Energy level displacement of the excited state of pionic hydrogen A. N. Ivanov, M. Faber, A. Hirtl, J. Marton and N. I. Troitskaya Eur. Phys. J. A, 19 3 (2004) 413-422 Published online: 05 February 2004 DOI: 10.1140/epja/i2003-10134-y