Pole position of the a1(1260) resonance in a three-body unitary framework*

Masses, widths, and branching ratios of hadronic resonances are quantified by their pole positions and residues with respect to transition amplitudes on the Riemann sheets of the complex energy plane. We utilize a manifestly 3-body unitary model to determine the pole position of the a1(1260) meson from the ALEPH experiment by allowing for πρ coupled channels in S- and D-wave. We find it to be (1232+15+9 −0−11 − i266+0+15 −22−27) MeV.