Associated Production of a Top Quark and a Charged Higgs Boson

TL;DR

The paper delivers a comprehensive NLO QCD and SUSY-QCD analysis of the associated production of a top quark and a charged Higgs boson ($pp\to tH^-+X$) at hadron colliders. It employs a bottom-quark parton density and a two-cutoff phase-space slicing method to produce fully differential predictions, while matching to gluon-initiated and off-shell top-pair channels to cover the full $m_H$ range. At the LHC, the predicted cross section experiences a $K$-factor of about $K\sim 1.4$ with reduced scale uncertainties, and differential distributions remain stable under NLO corrections; SUSY contributions, especially the $\Delta_b$ renormalizations, can be sizeable for large $\tan\beta$ but often remain within the perturbative uncertainties. The work provides robust benchmarks for charged-Higgs searches in the MSSM and clarifies the interplay between bottom-parton and gluon-initiated production mechanisms across mass regimes.

Abstract

We compute the inclusive and differential cross sections for the associated production of a top quark along with a charged Higgs boson at hadron colliders to next-to-leading order (NLO) in perturbative quantum chromodynamics (QCD) and in supersymmetric QCD. For small Higgs boson masses we include top quark pair production diagrams with subsequent top quark decay into a bottom quark and a charged Higgs boson. We compare the NLO differential cross sections obtained in the bottom parton picture with those for the gluon-initiated production process and find good agreement. The effects of supersymmetric loop contributions are explored. Only the corrections to the Yukawa coupling are sizable in the potential discovery region at the CERN Large Hadron Collider (LHC). All expressions and numerical results are fully differential, permitting selections on the momenta of both the top quark and the charged Higgs boson.

Figures (11)

• Figure 1: The leading order Feynman diagrams for the production process $gb \to t H^-$. We indicate how the bottom partons are created through gluon splitting.
• Figure 2: Cross section dependence on the cutoff parameters $\delta_c$ and $\delta_s$ at the LHC energy. Left: The soft cutoff $\delta_s$ is fixed to different values. Right: two dimensional logarithmic dependence on both cutoff parameters.
• Figure 3: The scale variation of the cross sections at the LHC for $m_H=250{\;\rm GeV}$ and $\tan\beta=30$. The central values are $\mu_R^0=M/2$ and $\mu_F^0=M/5$. The four panels show the leading order cross section, the complete NLO cross section, the $gb$ induced NLO cross section and the $gg$ induced contribution to the NLO cross section.
• Figure 4: Left: The $tH^-$ inclusive cross section at the LHC as a function of $\tan\beta$. The solid curve is the NLO result, with the scale variations around the central scale $\mu/\mu_0=1/4-4$ indicated by the thinner solid curves. Also shown are the leading order result with a running bottom quark Yukawa coupling (dashed curve) as well as a pole mass Yukawa coupling (dotted curve). Right: The total cross section at the LHC as a function of the charged Higgs boson mass as the solid curve. The NLO and LO cross sections are shown as the dashed upper and lower curves, respectively. The dotted curves show the cross sections for $pp \to t \bar{t}^*+X$ with a subsequent decay $\bar{t}^* \to \bar{b} H^-$ in the Breit-Wigner approximation $(\sigma_{\rm BW})$ and that including the complete set of off-shell diagrams $(\sigma_{\rm off-shell})$.
• Figure 5: The cross section for the Tevatron ($2{\;\rm TeV}$) as a function of the charged Higgs boson mass. We also show the cross sections for $pp \to t \bar{t}^* + X$ with a subsequent decay $\bar{t}^* \to \bar{b} H^-$ in the Breit--Wigner approximation and including the complete set of off-shell diagrams.