Gluino-Squark Production at the LHC: The Threshold

TL;DR

This work analyzes gluino-squark production near threshold at the LHC using a non-relativistic QCD framework to capture final-state interactions across colour-S-wave states ${\mathbf3}$, ${\mathbf{6}}$, and ${\mathbf{15}}$. The cross section is computed from a short-distance hard kernel augmented by the imaginary part of a Green's function evaluated at the origin, with the Green's function solved to NLO in a Coulomb-like potential and the hard part corrected by leading logarithms from initial- and final-state radiation. Using SPS-based benchmark points, the study finds that final-state interactions enhance the total cross section by about 2–3% and distort the invariant-mass distribution near threshold, especially for the attractive triplet channel, while sharp resonances are suppressed by constituent decay widths. The results provide quantitative predictions for LHC energies and illustrate how threshold dynamics modulate the gluino-squark signature in proton collisions.

Abstract

An analysis of the cross section for hadronic production of gluino-squark pairs close to threshold is presented. Within the framework of non-relativistic QCD a significant enhancement compared to fixed order perturbation theory is observed which originates from the characteristic remnants of the gluino-squark resonances below the nominal pair threshold. The analysis includes all colour configurations of S-wave gluino-squark pairs, i.e. triplet, sextet and 15 representation. Matching coefficients at leading order are separately evaluated for all colour configurations. The dominant QCD corrections, arising from initial- and final-state radiation are included. The non-relativistic dynamics of the gluino pair is solved by calculating the Green's function in Next-to-Leading Order (NLO). The results are applied to benchmark scenarios, based on Snowmass Points and Slopes (SPS). As a consequence of the large decay rate of at least one of the constituents squark or gluino annihilation decays of the bound state (\tilde{g}\tilde{q})\rightarrow gq, qγ, qZ or q'W^{\pm} are irrelevant. Thus the signatures of gluino-quark production below and above the nominal threshold are identical. Numerical results for the cross section at the Large Hadron Collider (LHC) at \sqrt{s}=7 TeV and 14 TeV are presented. The enhancement of the total cross section through final state interaction amounts to roughly 3%.

Figures (9)

• Figure 1: Feynman diagrams contributing at LO to $\tilde{g}\tilde{q}\rightarrow gq$.
• Figure 2: Feynman diagrams contributing at LO to $\tilde{g}\tilde{q}\rightarrow \gamma q,Zq,W^{\pm}q'$.
• Figure 3: Imaginary part of the Green's function for scenario (p) for the up-type (at the top) and the down-type (at the bottom) squarks. LO and NLO curves are plotted for all three colour configurations, whereas both curves lie on top of each other for the ${\bf 15}$ representation.
• Figure 4: Prediction for the invariant mass distribution for scenario (p) at LO. The upper four plots represent the results for the configurations separately and are ordered as in Fig. \ref{['fig:Green']}. The figure at the bottom displays the individual contributions from $\tilde{u}_{L,R}$ and $\tilde{d}_{L,R}$ and their sum.
• Figure 5: Prediction for differential cross section as function of the invariant mass for scenario (p) evaluated in NLO approximation as defined in Eqs. (\ref{['eqn:FnloSG']}) and (\ref{['eqn:FnloSG2']}) for the four squark species. Also shown is the sum of the four squarks (solid curve) and the FO prediction (long dashed curve).