Abstract

The general formula of the pi (-)p atom strong energy-level shift in the Is state is derived in the next-to-leading order in the isospin breaking, and in all orders in chiral expansion. Isospin-breaking corrections to the level shift are explicitly evaluated at order p(2) in ChPT The results clearly demonstrate the necessity to critically reaccess the values of the piN scattering lengths, extracted from the energy-level shift measurement by means of the potential model-based theoretical analysis. (C) 2000 Elsevier Science B.V. All rights reserved.