The spectrum of light isovector mesons with $C=+1$ from the COMPASS experiment

Abstract

Based on the largest event sample of diffractively produced ${\pi }^{-}{\pi }^{-}{\pi }^{+}$, obtained by a pion beam of $190GeV/c$ momentum, the COMPASS collaboration has performed the most advanced partial wave analysis on multi-body final states, using the isobar model. The large number of waves included in the analysis reduces truncation effects. We have used fourteen out of a total of eighty-eight waves, to extract resonance parameters for eleven light meson candidates, most of them observed previously. The coherence of the analysis and the large variety of systematic studies has allowed to determine mass and width of most $a_J$ and ${\pi }_J$ states with six different values of $J^{PC}$ below a mass of $2.1GeV/{\mathrm{c}}^2$, with high confidence. We exploited that the production rates of resonant and non-resonant contributions in these fourteen waves vary differently with the four-momentum transfer squared in the reaction. In addition, we have performed the first isobar-freed analysis in diffraction, from which we have determined the shape of the $[\pi \pi {]}_{S-wave}$ isobar for different $J^{PC}$ of the $3\pi$ system.

arXiv comment9 pages, 7 figures, Proceedings MENU2016 (Version 2)

References in corpus (9)

• Glueballs, Hybrids, Multiquarks. Experimental facts versus QCD inspired concepts
• QCD and strongly coupled gauge theories: challenges and perspectives
• Observation of a J^PC = 1-+ exotic resonance in diffractive dissociation of 190 GeV/c pi- into pi- pi- pi+
• On the nature of $a_1(1420)$
• The COMPASS Setup for Physics with Hadron Beams
• Observation of a new narrow axial-vector meson $a_1(1420)$
• Dalitz Plot Analysis of D_s+ -> pi+ pi- pi+
• $a_1(1420)$ resonance as a tetraquark state and its isospin partner
• $a_1(1260),a_1(1420)$ and the production in heavy meson decays