Taming the off-shell Higgs boson

TL;DR

The paper uses an EFT framework to exploit off-shell Higgs production in $pp\to h^{(*)}\to ZZ^{(*)}\to 4\ell$ as a probe of energy-dependent Higgs couplings, aiming to disentangle long- and short-distance contributions to the gluon fusion vertex and to constrain the top Yukawa coupling. It develops a method to relate the differential off-shell cross section to dimension-6 operators, assesses current 8 TeV data, and provides projections for HL-LHC and FCC-hh including top-partner and CP-odd scenarios. The results show that current data offer limited model-independent bounds, but future hadron colliders can substantially tighten constraints on $c_t$ and $c_g$, with the off-shell channel helping to break degeneracies inherent in on-shell measurements. The work also discusses theoretical uncertainties, the role of dimension-8 operators, and the status of QCD corrections for gg→ZZ, highlighting the potential for off-shell Higgs studies to probe new physics in the Higgs sector.

Abstract

We study the off-shell Higgs data in the process $pp\to h^{(*)} \to Z^{(\ast)}Z^{(\ast)}\to 4\ell$, to constrain deviations of the Higgs couplings. We point out that this channel can be used to resolve the long- and short-distance contributions to Higgs production by gluon fusion and can thus be complementary to $pp\to ht\bar t$ in measuring the top Yukawa coupling. Our analysis, performed in the context of Effective Field Theory, shows that current data do not allow one to draw any model-independent conclusions. We study the prospects at future hadron colliders, including the high-luminosity LHC and accelerators with higher-energy, up to 100 TeV. The available QCD calculations and the theoretical uncertainties affecting our analysis are also briefly discussed.

Figures (7)

• Figure 1: Sample diagrams contributing to $gg\rightarrow ZZ$.
• Figure 2: $68\%,95\%$ and $99\%$ probability contours in the $c_t$,$c_g$ plane, using the 8 TeV CMS data set. A 10% systematic uncertainty was assumed on the $q\bar{q}$ background.
• Figure 3: Posterior probability as a function of $c_t$, assuming the constraint $c_t+c_g=1$, for the 8 TeV CMS data set. At $95\%$ we find $c_t\in[-4.7,0.5]\cup[1, 6.7]$ (unshaded region), at $68\%$$c_t\in [-4,-1.5]\cup[2.9,6.1]$. The red line shows the expected probability for the SM signal.
• Figure 4: Prospects for a 14 TeV analysis with an integrated luminosity of 3 ab${}^{-1}$ and for the injected SM signal: $68\%,95\%$ and $99\%$ expected probability regions in the $(c_t,c_g)$ plane. The dashed and solid green lines indicate the $68\%$ and $95\%$ contours for the linear analysis, respectively. No theoretical uncertainty is included.
• Figure 5: Prospects for the 14 TeV analysis with an integrated luminosity of 3 ab${}^{-1}$ and for the injected SM signal: expected posterior probability as a function of $c_t$, assuming the constraint $c_t+c_g=1$ and to observe the SM signal. The black curve corresponds to the nonlinear analysis including all bins, at 95$\%$ probability we find $c_t\in[0.56,1.46]$ (unshaded region), at 68$\%$$c_t\in[0.74,1.28]$. The red curve was obtained using only the categories below $600$ GeV and at $68\%$ we have $c_t\in[0.1,1.25]$. The brown curve corresponds to the linear analysis including all bins, which gives $c_t\in[0.36,1.66]$ at $68\%$.