Top Pair Production at Hadron Colliders in non-minimal Standard Models

TL;DR

Top-quark pair production at hadron colliders is analyzed beyond the Standard Model by computing $\mathcal{O}(\alpha\alpha_s^2)$ electroweak-like corrections in the General 2-Higgs-Doublet Model and the MSSM for the $q\bar q$ and $gg$ channels. The approach provides analytic form factors for the corrected $gt\overline{t}$ vertex and evaluates the impact after convolution with parton distributions, revealing large parton-level effects near threshold (up to ~$50\%$) but modest hadron-level reductions (a few percent) in most of parameter space; sizeable enhancements occur only in special threshold regions involving $t\to b H^+$ or stop/neutralino thresholds. Distinctive signatures arise in the gluon-fusion channel from $s$-channel Higgs exchange, potentially distorting the $M_{t\overline{t}}$ distribution at the LHC if the Higgs width is small and $M_{H^0}>2 m_t$. The results indicate that, with reduced QCD uncertainties, these electroweak effects in top production could provide valuable probes of the Higgs sector and SUSY dynamics at future hadron colliders.

Abstract

The cross section of top pair production in hadronic collisions to O(alpha α_s^2) is calculated within the General 2-Higgs-Doublet Model and the Minimal Supersymmetric Standard Model. At the parton level the O(alpha) one-loop corrections to the main production mechanisms, quark-antiquark annihilation and gluon fusion, significantly modify the Born-cross sections: in the threshold region \sqrt{\hat s}>~2 m_t they are enhanced up to 50 % and with increasing cm energy \sqrt{\hat s}, they can be reduced by up to the same order of magnitude. In a wide range of the parameter space of the models under consideration the observable hadronic cross sections for top pair production at the Tevatron and at the LHC are typically reduced by several percent (<~10 %) compared to the lowest order result. In special regions of the parameter space, that is in the vicinity of the threshold for the top quark decay t \to b H^+ ; \tilde t \tilde χ^0, the radiative corrections are considerably enhanced, comparable in size to QCD effects.

Figures (20)

• Figure 1: The relative corrections $\Delta_{q\overline{q}}$ and $\Delta_{gg}$ within the MSM. The ${\cal O}(\alpha)$ contribution of the electroweak gauge bosons (dotted line) and of the Higgs-sector are shown separately (solid line: $M_H=65$ GeV, dashed line: $M_H=1$ TeV).
• Figure 2: The Feynman-rules for the $H$-$t$-$t(b)$-vertex within the 2-Higgs-Doublet Model written in generalized form. The coupling parameters $c_s,c_p,c_p'$ are explicitly given in Tab. I.
• Figure 3: The variation of the relative corrections $\Delta_{q\overline{q}}$ and $\Delta_{gg}$ with $M_{H^0}$ and $\tan{\beta}$ within the G2HDM (with $M_{h^0}=45$ GeV, $M_{A^0}=50$ GeV, $M_{H^\pm}=50$ GeV and $\alpha=\pi/2$).
• Figure 4: The Feynman-diagrams for the SUSY EW-like contributions to the $\hbox{$q\overline{q}$ annihilation}$ subprocess.
• Figure 5: The Feynman-diagrams for the SUSY EW-like contributions to the gluon fusion subprocess.