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

已知有三种类型的中微子对应于三种不同类型的带电轻子。中微子的数量可以通过观察Z玻色子的衰变来确定，因为它的寿命取决于有多少种不同的味道。Z玻色子的寿命已被发现与三中微子模型相一致。然而，有许多实验结果与三中微子模型中的振荡不一致。三个主要结果是反应堆异常，这是指从核反应堆中观察到的反电子中微子明显缺乏，镓异常是指从基于镓的太阳中微子实验，SAGE和GALLEX中观察到的放射源中观察到的电子中微子明显缺乏，以及LSND和MiniBooNE实验从主要的μ子（反）中微子束中观察到的电子中微子明显过量。对于反应堆异常，观测到的反电子中微子数与预测数之比为0.938 _ 0.023。镓异常对应的比值为0.86 ~ 0.05。这两个比值与单位的偏差约为2.7，并且在低能电子中微子和几米的短基线的情况下都观察到这两个异常。LSND实验在30米的基线上进行，使用能量范围为20-53 MeV的μ子反中微子束。观测到的事件数量对应于3.8_的超额。MiniBooNE实验的基线为540 m，束流能量为700 MeV。实验用一束μ子中微子和一束μ子反中微子进行。观察到的事件分别为3.4和2.8。这些结果可以用至少一个额外的中微子态产生的振荡来解释。这第四种中微子状态可以被解释为无星系中微子（与活动中微子相反）。与活动中微子不同，无菌中微子只会通过引力而不是弱相互作用来相互作用。因此，无菌中微子不会对Z玻色子的衰变速率有所贡献，并且在通过探测器时不会产生任何形式的信号。短基线中微子（SBN）计划旨在通过确定无菌中微子是否存在来解决实验结果中的异常现象。SBN计划包括三个独立的液态氩时间投影室（LArTPC）；短基线近探测器（SBND）， MicroBooNE和ICARUS。这三个探测器分别位于距离中微子束源110 m、470 m和600 m的助推中微子束（BNB）轴线上。BNB最初由接近100%的μ子中微子组成，该项目的主要目标之一是寻找它们的出现和消失。作为近探测器，sbd将测量BNB的非振荡风味含量，确定其确切特征。此外，SBND离光束源很近，可以测量许多中微子-氩相互作用，因此有了如此大的数据样本，这些相互作用的研究可能会达到新的精度水平。MicroBooNE探测器故意靠近其前身MiniBooNe探测器，并试图复制在那里观察到的过多事件。ICARUS探测器将专注于测量光束的味道含量，并将其与SBND的结果进行比较，以确定数据中的任何差异是否可能是由于无菌中微子造成的。LArTPC允许记录粒子轨迹和相互作用的图像。在SBN的情况下，当中微子在探测器中相互作用产生粒子时，就会发生这种情况。如果产生的粒子是带电的，它们将反过来产生电离轨迹，但如果它们是中性的，它们将在不被注意的情况下穿过探测器

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