SUSY QCD one-loop effects in (un)polarized top-pair production at hadron colliders

TL;DR

This study provides a complete computation of SUSY QCD one-loop corrections to strong tt̄ production at hadron colliders, covering both qq̄ annihilation and gg fusion in the MSSM and addressing polarized and unpolarized observables. By implementing a SUSY-decoupled renormalization scheme and detailing the scalar top sector, the authors quantify how gluinos, stops, and squarks influence total cross sections and kinematic distributions at Tevatron and LHC, including threshold effects at gluino-pair production. They find that corrections can reach several percent for integrated hadronic cross sections and can distort M_tt and p_T distributions notably near thresholds, while polarization-sensitive observables at the LHC show potential signals up to a few percent in left-right asymmetries and up to several percent in spin correlations. The work demonstrates the phenomenological relevance of SQCD loop effects for top-quark precision studies and provides analytic results, cross-checks, and Fortran tools to facilitate future collider analyses, with caveats about decays and detector responses. Overall, the paper assesses the viability of observing SUSY loop effects in tt̄ production and highlights parameter regions where such effects are enhanced at the LHC.

Abstract

We study the effects of O(alpha_s) supersymmetric QCD (SQCD) corrections on the total production rate and kinematic distributions of polarized and unpolarized top-pair production in pp and p anti-p collisions. At the Fermilab Tevatron p anti-p collider, top-quark pairs are mainly produced via quark-antiquark annihilation, q anti-q -> t anti-t, while at the CERN LHC pp collider gluon-gluon scattering, g g -> t anti-t, dominates. We compute the complete set of O(alpha_s) SQCD corrections to both production channels and study their dependence on the parameters of the Minimal Supersymmetric Standard Model. In particular, we discuss the prospects for observing strong, loop-induced SUSY effects in top-pair production at the Tevatron Run II and the LHC.

Figures (29)

• Figure 1: Feynman diagram to the $q\overline{q} \to t\overline{t}$ subprocess at LO QCD.
• Figure 2: Feynman diagrams to the $s$ (diagram (a)), $t$ (diagram (b)) and $u$ (diagram(c)) channels of the $gg \to t\overline{t}$ subprocess at LO QCD.
• Figure 3: Generic self-energy (diagram (a)) and vertex (diagrams (b) and (c)) corrections to $q\overline{q} \to t\overline{t}$ at NLO SQCD. The corrections to the gluon propagator and the $gq\bar{q}$ vertex are explicitly shown in Figs. \ref{['fig:gself_renorm']} and \ref{['fig:gtt_renorm']}, respectively.
• Figure 4: (a) Direct box diagram and (b) crossed box diagram contributing to $q\overline{q}\to t\overline{t}$ at NLO SQCD. Graphs containing squarks/stops are summed over the squark/stop mass eigenstates i,j=L,R (no mixing), i,j=1,2 (with mixing).
• Figure 5: Generic vertex and self-energy corrections to the $t(u)$ channel (diagrams (a)-(c)) and the $s$ channel (lower row) of the $gg \to t\overline{t}$ subprocess at NLO SQCD. The corrections to the $gt\bar{t}$ vertex, the quark and gluon propagators, and the $ggg$ vertex are explicitly shown in Figs. \ref{['fig:gtt_renorm']}, \ref{['fig:qself_renorm']}, \ref{['fig:gself_renorm']}, and \ref{['fig:ggg_renorm']}, respectively.