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

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.

Figures (10)

• Figure 1: Contribution to $Zh$ production via gluon fusion to a pseudoscalar at LHC, for $m_A$ = 95 GeV, as a function of $\tan\beta$. The cross section is computed at NNLO.
• Figure 2: Contribution to $Zh$ production via gluon fusion to a pseudoscalar at LHC within the 2HDMS type II, for $m_{a_1} = 95 \,\, \mathrm{GeV}$, as a function of the lightest pseudoscalar top coupling modifer $c_{a_1 tt}$ The cross section is computed at NNLO (see text).
• Figure 3: The cross section for $gg \to A \to Zh$ as a function of $m_A$ in the 2HDM type I for $\sqrt{s} = 13$ TeV and for several values of $m_H = m_{H^\pm}$ (see color coding). The other parameters are $\tan\beta = 1$, $\cos(\beta - \alpha) = 0.1$.
• Figure 4: Scatter plots for the parameter space of the 2HDM type I (see text). (a) NNLO Cross section for $gg\to A\to Zh$ as a function of $m_A$. The solid/dashed red (green) line is the current lower $2\,\sigma$/$1\,\sigma$ limit on $Zh$ production from LHC (HL-LHC). The black line corresponds to the current limits of the $gg\to A \to Zh$ cross section from CMS. (b) $\tan\beta$ vs. $\cos(\beta - \alpha)$: red points indicate those regions of parameter space above the $2\,\sigma$ solid red line, but below the CMS exclusion in the left plot; orange points indicate those regions of parameter space above the CMS exclusion limit in the left plot.
• Figure 5: Scatter plots for the parameter space of the 2HDM type II (see text). (a) NNLO Cross section for $gg\to A\to Zh$ as a function of $m_A$. The solid/dashed red (green) line is the current lower $2\,\sigma$/$1\,\sigma$ limit on $Zh$ production from LHC (HL-LHC). The black line correspnds to the current limits of the $gg\to A \to Zh$ cross section from CMS. (b) $\tan\beta$ vs. $\cos(\beta - \alpha)$: red points indicate those regions of parameter space above the $2\,\sigma$ solid red line, but below the CMS exclusion in the left plot; orange points indicate those regions of parameter space above the CMS exclusion limit in the left plot.