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SpringerOpen, The European Physical Journal C, 8(80), 2020

DOI: 10.1140/epjc/s10052-020-8078-4

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Observation of X(2370) and search for X(2120) in $J/ψ → γ K{\bar{K}} η '$

Journal article published in 2020 by M. Ablikim, M. N. Achasov, P. Adlarson, S. Ahmed, M. Albrecht, M. Alekseev, A. Amoroso, Q. An, Anita, Y. Bai, O. Bakina, R. Baldini Ferroli, I. Balossino, Y. Ban, K. Begzsuren and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

AbstractUsing a sample of $1.31\times 10^{9} ~J/ψ $1.31×109J/ψ events collected with the BESIII detector, we perform a study of $J/ψ → γ K{\bar{K}}η '$J/ψ→γKK¯η′. X(2370) is observed in the $K{\bar{K}}η '$KK¯η′ invariant-mass distribution with a statistical significance of $8.3σ $8.3σ. Its resonance parameters are measured to be $M=2341.6± 6.5 \, \text {(stat.)} ± 5.7 \, \text {(syst.)}~ \hbox {MeV}/c^{2}$M=2341.6±6.5(stat.)±5.7(syst.)MeV/c2 and $Γ = 117± 10 \, \text {(stat.)}± 8 \, \text {(syst.)}~\hbox {MeV}$Γ=117±10(stat.)±8(syst.)MeV. The product branching fractions for $J/ψ → γ X(2370),X(2370)→ K^{+}K^{-}η '$J/ψ→γX(2370),X(2370)→K+K-η′ and $J/ψ → γ X(2370),X(2370)→ K_{S}^{0}K_{S}^{0}η '$J/ψ→γX(2370),X(2370)→KS0KS0η′ are determined to be $(1.79± 0.23\, \text {(stat.)}± 0.65\,\text {(syst.)})\times 10^{-5}$(1.79±0.23(stat.)±0.65(syst.))×10-5 and $(1.18± 0.32\, \text {(stat.)}± 0.39\, \text {(syst.)})\times 10^{-5}$(1.18±0.32(stat.)±0.39(syst.))×10-5, respectively. No evident signal for X(2120) is observed in the $K{\bar{K}}η '$KK¯η′ invariant-mass distribution. The upper limits for the product branching fractions of ${\mathcal {B}}(J/ψ → γ X(2120)→ γ K^{+} K^{-} η ')$B(J/ψ→γX(2120)→γK+K-η′) and ${\mathcal {B}}(J/ψ → γ X(2120)→ γ K_{S}^{0} K_{S}^{0} η ')$B(J/ψ→γX(2120)→γKS0KS0η′) are determined to be $1.49\times 10^{-5}$1.49×10-5 and $6.38\times 10^{-6}$6.38×10-6 at the 90% confidence level, respectively.