Precision measurement of antiprotonic hydrogen and deuterium X-rays

Abstract

X-rays from antiprotonic hydrogen and deuterium have been measured at low pressures. Using the cyclotron trap, a 105 MeV/c antiproton beam from LEAR was stopped with an efficiency of 86% in 30 mbar hydrogen gas in a volume of only 100 cm 3. The X-rays were measured with Si(Li) detectors and a Xe-CH 4 drift chamber. The strong interaction shift and broadening of the Lyman e transition and the spin-averaged 2p width in antiprotonic hydrogen was measured with unprecedented accuracy. The triplet component of the ground state in antiprotonic hydrogen was determined for the first time.

Antinucleon-nucleon interaction at next-to-next-to-next-to-leading order in chiral effective field theory

“…[90], together with values for the imaginary part of the scattering lengths that are deduced from measurements of thenp annihilation cross section in combination with the ones for pp annihilation. Here we prefer to compare our predictions directly with the measured level shifts and widths [91,92,93,94], see Table 4. For that the Trueman formula [95] was applied to the theory results with the second-order term taken into account for the S -waves.…”

Light antiprotonic atoms

“…On the one hand, the precise determination of energies and line shapes requires high statistics: this usually demands for an apparatus providing antiproton stops in high-density targets, because the exotic atoms must be formed at high rate in a small volume in order to achieve a bright X-ray source for devices of low efficiency like (rather small) solid-state detectors or high-resolution crystal spectrometers. Line yields close to saturation have been achieved by this method [4] (Fig. 2) which suggests to perform the measurements at the lowest possible density.…”

“…6). A reasonable degree of suppression of the annihilation induced background is already obtained by guard-ring Si(Li) detectors [4]. In a two week measurement, about 2000pH Lα events were accumulated in each branch of the crystal spectrometer.…”

“…The broadening was determined from the intensity balance of the L series and the Kα transition [4,13]. Already the first measurements at LEAR proved that p-wave annihilation in pH is extra ordinarily strong.…”

“…The pressure dependence of L lines makes evident the strong influence of Stark-mixing (from[4]). The pressure dependence of L lines makes evident the strong influence of Stark-mixing (from[4]).…”