Bochum 2009 – scientific programme

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HK: Fachverband Hadronen und Kerne

HK 57: Hadron Structure and Spectroscopy II

HK 57.2: Talk

Wednesday, March 18, 2009, 16:45–17:00, H-ZO 30

Determination of the hadronic width of the ground state in pionic hydrogen — •Albert Hirtl — Stefan Meyer Institute for Subatomic Physics, Vienna, Austria

In a new high-precision experiment at the Paul Scherrer Institut (PSI), the hadronic shift (є_1s) and width (Γ_1s) of the ground state of pionic hydrogen, which are directly connected to the pion-nucleon isospin scattering lengths, were remeasured (PSI-Experiment R-98-01). The results can be confronted with recent work of effective field theories defined in the low-energy limit of quantum chromodynamics (QCD), such as, e. g., chiral perturbation theory (ChPT). In addition, Γ_1s is connected to the pion-nucleon coupling constant f_πN. A precisely known value for f_πN allows an accurate determination of the Goldberger-Treiman discrepancy, which constitutes a measure of chiral symmetry breaking. This contribution is mainly devoted to describe a method for an accurate extraction of the hadronic width from the π⁻H data.