Identifying physics beyond SMEFT in the angular distribution of Λb→Λc(→Λπ)…

In the Standard Model effective field theory (SMEFT), the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>S</a:mi><a:mi>U</a:mi><a:mo stretchy="false">(</a:mo><a:mn>2</a:mn><a:msub><a:mo stretchy="false">)</a:mo><a:mi>L</a:mi></a:msub><a:mo>×</a:mo><a:mi>U</a:mi><a:mo stretchy="false">(</a:mo><a:mn>1</a:mn><a:msub><a:mo stretchy="false">)</a:mo><a:mi>Y</a:mi></a:msub></a:math> symmetry of the Standard Model is linearly realized. However, it is possible that more general effective field theories, such as the Higgs effective field theory (HEFT) where this symmetry is realized nonlinearly, are needed to describe the data. Identifying physics beyond SMEFT could shed light on the nature of Higgs and the realization of the electroweak symmetry. We explore the possibility of such an identification by studying the effects of scalar and vector new physics operators on the angular distribution of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:msub><g:mi mathvariant="normal">Λ</g:mi><g:mi>b</g:mi></g:msub><g:mo stretchy="false">→</g:mo><g:msub><g:mi mathvariant="normal">Λ</g:mi><g:mi>c</g:mi></g:msub><g:mo stretchy="false">(</g:mo><g:mo stretchy="false">→</g:mo><g:mi mathvariant="normal">Λ</g:mi><g:mi>π</g:mi><g:mo stretchy="false">)</g:mo><g:mi>τ</g:mi><g:msub><g:mover accent="true"><g:mi>ν</g:mi><g:mo stretchy="false">¯</g:mo></g:mover><g:mi>τ</g:mi></g:msub></g:math>. This decay is sensitive to the six-dimensional effective operator <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:msubsup><r:mi>O</r:mi><r:mi>V</r:mi><r:mrow><r:mi>L</r:mi><r:mi>R</r:mi></r:mrow></r:msubsup><r:mo>≡</r:mo><r:mo stretchy="false">(</r:mo><r:mover accent="true"><r:mi>τ</r:mi><r:mo stretchy="false">¯</r:mo></r:mover><r:msup><r:mi>γ</r:mi><r:mi>μ</r:mi></r:msup><r:msub><r:mi>P</r:mi><r:mi>L</r:mi></r:msub><r:msub><r:mi>ν</r:mi><r:mi>τ</r:mi></r:msub><r:mo stretchy="false">)</r:mo><r:mo stretchy="false">(</r:mo><r:mover accent="true"><r:mi>c</r:mi><r:mo stretchy="false">¯</r:mo></r:mover><r:msub><r:mi>γ</r:mi><r:mi>μ</r:mi></r:msub><r:msub><r:mi>P</r:mi><r:mi>R</r:mi></r:msub><r:mi>b</r:mi><r:mo stretchy="false">)</r:mo></r:math>, which is present in HEFT but suppressed in SMEFT. We identify the angular observables that can have significant contributions from <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" display="inline"><bb:msubsup><bb:mi>O</bb:mi><bb:mi>V</bb:mi><bb:mrow><bb:mi>L</bb:mi><bb:mi>R</bb:mi></bb:mrow></bb:msubsup></bb:math> and hence would be useful for probing not only beyond the Standard Model physics but also physics beyond SMEFT. We further find that constraining the branching ratio of <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:msub><db:mi>B</db:mi><db:mi>c</db:mi></db:msub><db:mo stretchy="false">→</db:mo><db:mi>τ</db:mi><db:msub><db:mover accent="true"><db:mi>ν</db:mi><db:mo stretchy="false">¯</db:mo></db:mover><db:mi>τ</db:mi></db:msub></db:math> would be crucial for performing this task.