Search for Mixing and CP Violation in Charm Decays at LHCb

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics


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.


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