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

Abstract

An observation of the <math><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></math> decay and a comparison of its branching fraction with that of the <math><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></math> decay has been made with the ATLAS detector in proton–proton collisions at <math><msqrt is="true"><mi is="true">s</mi></msqrt><mo is="true">=</mo><mn is="true">8</mn><mtext is="true"> TeV</mtext></math> at the LHC using an integrated luminosity of 20.6 fb−1. The <math><mi is="true">J</mi><mo stretchy="false" is="true">/</mo><mi is="true">ψ</mi></math> and <math><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></math> mesons are reconstructed in their decays to a muon pair, while the <math><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><mi is="true">p</mi><msup is="true"><mrow is="true"><mi is="true">π</mi></mrow><mrow is="true"><mo is="true">−</mo></mrow></msup></math> decay is exploited for the <math><msup is="true"><mrow is="true"><mi mathvariant="normal" is="true">Λ</mi></mrow><mrow is="true"><mn is="true">0</mn></mrow></msup></math> baryon reconstruction. The <math><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></math> baryons are reconstructed with transverse momentum <math><msub is="true"><mrow is="true"><mi is="true">p</mi></mrow><mrow is="true"><mi mathvariant="normal" is="true">T</mi></mrow></msub><mo is="true">></mo><mn is="true">10</mn><mtext is="true"> GeV</mtext></math> and pseudorapidity <math><mo stretchy="false" is="true">|</mo><mi is="true">η</mi><mo stretchy="false" is="true">|</mo><mo is="true"><</mo><mn is="true">2.1</mn></math>. The measured branching ratio of the <math><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></math> and <math><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></math> decays is <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><mo is="true">=</mo><mn is="true">0.501</mn><mo is="true">±</mo><mn is="true">0.033</mn><mo stretchy="false" is="true">(</mo><mrow is="true"><mi mathvariant="normal" is="true">stat</mi></mrow><mo stretchy="false" is="true">)</mo><mo is="true">±</mo><mn is="true">0.019</mn><mo stretchy="false" is="true">(</mo><mrow is="true"><mi mathvariant="normal" is="true">syst</mi></mrow><mo stretchy="false" is="true">)</mo></math>, lower than the expectation from the covariant quark model.