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arXiv · 1605.06103

Observation of $\pi^- K^+$ and $\pi^+ K^-$ atoms

DIRAC Collaboration
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Abstract

The observation of hydrogen-like $\pi K$ atoms, consisting of $\pi^- K^+$ or $\pi^+ K^-$ mesons, is presented. The atoms have been produced by 24 GeV/$c$ protons from the CERN PS accelerator, interacting with platinum or nickel foil targets. The breakup (ionisation) of $\pi K$ atoms in the same targets yields characteristic $\pi K$ pairs, called "atomic pairs", with small relative momenta in the pair centre-of-mass system. The upgraded DIRAC experiment has observed $349\pm62$ such atomic $\pi K$ pairs, corresponding to a signal of 5.6 standard deviations.

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DIRAC Collaboration. 2016-05-19. Observation of $\pi^- K^+$ and $\pi^+ K^-$ atoms. https://doi.org/10.1103/physrevlett.117.112001

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