SBND at Sheffield

The Short Baseline Near Detector (SBND) is part of the Short Baseline Neutrino (SBN) program at Fermilab, USA, and began operations at the beginning of 2024.

On

Background

Several neutrino experiments have reported results which could be interpreted as oscillation signals with a squared-mass difference of about 1 eV², which is not consistent with the experimentally determined values for the known neutrinos.

The longest-standing of these is LSND, which measured an excess of ν̅_e events from a ν̅_μ source (μ⁺ decays at rest). Others include MiniBooNE, which observes an excess of low-energy events, and the reactor neutrino experiments, which consistently observe neutrino fluxes about 3% lower than the best available calculations (with the caveat that these calculations are challenging!). A nice summary of the global sterile neutrino oscillation data for each of the three oscillation channels (ν_μ disappearance, ν_e appearance and ν_e disappearance) can be found in this review.

If these results are indeed explained by neutrino oscillations, there must be a fourth species of neutrino, and the LEP results imply that it cannot be produced in Z decays—i.e., it is not weakly interacting ( a so-called sterile neutrino).

On the other hand, analyses of the cosmic microwave background tend to prefer three neutrino species, as shown in the figure below. There is also some tension between the appearance and disappearance results, which prefer different parameters for the fourth state, as shown in the figure.’

Therefore better data are needed to resolve the existing tension. The Fermilab Short Baseline Neutrino Program is intended to provide better data, while at the same time acting as a technology development testbed for the DUNE experiment.

It consists of three liquid argon time projection chambers (LAr TPCs) at different distances from the Fermilab Booster neutrino beam: ICARUS (imported from Gran Sasso) at 600 m, MicroBooNE at 470 m, and SBND at 110 m. Sheffield's involvement is with SBND.

SBND has a number of physics goals:

It is the reference (unoscillated beam) detector for the short-baseline neutrino oscillation measurement intended to confirm or refute the existence of a ~1 eV sterile neutrino.
‘It will record around two million neutrino interactions per year and will therefore provide precise neutrino-argon cross-section measurements which in turn will improve how these interactions are modelled
The SBND detector and electronics designs are similar to (though not identical to) the DUNE designs, and SBND is therefore an important technology demonstrator for DUNE. This is also, of course, the role played by the ProtoDUNE project at CERN, but, unlike ProtoDUNE, SBND is actually on a neutrino beamline and the events it records will therefore be very similar to DUNE events.