Measurement of the branching ratio $\Gamma ({\Lambda }_b^0\to \psi (2S){\Lambda }^0)/\Gamma ({\Lambda }_b^0\to J/\psi {\Lambda }^0)$ with the ATLAS detector

Abstract

An observation of the ${\Lambda }_b^0\to \psi (2S){\Lambda }^0$ decay and a comparison of its branching fraction with that of the ${\Lambda }_b^0\to J/\psi {\Lambda }^0$ decay has been made with the ATLAS detector in proton--proton collisions at $\sqrt{s}=8$TeV at the LHC using an integrated luminosity of $20.6$fb${}^{-1}$. The $J/\psi$ and $\psi (2S)$ mesons are reconstructed in their decays to a muon pair, while the ${\Lambda }^0\to p{\pi }^{-}$ decay is exploited for the ${\Lambda }^0$ baryon reconstruction. The ${\Lambda }_b^0$ baryons are reconstructed with transverse momentum $p_{\mathrm{T}}>10$GeV and pseudorapidity $|\eta |<2.1$. The measured branching ratio of the ${\Lambda }_b^0\to \psi (2S){\Lambda }^0$ and ${\Lambda }_b^0\to J/\psi {\Lambda }^0$ decays is $\Gamma ({\Lambda }_b^0\to \psi (2S){\Lambda }^0)/\Gamma ({\Lambda }_b^0\to J/\psi {\Lambda }^0)=0.501\pm 0.033(\mathrm{stat})\pm 0.019(\mathrm{syst})$, lower than the expectation from the covariant quark model.

12 pages plus author list (28 pages total), 5 figures, 1 table, published on Physics Letters B 751 (2015) 63-80. All figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2013-08/

References in corpus (3)

• Big-Bang Nucleosynthesis
• Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
• Measurement of the parity-violating asymmetry parameter alpha_b and the helicity amplitudes for the decay Lambda_b->J/psi+Lambda with the ATLAS detector

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