LHCb reveals exciting hints of New Physics

17 November 2011

The LHCb experiment this week announced at the HCP Symposium in Paris a result which, if confirmed, would most likely be the first measurement performed at the LHC at CERN that cannot be understood within the long-established Standard Model of particle physics. This will require a deeper theory of 'new physics' to explain. Oxford is a founding member of the LHCb collaboration and Oxford physicists Mat Charles and Guy Wilkinson were lead analysts in the study presented in Paris.

The LHCb experiment makes precise studies of the decay properties of B and D mesons, which contain beauty and charm quarks, respectively. Among the most interesting LHCb measurements are those concerning CP violating processes, in which differences are observed in the decays of matter and anti-matter mesons. In the case of D mesons (i.e. involving charm quarks) negligible CP violation is expected in the Standard Model, whereas new physics can generate sizable enhancements. These enhancements can vary from decay mode to decay mode.

In Paris LHCb showed a result which searched for a CP violating asymmetry in the decays of D mesons to both a kaon anti-kaon pair, and to a pion anti-pion pair. These are two channels which are particularly sensitive to the effects of new physics. In order to suppress possible sources of detector bias a measurement was made of the difference in CP violation seen between the two processes. The result, a difference in asymmetries of -0.82 ± 0.24%, differs from the no CP violation hypothesis by 3.5 standard deviations. Existing theoretical predictions suggest that the maximum effect possible in the Standard Model is of the order of 0.1%.

More work is required, both on the theoretical side to improve the precision of the Standard Model prediction, and experimentally, to confirm or disprove the result. Enough new data exist to repeat the measurement with similar precision, and to cross-check it using alternative methods. The answer will come soon, and Oxford physicists will be at the forefront of this work.

For further information visit the LHCb page on the new result.