Observation of Z_c (3900)⁰ in e⁺e⁻ → π⁰π⁰J/ψ

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Abstract

Using a data sample collected with the BESIII detector operating at the BEPCII storage ring, we observe a new neutral state Z_c (3900)⁰ with a significance of 10.4σ. The mass and width are measured to be 3894.8 ± 2.3 ± 3.2 MeV/c² and 29.6 ± 8.2 ± 8.2 MeV, respectively, where the first error is statistical and the second systematic. The Born cross section for e⁺e⁻ → π⁰π⁰J/ψ and the fraction of it attributable to π⁰Z_c(3900)⁰ → π⁰π⁰J/ψ in the range E_{c.m.} = 4.19-4.42 GeV are also determined. We interpret this state as the neutral partner of the four-quark candidate Z_c(3900)^±.

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Keywords

Atomic mass, Zc(3900), Causality (Physics)

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©2015 American Physical Society

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