First observation of long-lived $\pi^+ \pi^-$ atoms

DIRAC Collaboration

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arXiv · 1508.04712

First observation of long-lived $\pi^+ \pi^-$ atoms

DIRAC Collaboration

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Abstract

After observing and investigating the double-exotic $\pi^+\pi^-$ atom with the ground state lifetime $\tau$ of about $3 \times 10^{-15}$~s, the upgraded DIRAC experiment at the CERN PS accelerator observes for the first time long-lived states of the same atom with lifetimes of about $10^{-11}$~s and more. The number of characteristic pion pairs resulting from the breakup (ionisation) of long-lived $\pi^+\pi^-$ atoms amounts to $436\pm61$, corresponding to a signal-to-error ratio of better than 7 standard deviations. This observation opens a new possibility to measure energy differences between $p$ and $s$ atomic states and so to determine $\pi \pi$ scattering lengths.

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DIRAC Collaboration. 2015-08-19. First observation of long-lived $\pi^+ \pi^-$ atoms. https://arxiv.org/abs/1508.04712

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