title: Peak Locations and Relative Phase of Different Decay Modes of the a_{1} Axial Vector Resonance in Diffractive Production.
abstract: We show that a single I=1 spin-parity J^{PC}=1^{++} a_{1} resonance can manifest itself as two separated mass peaks, one decaying into an S-wave ρπ system and the second decaying into a P-wave f_{0}(980)π system, with a rapid increase of the phase difference between their amplitudes arising mainly from the structure of the diffractive production process. This study clarifies questions related to the mass, width, and decay rates of the a_{1} resonance raised by the recent high statistics data of the COMPASS Collaboration on a_{1} production in πN→πππN at high energies.
authors.affiliation: Physics Department, Ecole Polytechnique, 91128 Palaiseau, France.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Basdevant
authors.affiliation: High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Edmond L
authors.initials: EL
authors.lastname: Berger