Oxford LHCb and CLEO-c

Charm Physics: D oscillations and CP Violation

The Oxford group is pioneering the study of mixing and CP violation in the charm sector on LHCb. These phenomena proceed with the participation of virtual down-type quarks, which makes the D system highly complementary in new physics searches to measurements exploiting neutral B and K mesons, where the virtual particles are up-type. The production cross-section for charm at the LHC is enormous, giving LHCb great potential in these studies.

Oscillations of neutral D mesons into their anti-particle (or 'mixing') have only been observed very recently at the B-factories, but the parameters which characterise this phenomenon (x=Δm/m, y=ΔΓ/2Γ) have not yet been well measured.

Leading tree level (left) and penguin (right) Feynman diagrams of the decay D⁰ → K^- K⁺. Interference between the two processes is a key ingredient in CP violation that can be enhanced by the participation of new heavy particles in the penguin loop.

CP violation in D decay processes has not been observed and is expected to be highly suppressed in the Standard Model. Therefore, in general, observation of an appreciable CP violating effect in the charm system would be a signature of new physics contributions.

Oxford physicists have initiated the study of charm physics at LHCb, developing a 'D^* trigger' which will lead to annual yields of 10⁷ D^*+ decays in two body D decay modes. It has been shown that this sample can be exploited to make a mixing measurement of significantly higher precision than those available from the B-factories. The statistical sensitivity of the sample will be better than 10^-3 for CP asymmetries involving singly Cabibbo suppressed transistions, which is in the regime where the Standard Model predicts an effect.

Up-to-date information on the development of charm studies at LHCb can be found in the collaboration web pages.

back to top

Web related comments - contact Andrea Contu or Edmund Smith