Search for Mixing and CP Violation in Charm Decays at LHCb

味道振荡，或混合，和CP破坏是高能物理中最显著的两个现象。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’成它的反物质等价物的过程。CP破坏是物质和反物质之间行为的根本不对称，对于解释我们所处的宇宙是必要的，因为我们所有的观察都表明宇宙绝大多数是由物质组成的。在由S夸克和b夸克组成的介子中观察到了混合和CP破坏，但在任何含有c夸克的系统中都没有观察到。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，但水平极低。用c介子观测任何一种现象都将是非常令人兴奋的，因为我们还不知道的物理驱动的信号效应的任何贡献都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一新物理的存在，甚至是自然界。对这些效应的研究将使用LHCb实验。LHCb的设计初衷是研究载b介子的性质，但在这里，我们提出了一个新的建议，利用LHCb操作策略的最新变化，扩大实验的物理方案，包括对c介子的研究。LHCB在运行一年内将收集的c介子数量远远超过任何以前或当代设施所能实现的数量。这使实验对CP破坏和与这些粒子的混合具有极好的敏感性，并为期待发现提供了良好的基础。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迹象，以及由背景过程产生的虚假效应，或者对探测器响应的误解。取消这些贡献将是一个巨大的挑战，将需要与从事b物理研究核心计划的lhcb物理学家所采用的截然不同的技术和方法。响应性RA将通过使用蒙特卡罗事件模拟分析环境开始，从而确定在c物理研究中将遇到的主要困难。这项工作将被用来指导实验如何准确地组织数据获取操作(即“触发策略”)，以最大限度地提高c物理潜力。这项工作将通过分析2007-2008年实验的第一批数据来达到高潮，这本身就将允许世界上最灵敏的探测器探测c介子部分。

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.