<p>Motivated by a small but intriguing excess observed in the decay mode <i>H</i> → <i>ℓ</i><sup>+</sup><i>ℓ</i><sup><i>−</i></sup><i>γ</i> reported by both the ATLAS and CMS collaborations, we explore the possibility that new physics contributes directly to the effective <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13130_2025_26359_Article_IEq1.gif" Format="GIF" Height="22" Rendition="HTML" Resolution="72" Type="Linedraw" Width="45" /> </InlineMediaObject> <EquationSource Format="MATHML"><math display="inline"> <mi>H</mi> <mover accent="true"> <mi mathvariant="script">ll</mi> <mo stretchy="true">¯</mo> </mover> <mi>γ</mi> </math></EquationSource> <EquationSource Format="TEX">\( H\overline{\mathcal{ll}}\gamma \)</EquationSource> </InlineEquation> coupling rather than modifying the <i>Z</i> peak. Concretely, we consider a dimension-8 operator that could arise from new particles via box diagrams. Such non-resonant contribution may provide an alternative origin for current or future excesses. We examine how experimental cuts may distinguish between possible modifications of the <i>Z</i> peak and non-resonant contributions. The currently measured excess requires that the new physics scale is relatively low (Λ<sub><i>R</i></sub> ~ <i>v</i>). However, we show that it may remain within current experimental bounds. In particular, we illustrate this using a simplified model, motivated by the dark matter problem, and discuss its other experimental constraints.</p>

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On new physics off the Z peak in H → ℓ+γ

  • Aliaksei Kachanovich,
  • Jean Kimus,
  • Steven Lowette,
  • Michel H. G. Tytgat

摘要

Motivated by a small but intriguing excess observed in the decay mode H+γ reported by both the ATLAS and CMS collaborations, we explore the possibility that new physics contributes directly to the effective H ll ¯ γ \( H\overline{\mathcal{ll}}\gamma \) coupling rather than modifying the Z peak. Concretely, we consider a dimension-8 operator that could arise from new particles via box diagrams. Such non-resonant contribution may provide an alternative origin for current or future excesses. We examine how experimental cuts may distinguish between possible modifications of the Z peak and non-resonant contributions. The currently measured excess requires that the new physics scale is relatively low (ΛR ~ v). However, we show that it may remain within current experimental bounds. In particular, we illustrate this using a simplified model, motivated by the dark matter problem, and discuss its other experimental constraints.