Minimising Systematic Uncertainties in the Determination of Theta_13 at T2K

中微子是最神秘的基本粒子。这些电中性轻子几乎没有质量，只通过微弱的核力相互作用，因此它们极难被探测到。然而，它们在地球、大气层、太阳和宇宙中都有大量的创造。中微子在加热地球、让太阳发光、让超新星爆炸的过程中发挥着关键作用。尽管中微子无处不在，但它们的本征性质多年来一直困扰着我们。由于过去十年的一系列令人兴奋的发现，我们现在知道，中微子的难以捉摸的行为探索了粒子物理学中最深层次的问题。研究物质的最基本成分，以及它们如何相互作用，是粒子物理学的主要挑战。目前该领域的知识总和被称为标准模型，它在描述微观宇宙方面取得了显著的成功。该模型包含两大类积木：夸克和轻子。例如，质子由三个夸克组成，而电子和中微子是轻子的类型。然而，我们知道标准模型是不完整的，因为必须有一个更基本的理论来解释这两大类构建块是如何相互关联的。对这两个部门性质的精确测量为我们提供了基本理论形式的最佳线索。但这不是点缀I和跨越T的问题；还有很多工作要做。1998年，轻子领域出现了一个重大惊喜：观察到这三种中微子从一种变成了另一种。这种振荡只有在中微子有质量并且相互混合的情况下才有可能，这要归功于量子力学的一个有趣的扭曲。最近的这一发现是中微子质量的第一个实验证据，在理论上很有吸引力，因为几十年来人们已经知道夸克可以相互混合。揭示夸克和轻子扇区之间的相似之处将有助于揭示基本理论的更深层次对称性。中微子之间或夸克之间的混合物理可以用六个独立的参数来描述。第一代中微子振荡实验测量了六个中微子中的四个。要捕捉剩下的两个参数，将需要以前所未有的精度进行测量。在日本T2K实验的领导下，下一代将改进现有四个参数的精度，并从2009年开始，T2K将做出世界上最好的尝试来测量剩余的未知数。了解中微子的神秘性质可能会照亮通向超越标准模型的基本理论的道路。我们现在正在着手一项大胆的计划，以提高中微子混合测量的准确性。这是向回答粒子物理关键问题迈出的必要的下一步。

Neutrinos are the most mysterious of the fundamental particles. These electrically neutral leptons are nearly massless and only interact via the weak nuclear force, so they are exceedingly hard to detect. However, they are created copiously in the earth, in the atmosphere, in the sun, and out in the cosmos. Neutrinos are key players in the processes that heat the earth, make the sun shine, and make supernovae explode. Despite the fact that neutrinos are everywhere, their intrinsic properties have puzzled us for years. Thanks to a series of exciting discoveries over the past decade, we now know that the elusive behavior of neutrinos probes the deepest questions in particle physics. Studying the most basic constituents of matter, and how they interact with each other, is the primary challenge of particle physics. The current sum of knowledge in the field is called the Standard Model, and it has been remarkably successful in describing the microscopic universe. The model contains two major classes of building blocks: quarks and leptons. For example, protons are made of three quarks, while electrons and neutrinos are types of leptons. However, we know that the Standard Model is incomplete because there must be a more fundamental theory that explains how the two major classes of building blocks are related to each other. Precise measurements of the properties of these two sectors provide our best clues to the form of the underlying theory. But it's not a matter of dotting the i's and crossing the t's; much work remains to be done. In 1998 there was a major surprise in the lepton sector: the three kinds of neutrinos were observed to change from one into another. This kind of oscillation is only possible if neutrinos have mass and mix with each other, thanks to an interesting twist of quantum mechanics. This recent discovery was the first experimental evidence for neutrino mass, and is theoretically attractive because it has been known for decades that the quarks can mix with each other. Uncovering the similarities between the quark and lepton sectors will help to reveal the deeper symmetries of the fundamental theory. The physics of mixing between neutrinos---or between quarks---can be described in terms of six independent parameters. The first generation of neutrino oscillation experiments measured four of the six. To capture the remaining two parameters will require measurements with unprecedented accuracy. The next generation, led by the T2K experiment in Japan, will improve upon the precision of the existing four parameters, and, starting in 2009, T2K will make the world's best attempt to measure the remaining unknowns. Understanding the mysterious properties of neutrinos may illuminate the way to the fundamental theory beyond the Standard Model. We are now embarking on a bold programme to improve the accuracy of neutrino mixing measurements. This is a necessary next step toward answering the key questions of particle physics.