The CMS and the LHCb Collaborations have announced today at the 2013 European Physical Society Conference on High Energy Physics, EPSHEP, Stockholm, Sweden, that the B0s→μμ decay is observed. The LHCb Collaboration presented already at this conference the measurement of the B0s→μμ branching fraction of (2.9+1.1-1.0)x10-9 with a significance of 4.0σ (see the 19 July 2013 news). The CMS Collaboration presented the same day a similar result giving a branching fraction of (3.0+1.0-0.9)x10-9 with a significance of 4.3σ (see CMS public page article). The results of both experiments are compatible and, therefore, a decision was taken to combine them.
The CMS and the LHCb Collaborations have obtained a combined preliminary value of the B0s→μμ branching fraction of (2.9±0.7)x10-9. Although a thorough evaluation of the combined significance has not been performed, it is clear that the B0s→μμ decay is observed (with a significance above 5σ). The result is in agreement with the Standard Model prediction of (3.56±0.30)x10-9. The image shows the CMS and LHCb results and their combination together with the results of the CDF Collaboration as well as the D0 and ATLAS Collaborations 95% CL limits which are not included in the combination.
click the image for higher resolution
The search for the B0s→μμ decay was considered as one of the most stringent tests of the Standard Model. Now it is found at a rate consistent to within 25% with that calculated within the Standard Model. This provides a fine-grained filter for the new physics models. All models of physics beyond the Standard Model will have to test their compatibility with this important result.
Read more in the plenary presentation in Stockholm, in the LHCb paper and also in the CERN Quantum Diaries in English and French.