Measurement of the neutrino oscillation parameters using Bayesian Markov Chain Monte Carlo at T2K

中微子是宇宙中最丰富的物质粒子，但人们对它们知之甚少，因为它们之间的相互作用很弱。很长一段时间以来，人们一直认为中微子是没有质量的，但大约20年来，越来越多的证据表明，不同种类的中微子可以从一种味道转变为另一种味道。这一过程被称为中微子振荡，它们在不同味道之间来回穿梭，这一发现于2015年获得了诺贝尔物理学奖，该奖项分别授予了Takaaki Kajita和Arthur B. McDonald，他们分别使用了超级神冈和SNO实验。虽然这些实验使用的是不太为人所知的自然中微子源，但T2K实验却更进一步。一束μ子中微子在日本东海岸的J-PARC加速器中心的受控环境中产生，并被定向到超级神冈探测器。激光束被测量两次，一次是在距离中微子产生目标280米远的探测器上，在中微子发生变化之前，另一次是在距离目标300公里远的超级神冈探测器上。比较两个探测器的测量值可以精确地确定振荡参数。此外，T2K用中微子和反中微子进行了这些测量，这导致了一些初步的迹象，表明振荡不相同，因此违反了cp对称性。这意味着物质和反物质的行为不一样，最终可能有助于解释宇宙的物质反物质不对称，宇宙完全是物质主导的。该论文将作为国际T2K合作的一部分进行，该合作拥有来自全球约500名成员。本文的目的是通过采用额外的数据来减少统计不确定性来改进控制中微子振荡的参数的测量，同样重要的是，减少测量的系统不确定性。学生将使用T2K振荡分析团队之一，开发新的方法，更好地处理或减少系统误差，并将其应用于现有和新的数据集。需要仔细验证这些方法，并将结果与其他分析团队的结果进行比较。它很可能是一个马尔可夫链蒙特卡罗方法将被用来寻找最优在一个高维参数空间。使用近探测器数据还没有这样做，这将允许对相关和不相关的不确定性进行更一致的处理，并同时拟合近和远探测器数据，从而提高对cp违反效应的灵敏度。

Neutrinos are the most abundant matter particle in the Universe, but very little is known about them as they only interact weakly. For a long time it had been assumed that neutrinos would be massless, but since roughly 20 years, there has been mounting evidence that the different kind of neutrinos can transform themselves from one flavour to another. The discovery of this is process called neutrino oscillations as they go forth and back between the different flavours was awarded with the Nobel Prize in Physics in 2015, which was awarded to Takaaki Kajita and Arthur B. McDonald using the SuperKamiokande and SNO experiments respectively.While these experiments were using natural not very well understood neutrino sources, T2K experiment has gone a step further. I beam of muon neutrinos is produced in a controlled environment at the J-PARC accelerator centre on the east coast of Japan and is directed to the SuperKamiokande detector. The beam is measured twice, once in a near detector 280m away from the neutrino production target before the neutrinos could change and once with the SuperKamiokande detector 300 km downstream. Comparing the measurements of both detectors allows a precision determination of the oscillation parameters. Furthermore, T2K has made these measurements with both neutrinos and anti-neutrinos and this lead to some first indications that the oscillations are not the same and thus violate the CP-Symmetry. This means that matter and anti-matter do not behave the same and may eventually help to explain the matter anti-matter asymmetry of the universe, which is entirely matter dominated.The thesis will be performed as part of the international T2K collaboration, which has around 500 members from around the globe. The aim of the thesis is to improve the measurement of the parameters governing neutrino oscillations by taking additional data to reduce the statistical uncertainty and, equally important, to reduce the systematic uncertainties of the measurement.The student will use one of the T2K Oscillation analysis teams and develop new methods that better treat the systematic errors or reduces them and apply these to existing and new data sets. The methods will need to be carefully verified and the results compared to those of alternative analysis teams. It is likely that a Markov Chain Monte Carlo approach will be used to find optima in a highly dimensional parameter space. This has not yet been done using the near detector data and would allow for a more consistent treatment of correlated and uncorrelated uncertainties and a simultaneous fit to the near and far detector data leading to an improved sensitivity to CP-violating effects.