The fine-structure constant and other dimensionless fundamental constants can vary as a function of spacetime if an ultralight scalar field couples to the standard model. Detecting such variations may be possible by utilising the exceptional sensitivity of atomic clocks. Using data on strontium, ytterbium and caesium clock transitions collected by the National Physical Laboratory in the UK, the fine-structure constant and electron-to-proton mass ratio variations have been measured over approximately two weeks. Using these data, the first model-independent constraints on low-dimensional scalar-SM couplings have been placed. As special cases, new constraints are also extracted on models of ultralight scalar and axion-like dark matter.
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