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.