Off-shell effects in Higgs processes at a linear collider and implications for the LHC

Abstract

The importance of off-shell contributions is discussed for $H\to V{V}^{(\ast )}$ with $V\in \{Z,W\}$ for large invariant masses $m_{VV}$ involving a standard model (SM)-like Higgs boson with $m_H=125$GeV at a linear collider (LC). Both dominant production processes $e^{+}{e}^{-}\to ZH\to ZV{V}^{(\ast )}$ and $e^{+}{e}^{-}\to \nu \bar{\nu }H\to \nu \bar{\nu }V{V}^{(\ast )}$ are taken into account, and the signal processes are compared with background yielding the same final state. The relative size of the off-shell contributions is strongly dependent on the centre-of-mass energy. These contributions can have an important impact on the determination of cross sections and branching ratios. However, the combination of on- and off-shell contributions can also be utilised to lift degeneracies allowing to test higher-dimensional operators, unitarity and light and heavy Higgs interferences in extended Higgs sectors. The latter is demonstrated in the context of a 2-Higgs-Doublet model. We also discuss the impact of these aspects for the Large Hadron Collider (LHC) where they are relevant. The importance of a precise measurement of the Higgs mass for on-shell contributions in $H\to V{V}^{(\ast )}$ is emphasized. A particular focus is put on methods for extracting the Higgs width at a LC. Off-shell contributions are shown to have a negligible impact on the width determination at low $\sqrt{s}$ when applying the $Z$ recoil method to extract branching ratios in combination with an appropriate determination of a partial width. On the other hand, off-shell contributions can be exploited to constrain the Higgs width in a similar fashion as in recent analyses at the LHC. It is demonstrated that this approach, besides relying heavily on theoretical assumptions, is affected by the negative interference of Higgs and background contributions that may limit the sensitivity that is achievable with the highest foreseeable statistics at the LHC and a LC.

33 pages, 15 figures; minor clarifications, updated references, matches published version

References in corpus (28)

• Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC
• Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC
• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• MadAnalysis 5, a user-friendly framework for collider phenomenology
• Models of Yukawa interaction in the two Higgs doublet model, and their collider phenomenology
• The complex-mass scheme for perturbative calculations with unstable particles
• Constraints on the Higgs boson width from off-shell production and decay to Z-boson pairs
• Mass Effects in the Higgs-Gluon Coupling: Boosted vs Off-Shell Production
• LHC HXSWG interim recommendations to explore the coupling structure of a Higgs-like particle
• Limitations and Opportunities of Off-Shell Coupling Measurements
• Higgs Pseudo-Observables, Second Riemann Sheet and All That
• Taming the off-shell Higgs boson
• Beyond Geolocating: Constraining Higher Dimensional Operators in $H\to 4\ell$ with Off-Shell Production and More
• Two-Loop Renormalization in the Standard Model Part III: Renormalization Equations and their Solutions
• Higgs couplings: disentangling New Physics with off-shell measurements
• Jet Vetoes Interfering with H->WW
• Interference effects for Higgs-mediated Z-pair plus jet production
• Higgs constraints from vector boson fusion and scattering
• On-shell interference effects in Higgs final states
• Bounding the Higgs Width Using Effective Field Theory
• Off-Shell Higgs Coupling Measurements in BSM scenarios
• Model Independent Determination of $HWW$ coupling and Higgs total width at ILC
• Study of Higgs-gauge boson anomalous couplings through $e^{-}{e}^{+}\to W^{-}{W}^{+}H$ at ILC
• Bounding the Higgs width at the LHC
• Unitarity in composite Higgs approaches with vector resonances
• Higgs Recoil Mass and Higgs-Strahlung Cross-Section Study for the ILD LOI
• Precision Measurements of SM Higgs Recoil Mass and Cross Section for Ecm of 230 GeV and 250 GeV at ILC
• Interference effects in Heavy Higgs production via gluon fusion in the Singlet Extension of the Standard Model

Cited by in corpus (2)

• Improving Higgs coupling measurements through ZZ Fusion at the ILC
• Off-shell effects in Higgs decays to heavy gauge bosons and signal-background interference in Higgs decays to photons at a linear collider