Lam-Tung relation breaking in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Z</mml:mi></mml:math> boson production as a probe of standard model effective field theory effects

The violation of the Lam-Tung relation in the high-<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msubsup><a:mi>p</a:mi><a:mi>T</a:mi><a:mrow><a:mo>ℓ</a:mo><a:mo>ℓ</a:mo></a:mrow></a:msubsup></a:math> region of the Drell-Yan process at the LHC presents a longstanding discrepancy with the standard model prediction at <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi mathvariant="script">O</c:mi><c:mo stretchy="false">(</c:mo><c:msubsup><c:mi>α</c:mi><c:mi>s</c:mi><c:mn>3</c:mn></c:msubsup><c:mo stretchy="false">)</c:mo></c:math> accuracy. In this paper, we employed a model-independent analysis to investigate this phenomenon within the framework of the standard model effective field theory (SMEFT). Our findings revealed that the leading contributions from SMEFT to this violation appear at the <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mn>1</h:mn><h:mo>/</h:mo><h:msup><h:mi mathvariant="normal">Λ</h:mi><h:mn>4</h:mn></h:msup></h:math> order with <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi mathvariant="script">O</k:mi><k:mo stretchy="false">(</k:mo><k:msub><k:mi>α</k:mi><k:mi>s</k:mi></k:msub><k:mo stretchy="false">)</k:mo></k:math> accuracy in quantum chromodynamics (QCD) interaction. Notably, we demonstrated that the quadratic effect of dimension-6 dipole operators, associated with the <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mi>Z</p:mi></p:math> boson, dominates the breaking effects induced by various dimension-6 and dimension-8 operators. This provides a possible explanation for the observed discrepancy with the Standard Model predictions at the LHC. Furthermore, the breaking effects could also serve as a powerful tool for constraining <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mi>Z</r:mi></r:math>-boson dipole interactions, highlighting their importance among potential sources of new physics in the Drell-Yan process.