Higgs Couplings: Disentangling New Physics with Off-Shell Measurements

Abstract

After the discovery of a scalar resonance, resembling the Higgs boson, its couplings have been extensively studied via the measurement of various production and decay channels on the invariant mass peak. Recently, it has been suggested the possibility to use off-shell measurements: in particular, CMS has published results based on the highinvariant mass cross section of the process gg → ZZ, which contains the contribution of the Higgs. While this measurement has been interpreted as a constraint on the Higgs width after very specific assumptions are taken on the Higgs couplings, in this letter we show that a much more model-independent interpretation is possible.Since the discovery of a scalar boson at the LHC by the ATLAS and CMS collaborations, much effort has been devoted to the study of its properties. So far, most of the information has been obtained by extracting its couplings from the cross-section measurements in various production/decay modes on the resonance peak [1,2]. Interpreting those results in a Beyond the Standard Model (BSM) context can be easily done in terms of a handful of parameters encoding the modification of the couplings to standard particles and, among the many proposals, one has been chosen as an official recommendation by experimentalists and theorists together [3]. Recently, a novel kind of measurement has been put forward, where Higgs couplings are extracted from the cross-section integrated away from the resonance peak [4][5][6], and the first results from CMS on the H → ZZ → 4 leptons have been published [7]. This new class of measurements is most welcome, since it carries information on the Higgs couplings at a different mass scale than its mass shell, and such a dependence on the partonic centre of mass energy √ŝ is paramount to distinguishing BSM effects. Although

The Higgs legacy of the LHC Run I

“…Note that ∆ g in this representation shows a non-trivial momentum dependence, limiting the model-independent features of the width measurement [34][35][36][37][38]. If the Higgs propagator in the interference is probed far above the mass shell, it behaves like 1/s.…”

“…Finally, we include off-shell measurements of Higgs production [31][32][33] in the SFitter analysis and estimate their current impact. While it has been established that off-shell measurements will not serve as model-independent measurements of the Higgs width [34][35][36][37][38], we can establish their role in hypothesis-based Higgs studies.…”

Interplay of vector-like top partner multiplets in a realistic mixing set-up

“…These results have been discussed and relevant expressions are given in appendix E. Some salient features of the constraints are [34,59,60]:…”

Mass effects in the Higgs-gluon coupling: boosted vs. off-shell production

“…This means that the signal amplitude can be understood from the longitudinal components [78][79][80] …”

“…This way, it carries information on the Higgs couplings at different energy scales which could, similarly to the boosted case, probe the energy dependence of the higher-dimensional operators. In this spirit, we exploit the off-shell Higgs regime of ZZ production to probe the Higgs-top sector of the Standard Model [79,80].…”