91Ö±²¥

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 for the known neutrinos.

The longest-standing of these is , which measured an excess of ν̅_e events from a ν̅_μ source (μ⁺ decays at rest). Others include , 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 .

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, 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. 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. 91Ö±²¥'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.

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SBND at 91Ö±²¥

The 91Ö±²¥ group plays a leading role in SBND. Our software and physics analysis responsibilities include:

• developing calibration methods aimed at using cosmic-ray muons including electron lifetime studies for argon purity measurements, electric field uniformity measurements, recombination studies and analysis tool development;
• developing the used for reconstructing the observable final states following neutrino-argon interactions; 
• developing the analysis framework to perform sterile neutrino oscillation searches with data from the full SBN program;
• planned neutrino-argon cross-section measurements with SBND data in multiple topological channels with varying lepton/hadron content; 
• studies of SBND’s sensitivity to beyond the Standard Model (BSM) searches with SBND.

On the hardware side, we currently have experts in:

• the SBND data acquisition system;
• the cosmic-ray tagging (CRT) system;
• the anode and cathode plane assemblies (APAs and CPAs).

Our historical contributions include:

• design and manufacture of the anode plane assembly (APA) frames that hold the wire readouts inside the cryostat;
• design and manufacture of wire combs, which support the wires and prevent/minimise sag in case of a drop in wire tension;
• leading roles in the TPC construction and assembly;
• electronics testing;
• quality control and quality assurance.

The current SBND group at 91Ö±²¥ consists of Vitaly Kudryavtsev, Rhiannon Jones, Anthony Ezeribe, Alexandra Moor, Henry Lay, Vu Chi Lan Nguyen, Harry Scott and Anna Beever.