QCD Corrections to Scalar Production via Heavy Quark Fusion at Hadron Colliders

Abstract

We recently proposed that, due to the top-quark-mass enhanced Yukawa coupling, the s-channel production of a charged scalar or pseudo-scalar from heavy quark fusion can be an important new mechanism for discovering non-standard spin-0 particles. In this work, we present the complete O(alpha_s) QCD corrections to this s-channel production process at hadron colliders, including the results of QCD resummation over multiple soft-gluon emission. The systematic QCD-improved production and decay rates at the FermiLab Tevatron and the CERN LHC are given for the charged top-pions in the topcolor models and for the charged Higgs bosons in the generic two Higgs doublet model. The direct extension to the production of the neutral (pseudo-)scalars via bb\bar fusion is studied in the minimal supersymmetric standard model (MSSM) with large tan(beta), and in the topcolor model with large bottom Yukawa coupling.

Figures (16)

• Figure 1: Representative diagrams for charged or neutral (pseudo-)scalar (dashed line) production from quark-antiquark and quark-gluon collisons at $O(\alpha_s^0)$ and $O(\alpha_s^1)$: (a) leading order contribution; (b-d) self-energy and vertex corrections (with counter term); (e) real gluon radiation in $q\bar{q}^{\prime}$-fusion; (f-g) $s$- and $t$-channel gluon-quark fusions.
• Figure 2: Estimated current $3\sigma$-bounds in the TopC model and 2HDM-III: (a) the $3\sigma$ upper bound on the top-pion Yukawa coupling ${\cal C}_R^{tb}$; (b) the $3\sigma$ lower bound on the top-pion decay constant; (Here, in (a) and (b), the solid curves are derived from the combined LEP/SLD data of $R_b^{\rm Exp}=0.21656\pm 0.00074$ while dashed curves are from the same $3\sigma$ combined experimental error but with the central $R_b$-value equal to $R_b^{\rm SM}=0.2158$.) (c) the $R_b$-predictions of 2HDM-III with coupling $\xi_{tt}=1.0$ and $1.5$ (solid curves) and the $3\sigma$$R_b$-bounds (dashed lines).
• Figure 3: Top-pion production cross sections at the present Tevatron, upgraded Tevatron, and the LHC. For each collider we show the NLO cross section with the resummed running Yukawa coupling (solid), and with one-loop Yukawa coupling (dashed), as well as the LO cross section with resummed running Yukawa coupling (dotted) and with tree-level (dash-dotted) Yukawa coupling.
• Figure 4: Cross sections for the charged top-pion production in the TopC model at the present Tevatron, upgraded Tevatron and the LHC. The NLO (solid), the $q\bar{q}'$ (dashed) and $qg$ (dash-dotted) sub-contributions, and the LO (dotted) contributions are shown. Since the $qg$ cross sections are negative, they are multiplied by $-1$ in the plot. The cross sections at $\sqrt{S} = 1.8$ TeV are multiplied by 0.1 to avoid overlap with the $\sqrt{S} = 2$ TeV curves.
• Figure 5: The $K$-factors for the $\phi^+$ production in the TopC model are shown for the NLO ($K=\sigma_{\rm NLO}/\sigma_{\rm LO}$, solid lines), $q\bar{q}'$ ($K=\sigma_{q\bar{q} '}/\sigma_{\rm LO}= (\sigma_{\rm LO}+\Delta\sigma_{q\bar{q} '})/\sigma_{\rm LO}$, dashed lines), and $qg$ ($K=-\Delta\sigma_{qg}/\sigma_{\rm LO}$, dash-dotted lines) contributions, at the upgraded Tevatron (a) and the LHC (b).