Search for Mixing and CP Violation in Charm Decays at LHCb

风味振荡或混合和CP破坏是高能物理中两个最显著的现象。混合是一个中性介子（由一个夸克和一个反夸克组成）可以“翻转”成它的反物质当量的过程。CP违逆是物质和反物质之间行为的基本不对称，是解释我们所处宇宙的必要条件，因为我们所有的观测都表明，宇宙绝大多数是由物质构成的。在由s和b夸克组成的介子中观察到混合和CP破坏，但从未在任何含有c夸克的系统中观察到。目前的理论预测，这些效应确实应该存在于携带c的介子中，但在极低的水平上。用c介子观察这两种现象都将是非常令人兴奋的，因为我们还不知道的物理学对信号效应的任何贡献很可能比现有理论预测的要大。一个比预期更大的信号很可能表明这种新物理学的存在，以及它的本质。寻找这些效应将使用LHCb实验。LHCb被设计用来研究携带b介子的性质，但在这里，我们提出了新的建议，利用最近LHCb操作策略的变化来扩大实验的物理程序，包括对c介子的研究。LHCb将在一年的运行中收集的c介子数量远远超过任何以前或当代设施所能达到的数量。这使得实验对CP违逆和与这些粒子的混合具有优异的灵敏度，并为期望发现提供了良好的依据。然而，与这些现象相关的信号将非常小，因此需要付出艰苦的努力来区分与感兴趣的物理相关的信号，以及由背景过程产生的虚假效果，或者对探测器响应的误解。分解这些贡献将是一个巨大的挑战，并且将需要与从事b物理研究核心项目的LHCb物理学家所使用的技术和方法截然不同的技术和方法。Responsive RA将首先使用蒙特卡罗事件来模拟分析环境，从而确定c物理研究中将遇到的主要困难。这项工作将用于指导实验如何准确地组织数据获取操作（即“触发策略”），以最大限度地发挥c物理潜力。这项工作将在分析2007- 2008年实验的第一批数据时达到高潮，这本身将使世界上最敏感的c介子探测成为可能。

Flavour oscillation, or mixing, and CP violation are two of the most remarkable phenomena in high energy physics. Mixing is the process by which a neutral meson (constituted of a quark and an anti-quark) can 'flip' into its anti-matter equivalent. CP violation is a fundamental asymmetry in behaviour between matter and anti-matter, and is necessary to explain the universe in which we find ourselves, since all our observations indicate that the cosmos is overwhelmingly constituted of matter. Both mixing and CP violation have been observed in mesons made of s and b quarks, but never in any system containing a c quark. Present theories predict that these effects should indeed exist in c carrying mesons, but at an extremely low level. The observation of either phenomena with c mesons would be extremely exciting, because any contributions to the signal effects driven by physics we do not yet know about is very likely to be bigger than that predicted by the established theories. A larger than expected signal would very likely indicate the existence, and indeed nature, of this new physics. The search for these effects will use the LHCb experiment. LHCb has been designed to study the properties of b carrying mesons, but here we make the novel proposal to exploit recent changes in the operational strategy of LHCb to broaden the physics programme of the experiment to include the study of c mesons. The number of c mesons that LHCb will collect in a single year of operation is far in excess of that achievable in any previous or contemporary facility. This gives the experiment excellent sensitivity to CP violation and mixing with these particles, and offers good grounds for expectation of a discovery. However, the signals associated with these phenomena will be extremely small, and so painstaking effort will be needed to distinguish between the signs associated with the physics of interest, and fake effects generated by background processes, or a misunderstanding of the detector's response. Unpicking these contributions will be a great challenge, and will require very different techniques and approaches to those deployed by LHCb physicists engaged in the core programme of b physics studies. The Responsive RA will begin by using Monte Carlo events to simulate the analysis environment, and thereby identify the main difficulties which will be encountered in the c physics study. This work will be used to guide the experiment in how exactly the data taking operation (namely the 'trigger strategy') should best be organised to maximise the c physics potential. This work will culminate by analysing the first data from the experiment in 2007-8, which in itself will allow the world's most sensitive probe of the c meson sector.