Search for sterile neutrinos and measurement of neutrino-argon interactions at the SBN programme

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There are three known flavours of neutrinos corresponding to the three differentflavours of charged leptons. The number of neutrinos may be determined by observing the decayof the Z boson, since its lifetime is dependent on how many different flavours there are. Thelifetime of the Z boson has been found to be consistent with a three neutrino model . Therehave, however, been a number of experimental results which are not consistent with oscillationsin a three neutrino model. The three main results are the reactor anomaly which refers to theapparent lack of anti-electron neutrinos observed from nuclear reactors, the Gallium anomalywhich refers to the apparent lack of electron neutrinos observed from radioactive sources placedin the Gallium based solar neutrino experiments, SAGE and GALLEX and the apparent excessof electron neutrinos observed by the LSND and MiniBooNE experiments from a predominantlymuon (anti)-neutrino beam . For the reactor anomaly, the ratio of the number of observed anti-electron neutrinos to the predict number was 0.938 _ 0.023. Similarly, the corresponding ratiofor the Gallium anomaly was 0.86 _ 0.05. Both of these ratios equate to about a 2.7_ deviationfrom unity and both anomalies were observed in the case of low energy electron neutrinos andover short baselines of a few meters. The LSND experiment was performed over a baseline of30 m with a beam of muon anti-neutrinos with an energy range of 20-53 MeV. The number ofevents observed corresponded to a 3.8_ excess. The MiniBooNE experiment was performed witha baseline of 540 m and with a beam energy of 700 MeV. The experiment was performed with abeam of muon neutrinos and muon anti-neutrinos. A 3.4_ and 2.8_ excess of events were observedrespectively. These results may be explained by oscillations from at least one additional neutrinostate with a mass splitting. This fourth neutrino state may be interpreted as asterile neutrino (as opposed to the active neutrinos. Unlike the active neutrinos, a sterileneutrino would only interact via gravity and not the weak interaction. As a result of this, a sterileneutrino would not contribute to the rate of decay of the Z boson and would not result in any sortof a signal when passing through a detector .The short baseline neutrino (SBN) programme aims to address the anomalies in the experimental results by establishing whether sterile neutrinos exist. The SBN programme consists ofthree separate liquid argon time projection chambers (LArTPC); the Short Baseline Near Detector(SBND), MicroBooNE and ICARUS. The three detectors are located along the axis of the boosterneutrino beam (BNB) at 110 m, 470 m and 600 m respectively from the neutrino beam source.The BNB initially consist of close to a 100% muon neutrinos and one of the primary goals ofthe programme is to look for e appearance and disappearance. As the near detector, SBNDwill measure the unoscillated flavour content of the BNB, determining its exact characteristics.Additionally, the close proximity of SBND to the beam source allows for the measurement of manyneutrino-argon interactions and thus with such a large data sample the study of these interactionsmay be performed to new levels of precision. The MicroBooNE detector is purposely positionedclose to its predecessor, the MiniBooNe detector, and is attempting to replicate the excess of eventsobserved there. The ICARUS detector will focus on measuring the flavour content of the beamand comparing it with the results of SBND to determine if any discrepancies in the data may beas a result of a sterile neutrino.LArTPC's allow images of particle trajectories and interactions to be recorded. In the caseof the SBN, this happens when a neutrino interacts in the detector, producing particles. If theproduced particles are charged, they will in turn create ionisation track, but if they are neutral,they will travel through the detector unnotice