Resonance Production and $\ddot{I}€\ddot{I}€$ S-wave in $\ddot{I}{€}^{-}+p\to \ddot{I}{€}^{-}\ddot{I}{€}^{-}\ddot{I}{€}^{+}+p_{recoil}$ at 190 GeV/c

Abstract

The COMPASS collaboration has collected the currently largest data set on diffractively produced $\ddot{I}{€}^{-}\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ final states using a negative pion beam of 190 GeV/c momentum impinging on a stationary proton target. This data set allows for a systematic partial-wave analysis in 100 bins of three-pion mass, $0.5<m_{3\ddot{I}€}<2.5$ GeV/c${}^2$ , and in 11 bins of the reduced four-momentum transfer squared, $0.1<t<1.0$ (GeV/c)${}^2$ . This two-dimensional analysis offers sensitivity to genuine one-step resonance production, i.e. the production of a state followed by its decay, as well as to more complex dynamical effects in nonresonant $3\ddot{I}€$ production. In this paper, we present detailed studies on selected $3\ddot{I}€$ partial waves with $J^{PC}=0^{-+}$, $1^{++}$, $2^{-+}$, $2^{++}$, and $4^{++}$. In these waves, we observe the well-known ground-state mesons as well as a new narrow axial-vector meson $a_1(1420)$ decaying into $f_0(980)\ddot{I}€$. In addition, we present the results of a novel method to extract the amplitude of the $\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ subsystem with $I^G{J}^{PC}=0^{+}{0}^{++}$ in various partial waves from the $\ddot{I}{€}^{-}\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ data. Evidence is found for correlation of the $f_0(980)$ and $f_0(1500)$ appearing as intermediate $\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ isobars in the decay of the known $\ddot{I}€(1800)$ and $\ddot{I}{€}_2(1880)$.

96 pages