6533b82efe1ef96bd1293ac7

RESEARCH PRODUCT

$$N\bar N$$ annihilation at rest into five pions

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\(N\bar N\) annihilation at rest into five pions was studied in the ASTERIX spectrometer by stopping antiprotrons from LEAR in a H2 or D2 gas target. In\(\bar pp\) annihilations in H2 leading to the π+π−π+π−π0 final state, the invariant mass spectra of two, three, and four pions show no evidence for any new narrow states. In\(\bar pn \to \pi ^ + \pi ^ - \pi ^ + \pi ^ - \pi ^ - \) the difference of the four pion mass spectra recoiling against a π− and those recoiling against a π+ shows a resonance-like structure (“ζ (1480)”), confirming a previous analysis with a smaller event sample. The ζ (1480) mass is shown to depend strongly on the momentum of the spectator proton. In H2, we searched for the ζ (1480) in the reaction\(\bar pp \to \pi ^0 \zeta \) (1480), ζ (1480) →π+π−π+π− to clarify whether the ζ (1480) is identical to the 4π-mode of thef2 (1520). No evidence for this decay mode was found. A prominent resonance in\(\bar pp\) innihilation into five pions is the ω meson. We find two quasi-two-body intermediate states:\(\bar pp \to \rho \omega \) and\(\bar pp \to \pi ^ \pm b_1^ \mp \) (1235). The mass and width of theb1 (1235) are determined to be: $$M_{bI} = 1225 \pm 5\user2{MeV, }\Gamma _{b1} = 113 \pm 12MeV.$$ (1)