Pseudoscalar contributions to Zh production at the LHC at 95 GeV and above

TL;DR

This paper investigates how pseudoscalar particles in extended scalar models influence Zh production at the LHC, especially around 95 GeV and up to 1000 GeV, with implications for current experimental constraints.

Contribution

It provides detailed calculations of cross sections for pseudoscalar contributions in two models, analyzing their impact on LHC measurements and parameter space constraints.

Findings

Pseudoscalar at 95 GeV has negligible effect on Zh production.

Heavier pseudoscalars can significantly increase Zh cross sections.

Current LHC data constrains the parameter space of extended scalar models.

Abstract

In generalizations of the Standard Models with extended scalar sectors, pseudoscalar particles will contribute to associated production of the Higgs boson discovered at the LHC, $h$, and the $Z$ boson. The pseudoscalar can be produced via gluon-gluon fusion, and as such may give contributions to $Zh$ production comparable to the value predicted by the Standard Model. We analyze this possibility in two different models, the Two Higgs Doublet Model, with and without an added complex singlet scalar, computing both the total and differential cross sections for this process. We focus on two pseudoscalar mass regions: (i) $m_A \sim 95$ GeV, to describe the di-photon excesses observed by CMS and ATLAS; (ii) 100 GeV $ \le m_A \le $ 1000 GeV, as a generic heavier pseudoscalar. A pseudoscalar with $m_A \sim 95$ GeV tends to give a contribution to the $pp \to Zh$ cross section that is too small to set new limits on the parameter spaces of the two models. Heavier pseudoscalars, on the other hand, can yield cross-section contributions larger than allowed by current LHC measurements and thus restricting regions of parameter space of these models which are in agreement with theoretical and all other experimental constraints. The increase of LHC luminosity will yield even substantially tighter constraints.