Systematic study of the decay rates of antiprotonic helium states

A systematic study of the decay rates of antiprotonic helium (${\overline{p}}^4{\mathrm{He}}^{+}$ and ${\overline{p}}^3{\mathrm{He}}^{+}$) at CERN Antiproton Decelerator has been made by a laser spectroscopic method. The decay rates of some of its short-lived states, namely those for which the Auger rates ${\gamma }_A$ are much larger than their radiative decay rates $({\gamma }_{\mathrm{rad}}\sim 1\mu s^{-1})$, were determined from the time distributions of the antiproton annihilation signals induced by laser beams, and the widths of the atomic resonance lines. The magnitude of the decay rates, especially their relation with the transition multipolarity, is discussed and compared with theoretical calculations.

Figure 1

Wide resonances scanned for the Auger rate deduction. Their full width at half maximum was obtained by fitting with Lorentz functions. Statistical errors are shown.

Figure 2

Experiment-theory comparison of the decay rate in logarithmic scale. All the data including past measurements [14, 15] are shown. The bold vertical dotted lines show the typical Auger rates estimated by Eq. (2). The experimental points without crossed markers show that the rates are between two experimental limits, and not directly determined (see the case of Sec. 2C). Some of the experimental error bars are too small to see.

Figure 3

Precise comparison of the complex energies of three ${\overline{p}}^4{\mathrm{He}}^{+}$ states. The difference of the experimental values from the two theories in Refs. 7, 9 are plotted in megahertz. The imaginary part plotted here is the half Auger width with negative sign, $-\frac{1}{2}({\gamma }_A∕2\pi )$. The values used for the comparison of the real part are the transition frequencies from metastable states, where the theoretical uncertainty should be very small.

Figure 4

Energy diagram of the ground-electron states (34, 31) of ${\overline{p}}^3{\mathrm{He}}^{+}$ and (35, 32) of ${\overline{p}}^4{\mathrm{He}}^{+}$, and their neighbor electron-excited states. The energy values of the ground-electron states were obtained by Ref. 5, and those of electron-excited states were obtained by Eq. (4).