Observation of a new narrow axial-vector meson $a_1(1420)$

C. Adolph, R. Akhunzyanov, M. G. Alexeev +201

The COMPASS collaboration at CERN has measured diffractive dissociation of 190 GeV/$c$ pions into the ${\pi }^{-}{\pi }^{-}{\pi }^{+}$ final state using a stationary hydrogen target. A partial-wave ana…