A new simple exotic atom, $H^{-+}$: $e^{+}$ bound to $H^{-}$ in an atomic state*

A beam of $H^-$ ions is directed along the axis of a solenoidal magnet winding. Within this magnet, cylindrical electrodes with applied potentials slow the ions to an energy of $\sim$ 50 eV in a magnetic field of $\sim$ 0.13 Tesla. This apparatus also acts as a charged particle trap. $e^+$ from a radioactive source are slowed in frozen neon, guided by magnetic fields and captured in this Surko-style accumulator with $\sim 10^7$ $e^+$ trapped and cooled for experiments. $H^-$ ions are directed through these e+ producing long-lived $H^{-+}$ atoms. $H^{-+}$ is not bound in the charged particle trap and continues with the initial momentum of the $H^-$ ion into a metal plate. Upon impact the $e^+$ quickly annihilates into back-to-back gammas. Detection of these coincident gammas indicates $H^{-+}$ that traveled the 2 meter to the detector and indicates a survival time of $\sim 5\mu s$. Typically systems with antimatter bound to matter particles have short lifetimes (and hence wide transition widths) due annihilation. Rydberg states of $H^{-+}$, however, have the long radiative lifetimes of normal matter atoms because there is little overlap of the $e^+$ wavefunction with the core. The detected rates or $H^{-+}$ are consistent with those expected for radiative recombination.