Enhanced Supersymmetric Corrections to Top-Quark Production at the Tevatron

TL;DR

This work evaluates one-loop supersymmetric corrections to top-quark pair production at the Tevatron, treating both electroweak-like (top/bottom squark and neutralino/chargino loops) and QCD-like (gluino/squark loops) contributions with non-degenerate stop masses and left-right mixing. The authors derive analytic expressions for the corrections, including detailed form factors and Passarino–Veltman functions, and explore parameter regions where enhancements occur. Numerically, electroweak-like corrections can yield large negative shifts up to about $-35\%$ near thresholds, while QCD-like corrections can yield positive shifts up to about $+20\%$ for light sparticles, with a general decoupling trend for heavier masses. They discuss implications for MSSM scenarios aimed at experimental anomalies (e.g., R_b, light higgsino window, Kane–Mrenna) and note potential effects on top-quark decays, highlighting the relevance of precision top-quark measurements as probes of low-energy supersymmetry.

Abstract

We calculate the one-loop supersymmetric electroweak-like and QCD-like corrections to the top-quark pair-production cross section at the Tevatron, including the important effects of non-degenerate top-squarks and left-right top-squark mixing. The largest electroweak effects yield a negative shift in the cross section and are enhanced right below the threshold for top-quark decay into top-squark and higgsino-like neutralino, and can be as large as $-35\%$. The largest QCD effects are positive and are enhanced for light top-squark masses, and can be as large as $20\%$. Such shifts greatly exceed the present theoretical uncertainty in the Standard Model prediction, and therefore may be experimentally observable. We also explore the one-loop shifts in scenarios containing light top-squarks and higgsino-like neutralinos that have been recently proposed to explain various apparent experimental anomalies.

Figures (8)

• Figure 1: Tree-level diagram (a) describing $q\bar{q}\to t\bar{t}$ production. The blob diagram (b) indicates the choice of external momenta used throughout our calculations.
• Figure 2: Feynman diagrams describing the one-loop supersymmetric electroweak-like corrections to $q\bar{q}\to t\bar{t}$, including external leg corrections (a,b) and vertex corrections (c) from top-squark and neutralino loops. An analogous set of diagrams exists where the top-squarks are replaced by bottom-squarks and the neutralinos by charginos.
• Figure 3: Feynman diagrams describing the one-loop supersymmetric QCD-like corrections to $q\bar{q}\to t\bar{t}$, including external leg corrections (a,b,e,f), vertex corrections (c,d,g,h), and a representative box diagram (i).
• Figure 4: Representative box diagram (one of four possible ones) describing the mixed one-loop supersymmetric QCD-like and electroweak-like corrections.
• Figure 5: The relative (%) one-loop supersymmetric electroweak-like correction to the top-quark pair-production cross section at the Tevatron as a function of the (higgsino-like) neutralino mass, for $m_t=175\,{\rm GeV}$, $\tan\beta=1$, $m_{\tilde{t}_1}=50\,{\rm GeV}$, $m_{\tilde{t}_2}=100\,{\rm GeV}$, and various choices of the top-squark mixing angle ($\theta_t=0.0,0.10,0.25,{\pi\over4}$). The dotted curve on the upper-left-hand panel corresponds to $m_{\tilde{t}_1}=m_{\tilde{t}_2}=50\,{\rm GeV}$. Note the dips on the curves when $m_t\approx m_{\tilde{t}_{1,2}}+m_\chi$.