Speaker
Dr
Mikhail Mikhasenko
(HISKP, Universität Bonn)
Description
The discrepancy between different determinations of mass and width of the ground axial-vector state $a_1(1260)$ is a long-standing issue.
Measurements include the resonance production in hadronic processes, i.e. central production, antiproton-proton annihilation, and diffraction experiments, with COMPASS providing the most accurate determination of Breit-Wigner parameters so far.
On the other end, the cleanest source of the hadron axial sector $J^{PC} = 1^{++}$ is leptoproduction in the reaction $\tau\to3\pi\,\nu_\tau$ where the most precise data were collected by CLEO and ALEPH experiments.
In order to establish an agreement, we analyze the data using analyticity and unitarity constraints and characterize the resonance by its pole position.
In this talk, we report on an analysis of the $3\pi$ spectrum from $\tau$ decays measured by the ALEPH experiment. We also accomplished the analytical continuation of the spectral function, which is a delicate procedure as it deals with the three-body final state.
I will present the results for the $a_1(1260)$ resonance pole position extracted for the first time and discuss systematic uncertainties.
Primary author
Dr
Mikhail Mikhasenko
(HISKP, Universität Bonn)
