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Flavour-changing neutral currents making and breaking the standard model

Abstract

The standard model of particle physics is our best description yet of fundamental particles and their interactions, but it is known to be incomplete. As yet undiscovered particles and interactions might exist. One of the most powerful ways to search for new particles is by studying processes known as flavour-changing neutral current decays, whereby a quark changes its flavour without altering its electric charge. One example of such a transition is the decay of a beauty quark into a strange quark. Here we review some intriguing anomalies in these decays, which have revealed potential cracks in the standard model—hinting at the existence of new phenomena.

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Figure 1: Examples of FCNC decays.
Figure 2: Observation of the decay  → μ+μ.
Figure 3: Measurements of the observable in B → K+ decays.
Figure 4: Illustration of an effective field theory for b → sℓ+ decays.
Figure 5: Global fit of rare beauty decays.

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Acknowledgements

K.A.P. acknowledges support from the European Science and Technology Facilities Council under grant number ST/K001256/1; F.A. acknowledges support from the Netherlands Foundation for Fundamental Research of Matter (FOM) and the Netherlands Foundation of Scientific Research Institutes (NWO-I); M.-O.B. acknowledges support from CERN; and P.O. acknowledges support from the Swiss National Science Foundation under grant number BSSGI0_155990.

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Archilli, F., Bettler, MO., Owen, P. et al. Flavour-changing neutral currents making and breaking the standard model. Nature 546, 221–226 (2017). https://doi.org/10.1038/nature21721

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