Weak boson fusion production of supersymmetric particles at the LHC

TL;DR

The study tackles the challenge of predicting weak boson fusion production of colorless MSSM particles at the LHC, addressing unitarity constraints and SLHA input ambiguities. It develops SUSY-MadGraph to generate MSSM processes with Majorana fermions, derives unitarity sum rules for VV→χχ, and enforces a consistent SLHA-based treatment of electroweak inputs. Across MSSM benchmark points, most WBF cross sections are at the attobarn level, with a few notable exceptions such as χ^0_2χ^0_2 and same-sign chargino production that could provide observable signals or Majorana tests, while sleptons remain highly suppressed due to cancellations. The work delivers a rigorous, gauge-consistent computational toolset for WBF SUSY predictions and clarifies parameter-space regions where WBF could inform MSSM measurements and fundamental properties of neutralinos and charginos at the LHC.

Abstract

We present a complete calculation of weak boson fusion production of colorless supersymmetric particles at the LHC, using the new matrix element generator SUSY-MadGraph. The cross sections are small, generally at the attobarn level, with a few notable exceptions which might provide additional supersymmetric parameter measurements. We discuss in detail how to consistently define supersymmetric weak couplings to preserve unitarity of weak gauge boson scattering amplitudes to fermions, and derive sum rules for weak supersymmetric couplings.

Figures (3)

• Figure 1: Cross sections with the inconsistent electroweak parameters relative to that with the consistent SLHA ripping scheme described in the text, as function of the hadronic center-of-mass energy. The red (solid) curve is for $\chi^+_1\chi^-_1$ pairs, the blue (dashed) curve for $\chi^+_1\chi^-_1$ production, and the green (dot-dashed) curve for The cuts of Eqs. (\ref{['eq:cut1']}) and (\ref{['eq:cut2']}) were imposed on the two jets.
• Figure 2: Cross section with varying Yukawa coupling relative to that with $\sigma_0(Y_f=m_f)$ for WBF $\tilde{\tau}^+_1\tilde{\tau}^-_1$ (red solid) and $\tilde{b}_1\tilde{b}^*_1$ (blue dashed) production. The cuts of Eqs. (\ref{['eq:cut1']}) and (\ref{['eq:cut2']}) are imposed on the two jets. The crosses represent the points where the Yukawa coupling is extracted from the masses and $A_f$, as described in the text.
• Figure 3: Representative Feynman diagrams for WBF neutralino pair production at a hadron collider: (a) $t$-channel chargino exchange; (b) $s$-channel $Z$ boson (or Higgs bosons, not shown); (c) $Z$ bremsstrahlung; (d) double--neutralino bremsstrahlung, which in most cases is a higher-order electroweak correction to on-shell squark-neutralino production.