Stop Production at Hadron Colliders

TL;DR

The paper computes next-to-leading-order SUSY-QCD corrections for diagonal stop-pair production in p p̄/pp collisions at Tevatron and LHC, confirming that NLO terms stabilize theoretical predictions and typically increase cross sections, especially when gg initial states dominate. It shows that cross sections depend mainly on the produced stop masses, with mixing-angle effects entering only at higher orders, while mixed-stop production is suppressed and provides limited sensitivity to θ. The analysis uses scaling functions, threshold and high-energy behavior, and decoupling of heavy SUSY states, yielding robust predictions implemented in PROSPINO. These results enhance stop searches and enable mass determination prospects from measured cross sections at hadron colliders.

Abstract

Stop particles are expected to be the lightest squarks in supersymmetric theories and the search for these particles is an important experimental task. We therefore present the cross sections for the production processes $p\bar{p}/pp \to \ste\steb$ and $\stz\stzb$ at Tevatron and LHC energies in next-to-leading order supersymmetric QCD. The corrections stabilize the theoretical predictions for the cross sections, and they are positive, thus raising the cross sections to values above the leading-order predictions. Mixed $\ste\stzb/\steb\stz$ pairs can only be generated in higher orders at strongly suppressed rates.

Figures (5)

• Figure 1: Generic Feynman diagrams for the production of pairs of stop particles: (a) Born diagrams for quark--antiquark annihilation and gluon fusion; (b) higher-order diagrams for the diagonal production including stop mixing (dotted vertices); (c) non-diagonal production in the limit of decoupled gluinos (mixing vertices are dotted).
• Figure 2: The scaling functions for the production of $\tilde{t}_1\bar{\tilde{t}}_1$ pairs as a function of $\eta=s/4m_{\tilde{t}_{ 1}}^2-1$. The notation follows Eq. (\ref{['eq_scaling']}). The variation of the scaling function $f_{ij}^{V+S}$ for all possible values of the mixing angle $\tilde{\theta}$ is indicated by the line-thickness of the corresponding curves. The scaling functions $f_{g\bar{q}}$ are identical to $f_{qg}$.
• Figure 3: Renormalization/factorization-scale dependence of the total cross sections for $\tilde{t}_1$-pair production at the Tevatron and the LHC. The SUSY mass parameters correspond to the central values of the SUGRA-inspired scenario described in the text.
• Figure 4: The total cross sections for the production of pairs of stop particles ($\,\tilde{t}_k \bar{\tilde{t}}_k$) at the Tevatron as a function of the stop masses. The band for the NLO result indicates the uncertainty due to the renormalization/factorization scale. The light-flavor squark masses, the gluino mass and the mixing parameter are derived within the SUGRA-inspired scenario defined in the text. The line-thickness of the NLO curves represents the simultaneous variation of the gluino mass between 200 (284) and 800 GeV for $\tilde{t}_1(\tilde{t}_2)$-pair production and the variation of $\sin(2\tilde{\theta})$ over its full range.
• Figure 5: The same as Fig. \ref{['fig_sig1']}, but for the LHC. The SUSY mass spectrum is described in the text. The gluino mass is varied between 400 (600) and 900 GeV for $\tilde{t}_1(\tilde{t}_2)$-pair production.