Abstract.
We investigate the ground-state energy of the \(\pi^-p\) atom (pionic hydrogen) in the framework of QCD + QED. In particular, we evaluate the strong energy-level shift. We perform the calculation at next-to-leading order in the low-energy expansion in the framework of the relevant effective field theory. The result provides a relation between the strong energy shift and the pion-nucleon S-wave scattering lengths - evaluated in pure QCD - at next-to-leading order in isospin-breaking and in the low-energy expansion. We compare our result with available model calculations.
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Received: 11 June 2002 / Published online: 9 October 2002
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Gasser, J., Ivanov, M., Lipartia, E. et al. Ground-state energy of pionic hydrogen to one loop. Eur. Phys. J. C 26, 13–34 (2002). https://doi.org/10.1007/s10052-002-1013-z
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DOI: https://doi.org/10.1007/s10052-002-1013-z