Implications of the first evidence of the Bs→μμ decay

There has been quite a lot of press interest in the recent evidence of a Bs meson decay into muon and anti-muon at the LHCb experiment, which places additional constraints on supersymmetric extensions of the standard model. There are also indirect consequences for cosmology, since supersymmetric particles are candidates for dark matter. Reading the BBC article, however, a layperson or even a beginning graduate student might worry that supersymmetry is in serious trouble, and that this implies we need an alternative to dark matter! But don’t switch your PhD to MOND just yet, reassuring comments from our resident expert John Ellis follow:

As I was quoted in the BBC article: “Supporters of supersymmetry, however, such as Prof John Ellis of King’s College London, said that the observation is “quite consistent with supersymmetry. In fact,” he said, “(it) was actually expected in (some) supersymmetric models. I certainly won’t lose any sleep over the result.””

For more details, see the MasterCode website, in particular our remark that “The new measurement provides a valuable new constraint on the supersymmetric parameter space, but the observation of a Standard Model-like branching fraction for the Bs→μμ decay is quite consistent with supersymmetry. In fact, a Standard Model-like branching fraction of this decay was expected in constrained supersymmetric models like the CMSSM or NUHM1 (see, e.g., the recent MasterCode results for further details). As a result, the favoured regions in the parameter space of these models do not change significantly after the inclusion of the new constraint.

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