Abstrakt
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 analysis (PWA) was performed in bins of 3 pi mass and four-momentum transfer using the isobar model and the so far largest PWA model consisting of 88 waves.
A narrow peak is observed in the f(0)(980)pi channel with spin, parity and C-parity quantum numbers J(PC) = 1(++). We present a resonance- model study of a subset of the spin-density matrix selecting 3 pi states with J(PC) = 2(++) and 4(++) decaying into rho(770)pi and with J(PC) = 1(++) decaying into f(0)(980)pi.
We identify a new a 1 meson with mass (1414(-13)(+15)) MeV/c(2) and width (153(-23)(+8)) MeV/c(2). Within the final states investigated in our analysis, we observe the new a(1)(1420) decaying only into f(0)(980)pi, suggesting its exotic nature.