论文标题
通过铁与冰：在Icecube中微子观测站寻找无菌中微子
Through Iron & Ice: Searching for Sterile Neutrinos at the IceCube Neutrino Observatory
论文作者
论文摘要
尽管过去半个世纪我们对中微子的理解迅速发展，但他们的性质尚不清楚。这使中微子成为超越标准模型（BSM）物理学的最有希望的门户，并且中微子已经提供了富有成果的惊喜。 在过去的三十年中，许多中微子实验观察到异常振荡信号与$Δm^2 \ sim 1 \ sim 1 \ \ textrm {ev}^2 $一致，激励存在和寻找无菌中间的中子。另一方面，其他实验未能看到这样的信号。 在本文中，我们提出了两个分析。首先是对无菌中微子全球的更新，其中包括最近的实验数据。我们发现，与NULL相比，3+1模型可以更好地适合全局数据集，而$Δχ^2 = 51 $的改善仅增加了3个自由度，相当于$6.6σ$。虽然有实质性的改进，但我们还发现了使用参数拟合测试计算的5.1σ$的数据集之间的不可调和的张力。这激发了扩展模型的探索：3+2模型和3+1+衰减模型。 在3+2型号中，我们发现拟合度可以忽略不计，甚至$5.5σ$的紧张局势更加糟糕。在更外来的3+1+衰减模型中，我们发现张力减少到$3.6σ$。与3+1模型相比，仅引入一个附加参数，但张力仍然太大而无法缓解问题。 第二个分析是扩展的Icecube无菌中微子搜索的结果。以前的无菌中微子搜索没有发现无菌中微子的证据，发现P值为8％。在三个无菌混合角度中，$θ_{14}，θ_{24} $和$θ_{34} $，仅适合$θ_{24} $，因为$θ_{14} $可忽略不计，$θ_{34} = 0 $被认为是保守的假设。我们介绍了一个分析的结果，其中我们将$θ_{34} $包含在拟合模型中。进行了常见主义者和贝叶斯分析，根据质量方分裂$Δm_{41}^2 $以及混合矩阵参数$ | u _ _ {\ mu4} |^2 $和$ | U _ {\ tau4} |^2 $。频繁的分析发现最适合$Δm_{41}^2 = 5.0 \ \ \ \ \\ textrm {ev}^2 $，$ | u _ {\ mu4} |^2 = 0.04 $，和$ | U _ {\ tau4} |伪证明表明P值较小2.7％。贝叶斯分析在$δm_{41}^2 = 5.0 \ \ textrm {ev}^2 $，$ | u _ {\ mu4} |^2 = 0.02 $，$ | u _ {\ tau4} |^2 = 0.006 $'''''零假设。
Despite the rapid progression in our understanding of neutrinos over the last half century, much is left unknown about their properties. This leaves neutrinos as the most promising portal for Beyond Standard Model (BSM) physics, and neutrinos have already provided fruitful surprises. A number of neutrino experiments in the last three decades have observed anomalous oscillation signals consistent with a mass-squared splitting of $Δm^2 \sim 1\ \textrm{eV}^2$, motivating the existence and search for sterile neutrinos. On the other hand, other experiments have failed to see such a signal. In this thesis, we present two analyses. The first is an update to the sterile neutrino global fits with the inclusion of recent experimental data. We find that the 3+1 model provides a better fit to the global data set compared to the null, with an improvement of $Δχ^2 = 51$ with the addition of only 3 degrees of freedom, corresponding to $6.6σ$. While a substantial improvement, we also find a irreconcilable tension between the data sets of $5.1σ$, calculated using the parameter goodness-of-fit test. This motivates the exploration of expanded models: a 3+2 model, and a 3+1+Decay model. In the 3+2 model, we find negligible improvement to the fit, and an even worse tension of $5.5σ$. In the more exotic 3+1+Decay model, we find the tension reduced to $3.6σ$. While a substantial improvement compared to the 3+1 model with the introduction of only one additional parameter, the tension is still too large to assuage concerns. The second analysis is the results of an expanded IceCube sterile neutrino search. A previous sterile neutrino search found no evidence for sterile neutrinos, finding a p-value of 8%. Of the three sterile mixing angles, $θ_{14}, θ_{24}$, and $θ_{34}$, only $θ_{24}$ was fitted for, as $θ_{14}$ was negligible and $θ_{34} = 0$ was considered a conservative assumption. We present results of an analysis where we include $θ_{34}$ to the fitted model. Both a frequentist and Bayesian analysis were conducted, with fits done in terms of the mass-squared splitting $Δm_{41}^2$ and the mixing matrix parameters $|U_{\mu4}|^2$ and $|U_{\tau4}|^2$. The frequentist analysis finds a best fit at $Δm_{41}^2 = 5.0\ \textrm{eV}^2$, $|U_{\mu4}|^2 = 0.04$, and $|U_{\tau4}|^2 = 0.006$, with a p-value of 5.2% assuming Wilks' Theorem with 3 degrees of freedom. Pseudoexperiments are indicating a smaller p-value 2.7%. The Bayesian analysis finds a similar best fit point at $Δm_{41}^2 = 5.0\ \textrm{eV}^2$, $|U_{\mu4}|^2 = 0.02$, and $|U_{\tau4}|^2 = 0.006$, with a Bayes factor indicating a ``Very Strong'' preference for this sterile hypothesis over the null hypothesis.
