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

SBN 项目寻找惰性中微子并测量中微子-氩相互作用

• 批准号: 2113282
• 金额: --
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2113282
• 关键词: Search; sterile; neutrinos; measurement; neutrino

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

已知的中微子有三种，分别对应于三种不同的带电轻子。中微子的数量可以通过观察Z玻色子的衰变来确定，因为Z玻色子的寿命取决于有多少种不同的味道。Z玻色子的寿命符合三中微子模型。然而，已经有一些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，它指的是从核反应堆观测到的反电子中微子的明显缺乏，镓异常，指的是在基于镓的太阳中微子实验、SAGE和GaLEX的放射源中观测到的电子中微子的明显缺乏，以及LSND和MiniBooNE实验从一个主要的介子(反)中微子束观测到的电子中微子的明显过剩。对于反应堆异常，观测到的反电子中微子数与预测值之比为0.938~0.023。同样，镓异常的对应率为0.86_0.05。这两个比率都相当于偏离单位约2.7度，在几米的短基线上，在低能电子中微子的情况下都观察到了这两个异常。LSND实验是用能量范围为20-53 MeV的Muon反中微子束在30米的基线上进行的。观测到的事件数量相当于超出3.8度。MiniBooNE实验是在基线为540m，束流能量为700 MeV的情况下进行的。这项实验是用一束Muon中微子和Muon反中微子进行的。观测到的震级分别超出3.4级和2.8级。这些结果可以用至少一个附加的中微态的质量分裂的振荡来解释。这第四个中微子状态可以解释为小行星中微子(与活跃的中微子相反)。与活跃的中微子不同，稀有中微子只会通过引力相互作用，而不是弱相互作用。因此，稀有中微子不会影响Z玻色子的衰变速度，也不会在通过探测器时产生任何形式的信号。短基线中微子(SBN)计划旨在通过确定是否存在稀有中微子来解决实验结果中的反常现象。SBN计划由三个独立的液态Ar时间投影室(LArTPC)、短基线近探测器(SBND)、MicroBooNE和ICARUS组成。这三个探测器分别位于中微子束源110米、470米和600米处的助推器中微子束(BNB)的轴线上。BNB最初由接近100%的Muon中微子组成，该计划的主要目标之一是寻找e的出现和消失。作为近距离探测器，SBND将测量BNB的非振荡气味含量，确定其确切特性。此外，SBND靠近束源，可以测量许多中微子-Ar相互作用，因此，在如此大的数据样本下，对这些相互作用的研究可能会达到新的精度水平。MicroBooNE探测器被故意放置在靠近其前身MiniBooNe探测器的位置，并试图复制那里提供的过量事件。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无菌中微子的结果。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。如果产生的粒子带电，它们将反过来产生电离轨迹，但如果它们是中性的，它们将不被注意地通过探测器