchi

There is a good chance that DUNE will observe a galactic supernova during its lifetime. A second chance, however, is pretty unlikely. The collaboration’s Supernova and Low-Energy Working Group is working to make sure that the far detector is ready for this once-in-a-lifetime opportunity.

A core-collapse supernova is an extremely physics-rich environment and numerous processes imprint themselves on the neutrino signal. Which signatures are the most robust and valuable is not obvious a priori, and much careful study is required.

To identify key signatures and help determine requirements for supernova neutrino burst (SNB) physics in DUNE, the group convened a focused meeting last November at SLAC. With partial support from UC Davis, the meeting brought together numerical astrophysicists, neutrino theorists, nuclear physicists and DUNE collaboration members working on SNB neutrino detection.

The attendees discussed the status of simulations, the importance of measuring all stages of the explosion, the progenitor dependence of the signal, the impact of the nuclear equation of state, the modeling of neutrino flavor oscillations, the effects of sterile neutrinos and the possibilities for new physics.

Neutrino interactions in the detector, including the roles of de-excitation gamma and ejected nucleons, generated a lot of interest. These discussions revealed that the DAQ must be designed to keep all of the energy deposition from the events, and this information must be stored for the entire duration of the burst, which is thought to be over 10 seconds. Keeping only the energy deposited by final-state electrons would result in a systematic distortion to the high-energy part of the spectrum, which could be confused with the signatures of collective oscillations, and lead to mis-measurement of the total energy release in the collapse. Good energy resolution and millisecond timing are also required.

A community-organized workshop at Virginia Tech in March brought together SNB-focused scientists from DUNE and other experiments. The scientists compared the physics in different simulations and emphasized the importance of carrying out the modeling in 3D, with state-of-the-art Boltzmann neutrino transport and general-relativistic treatment of gravity.

The participants noted that the present-day modeling of the cross sections is inadequate and that detailed experimental measurements of the cross sections at supernova energies would greatly help to reliably model the signal. Understanding the background rate would especially help to measure the late-time cooling curve. This multi-experiment workshop also explored synergies between Water-Cherenkov and Liquid Argon detectors.

A further workshop will be held in August at the Institute for Nuclear Theory in Seattle, Washington,  at which the DUNE collaboration will be able to present the latest simulation results, drawing on the inputs from the earlier workshops, and solicit further physics ideas from the community.