Measurement of the branching ratio <math><mi mathvariant="normal" is="true">Γ</mi><mo stretchy="false" is="true">(</mo><msubsup is="true"><mrow is="true"><mi mathvariant="normal" is="true">Λ</mi></mrow><mrow is="true"><mi is="true">b</mi></mrow><mrow is="true"><mn is="true">0</mn></mrow></msubsup><mo stretchy="false" is="true">→</mo><mi is="true">ψ</mi><mo stretchy="false" is="true">(</mo><mn is="true">2</mn><mi is="true">S</mi><mo stretchy="false" is="true">)</mo><msup is="true"><mrow is="true"><mi mathvariant="normal" is="true">Λ</mi></mrow><mrow is="true"><mn is="true">0</mn></mrow></msup><mo stretchy="false" is="true">)</mo><mo stretchy="false" is="true">/</mo><mi mathvariant="normal" is="true">Γ</mi><mo stretchy="false" is="true">(</mo><msubsup is="true"><mrow is="true"><mi mathvariant="normal" is="true">Λ</mi></mrow><mrow is="true"><mi is="true">b</mi></mrow><mrow is="true"><mn is="true">0</mn></mrow></msubsup><mo stretchy="false" is="true">→</mo><mi is="true">J</mi><mo stretchy="false" is="true">/</mo><mi is="true">ψ</mi><msup is="true"><mrow is="true"><mi mathvariant="normal" is="true">Λ</mi></mrow><mrow is="true"><mn is="true">0</mn></mrow></msup><mo stretchy="false" is="true">)</mo></math> with the ATLAS detector

Alconada Verzini, María Josefina; Alonso, Francisco; Arduh, Francisco Anuar; Dova, María Teresa; Monticelli, Fernando Gabriel; Wahlberg, Hernán Pablo; The ATLAS Collaboration

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Measurement of the branching ratio $Γ (Λ_{b}^{0} \to ψ (2 S) Λ^{0}) / Γ (Λ_{b}^{0} \to J / ψ Λ^{0})$ with the ATLAS detector

2015

Tipo de documento: Articulo

Resumen

An observation of the $Λ_{b}^{0} \to ψ (2 S) Λ^{0}$ decay and a comparison of its branching fraction with that of the $Λ_{b}^{0} \to J / ψ Λ^{0}$ 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 $J / ψ$ and $ψ (2 S)$ mesons are reconstructed in their decays to a muon pair, while the $Λ^{0} \to p π^{-}$ decay is exploited for the $Λ^{0}$ baryon reconstruction. The $Λ_{b}^{0}$ baryons are reconstructed with transverse momentum $p_{T} > 10 GeV$ and pseudorapidity $| η | < 2.1$ . The measured branching ratio of the $Λ_{b}^{0} \to ψ (2 S) Λ^{0}$ and $Λ_{b}^{0} \to J / ψ Λ^{0}$ decays is $Γ (Λ_{b}^{0} \to ψ (2 S) Λ^{0}) / Γ (Λ_{b}^{0} \to J / ψ Λ^{0}) = 0.501 \pm 0.033 (stat) \pm 0.019 (syst)$ , lower than the expectation from the covariant quark model.