Gluino Pair Production at the LHC: The Threshold

TL;DR

The paper investigates gluino-pair production near threshold at the LHC within SUSY QCD, employing non-relativistic QCD and a Green's-function formalism to capture threshold enhancements from final-state interactions. It separates the calculation into Green's-function (threshold) and short-distance (hard) NLO corrections, addressing all relevant colour configurations and implementing an \,DR-\bar scheme for SUSY QCD. The authors provide detailed, colour- and spin-resolved results for the differential cross section as a function of the gluino-pair invariant mass, demonstrating a consistent 7–9% enhancement over fixed-order predictions and improved scale stability across multiple SUSY benchmark scenarios. These findings refine predictions for gluino searches at the LHC, particularly in regions where bound-state effects or strong final-state interactions influence the threshold behaviour, and remain applicable as squark and gluino masses vary.

Abstract

The next-to-leading order analysis of the cross section of hadronic gluino pair production 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 remnant of the 1S peak below the nominal pair threshold. This enhancement is similar to the corresponding one for top production. However, as a consequence of the larger colour factor of the QCD potential the effect is significantly enhanced. The analysis includes all colour configurations of S-wave gluino pairs, i.e. singlet, symmetric and antisymmetric octet, decuplet and twenty-seven representation. Matching coefficients involving real and virtual radiation are separately evaluated for all colour and spin configurations and initial states. We concentrate on the case of gluino decay rates comparable to the gluino binding energy. The non-relativistic dynamics of the gluino pair is solved by calculating the Green's function in NLO. Numerical results for the Large Hadron Collider at sqrt(s)=14 TeV and 7 TeV are presented for various characteristic scenarios.

Figures (22)

• Figure 1: Level spacing $\Delta M$ and annihilation rates $\Gamma_{gg}$ (solid curves) compared to the gluino decay rates $2\Gamma_{\tilde{g}}$. Fig. (a): for three different squark masses (dashed: $0.5\,\hbox{TeV}$, dash-dotted: $1\,\hbox{TeV}$, dotted: $1.5\,\hbox{TeV}$). Fig. (b): for fixed ratios ($\rho=m_{\tilde{g}}/m_{\tilde{q}}$) between squark and gluino masses. Fig. (c): for the benchmark points (see Tab. \ref{['SPSmain']}).
• Figure 2: Feynman diagrams contributing at LO to $gg\rightarrow\tilde{g}\tilde{g}$ and $q\overline{q}\rightarrow\tilde{g}\tilde{g}$.
• Figure 3: Imaginary part of the Green's functions for benchmark points (p), (a) and (q) for the singlet (dashed), octet (dash-dotted), decuplet (solid) and twenty-seven configuration (dotted). For the decuplet we show the free Green's function. LO and NLO curves for twenty-seven lie on top of each other.
• Figure 4: LO prediction for the invariant mass distribution for scenario (p).
• Figure 5: NLO contributions to the $gg$ initiated processes without virtual squarks (dotted lines correspond to ghost fields).