First neutrinos detected at Fermilab detector

Scientists working on the Short-Baseline Near Detector (SBND) at Fermi National Accelerator Laboratory have identified the detector’s first neutrino interactions.

Edinburgh contribution to neutrino detection

Students and post-doctoral staff at the School of Physics and Astronomy are one of the largest UK groups contributing to the experiment.

The Edinburgh team members have made significant contributions to the construction of the SBND cathode with innovative wavelength-shifting foils to enhance light collections, as well as to the understanding of the cosmic-ray tracking, photon detection and trigger systems of the detector before and after its start. Edinburgh scientists were also responsible for key items of the software infrastructure of the experiment getting it ready for the detector running.

Neutrino Detectors

The SBND collaboration has been planning, prototyping and constructing the detector for nearly a decade. The detector was built by an international collaboration of 250 physicists and engineers from Brazil, Spain, Switzerland, the United Kingdom and the United States. SBND will play a critical role in solving a decades old mystery in particle physics.

SBND is the final element that completes Fermilab’s Short-Baseline Neutrino (SBN) Program which includes the ICARUS and MicroBooNE detectors. All of the detectors are types of liquid-argon time projection chambers, and each contributes to the development of this particle detection technology for the long-baseline Deep Underground Neutrino Experiment (DUNE).

Neutrinos and the Standard Model

The Standard Model is the best theory for how the universe works at its most fundamental level. But despite being a well-tested theory, the Standard Model is incomplete. And over the past 30 years, multiple experiments have observed anomalies that may hint at the existence of a new type of neutrino.

Neutrinos are the second most abundant particle in the universe, but are difficult to study because they only interact through gravity and the weak nuclear force, meaning they hardly ever show up in a detector. Neutrinos come in three types, or flavours: muon, electron and tau. Perhaps the strangest thing about these particles is that they change among these flavours, oscillating from muon to electron to tau.

Scientists have a pretty good idea of how many of each type of neutrino should be present at different distances from a neutrino source. Yet observations from a few previous neutrino experiments disagreed with those predictions, which means there could be more than the three known neutrino flavours.

The Short Baseline Neutrino Program at Fermilab will perform searches for neutrino oscillation and look for evidence that could point to this fourth neutrino.

Beyond the hunt for new neutrinos

In addition to searching for a fourth neutrino, SBND has an exciting physics program on its own.

Because it is located so close to the neutrino beam, SBND will see 7,000 interactions per day, more neutrinos than any other detector of its kind. This large data sample will allow researchers to study neutrino interactions with unprecedented precision. The physics of these interactions is an important element of future experiments that will use liquid argon to detect neutrinos.

Whenever a neutrino collides with the nucleus of an atom, the interaction sends a spray of particles careening through the detector. Physicists need to account for all the particles produced during that interaction, both those visible and invisible, to infer the properties of the ghostly neutrinos. With the detector located so close to the particle beam, it’s possible that the collaboration could see other surprises.

One of the biggest questions the Standard Model doesn’t have an answer for is dark matter. Although SBND would only be sensitive to lightweight particles, those theoretical particles could provide a first glimpse at a ‘dark sector’.

Prof Andrzej Szelc, SBND physics co-coordinator based at the School of Physics and Astronomy said:

So far ‘direct’ dark matter searches for massive particles haven’t turned anything up. Theorists have devised a whole plethora of dark sector models of lightweight dark particles that could be produced in a neutrino beam and SBND will be able to test whether these models are true.

These neutrino signatures are only the beginning for SBND. The collaboration will continue operating the detector and analysing the many millions of neutrino interactions collected  for the next several years.