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Charming the Higgs

Cédric Delaunay, Tobias Golling, Gilad Perez, Yotam Soreq

TL;DR

This work shows that Higgs data permit a sizable enhancement of the Higgs–charm coupling $c_c$, potentially making $h\to c\bar{c}$ competitive with $h\to b\bar{b}$ without new production mechanisms. Using a global EFT-based fit and considering charm-loop and charm-fusion contributions to production, the authors derive 95.4% CL bounds such that $c_c$ can be as large as about 4 if gluon-fusion is correspondingly enhanced. They demonstrate that a larger $c_c$ suppresses the $h\to b\bar{b}$ signal in vector-boson associated production, but this loss can be partly recovered by charm-tagging, enabling $\mu_{b\bar{b}+c\bar{c}}$ to remain near the SM value. The paper also discusses theoretical realizations of enhanced $c_c$ in EFT, MFV/GMFV 2HDMs, and composite Higgs scenarios, showing that mild cancellations among $\mathcal{O}(1)$ coefficients can yield sizeable charm couplings while preserving consistency with existing data. Overall, the results highlight a viable path to substantial modifications of Higgs phenomenology through the charm sector, with practical implications for LHC analyses and new-physics model building.

Abstract

We show that current Higgs data permit a significantly enhanced Higgs coupling to charm pairs, comparable to the Higgs to bottom pairs coupling in the Standard Model, without resorting to additional new physics sources in Higgs production. With a mild level of the latter current data even allow for the Higgs to charm pairs to be the dominant decay channel. An immediate consequence of such a large charm coupling is a significant reduction of the Higgs signal strengths into the known final states as in particular into bottom pairs. This might reduce the visible vector-boson associated Higgs production rate to a level that could compromise the prospects of ever observing it. We however demonstrate that a significant fraction of this reduced signal can be recovered by jet-flavor-tagging targeted towards charm-flavored jets. Finally we argue that an enhanced Higgs to charm pairs coupling can be obtained in various new physics scenarios in the presence of only a mild accidental cancellation between various contributions.

Charming the Higgs

TL;DR

This work shows that Higgs data permit a sizable enhancement of the Higgs–charm coupling , potentially making competitive with without new production mechanisms. Using a global EFT-based fit and considering charm-loop and charm-fusion contributions to production, the authors derive 95.4% CL bounds such that can be as large as about 4 if gluon-fusion is correspondingly enhanced. They demonstrate that a larger suppresses the signal in vector-boson associated production, but this loss can be partly recovered by charm-tagging, enabling to remain near the SM value. The paper also discusses theoretical realizations of enhanced in EFT, MFV/GMFV 2HDMs, and composite Higgs scenarios, showing that mild cancellations among coefficients can yield sizeable charm couplings while preserving consistency with existing data. Overall, the results highlight a viable path to substantial modifications of Higgs phenomenology through the charm sector, with practical implications for LHC analyses and new-physics model building.

Abstract

We show that current Higgs data permit a significantly enhanced Higgs coupling to charm pairs, comparable to the Higgs to bottom pairs coupling in the Standard Model, without resorting to additional new physics sources in Higgs production. With a mild level of the latter current data even allow for the Higgs to charm pairs to be the dominant decay channel. An immediate consequence of such a large charm coupling is a significant reduction of the Higgs signal strengths into the known final states as in particular into bottom pairs. This might reduce the visible vector-boson associated Higgs production rate to a level that could compromise the prospects of ever observing it. We however demonstrate that a significant fraction of this reduced signal can be recovered by jet-flavor-tagging targeted towards charm-flavored jets. Finally we argue that an enhanced Higgs to charm pairs coupling can be obtained in various new physics scenarios in the presence of only a mild accidental cancellation between various contributions.

Paper Structure

This paper contains 7 sections, 28 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Constraints from Higgs data
  3. Observability of $h\to c\bar{c}$ at the LHC
  4. Charm coupling beyond the SM
  5. Conclusions
  6. Unconstrained Higgs fit
  7. Higgs couplings in GMFV

Figures (3)

  • Figure 1: $\delta\chi^2=\chi^2-\chi^2_{\rm min}$ as a function of the Higgs to charm pairs coupling $c_c$. The black and red curves correspond respectively to case (a), where all Higgs coupling but $c_c$ are SM-like, and case (b), where only $c_c$ and $c_{gg}$ deviate from the SM and marginalizing over the latter. Horizontal dashed lines denotes the $68.3\%$ and $95.4\%$ CL ($\delta\chi^2=1$ and $4$, respectively).
  • Figure 2: $68.3\%$ (solid) and $95.4\%$ (dashed) CL regions in the $c_c-c_{gg}$ plane in case (b) where only the Higgs to charm and Higgs to gluon couplings are allowed to deviate from their SM values. The red dot represents the best fit point. $\hat{c}_{gg}^{\rm SM}\simeq 0.012\,$.
  • Figure 3: Correlation between $\mu_{c\bar{c}}$ and $\mu_{b\bar{b}}$ signal strengths in the presence of an enhance Higgs to charm coupling relative the SM. Relative weights of each Higgs production mechanisms from the CMS analysis CMS_VHbb are assumed for both signal strengths. The red dot represents the best fit point and the solid (dashed) black line is the $68.3\, (95.4)\%$ CL contour derived from fitting current Higgs data for case (b), where only $c_c$ and $c_{gg}$ are not SM-like. The solid (dashed) gray contour delineates the allowed $68.3\,(95.4)\%$ CL region for the more general case where $c_b$ is allowed to vary as well.