Measurement of the branching ratio Γ(Λ0 b → ψ(2S)Λ0)/Γ(Λ0 b → J/ψΛ0) with the ATLAS detector

Aad, G. and Abbott, B. and Abdallah, J. and Abdinov, O. and Aben, R. and Krasznahorkay, Attila and Nagai, Yoshikazu and Pásztor, Gabriella and Tóth, József (2015) Measurement of the branching ratio Γ(Λ0 b → ψ(2S)Λ0)/Γ(Λ0 b → J/ψΛ0) with the ATLAS detector. PHYSICS LETTERS B, 751. pp. 63-80. ISSN 0370-2693

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Abstract

An observation of the Λ0 b → ψ(2S )Λ0 decay and a comparison of its branching fraction with that of the Λ0 b → J/ψΛ0 decay has been made with the ATLAS detector in proton–proton collisions at √s = 8 TeV at the LHC using an integrated luminosity of 20.6 fb−1. The J/ψ and ψ(2S ) mesons are reconstructed in their decays to a muon pair, while the Λ0 → pπ− decay is exploited for the Λ0 baryon reconstruction. The Λ0 b baryons are reconstructed with transverse momentum pT > 10 GeV and pseudorapidity |η| < 2.1. The measured branch- ing ratio of the Λ0 b → ψ(2S )Λ0 and Λ0 b → J/ψΛ0 decays is Γ(Λ0 b → ψ(2S )Λ0)/Γ(Λ0 b → J/ψΛ0) = 0.501 ± 0.033(stat) ± 0.019(syst), lower than the expectation from the covariant quark model.

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