Electroweak Contributions to Squark Pair Production at the LHC

TL;DR

This work computes the complete leading-order electroweak contributions to squark-pair production at the LHC, including $s$-channel gauge-boson exchange and $t$/$u$-channel gaugino exchange, and analyzes their interference with dominant QCD amplitudes. The authors develop a master formalism with channel-specific functions ($\Phi,\chi,\Psi,\Upsilon,\Omega$) to obtain spin- and color-averaged squared amplitudes across all relevant parton subprocesses, for first- and second-generation squarks. Numerically, EW effects can modify the production rate of two SU(2) doublet squarks by about $10$–$20\%$ in typical mSUGRA/CMSSM scenarios, but in nonunified gaugino-mass models the corrections span roughly $-40\%$ to $+55\%$, with the total EW contribution to the full squark-pair cross section being about $1/3.5$ of the QCD term. The results highlight a strong dependence on gaugino masses and signs, and suggest EW contributions as a potential probe of the SUSY gaugino sector, especially through interference patterns and low-$p_T$ enhancements; however, precise experimental and theoretical control is required to exploit these effects in practice.

Abstract

In this paper we compute electroweak contributions to the production of squark pairs at hadron colliders. These include the exchange of electroweak gauge bosons in the s-channel as well as electroweak gaugino exchange in the t- and/or u-channel. In many cases these can interfere with the dominant QCD contributions. As a result, we find sizable contributions to the production of two SU(2) doublet squarks. At the LHC, they amount to 10 to 20% for typical mSUGRA (or CMSSM) scenarios, but in more general scenarios they can vary between -40 and +55%, depending on size and sign of the SU(2) gaugino mass. The electroweak contribution to the total squark pair production rate at the LHC is about 3.5 times smaller.

Figures (9)

• Figure 1: Feynman diagrams contributing to $u_i u_j \rightarrow \tilde{u}_{i\alpha} \tilde{u}_{j\beta}$. Here $i$ and $j$ are flavor indices, while $\alpha$ and $\beta$ label the 'chirality' of the squarks, with $1\ (2)$ standing for $L-$type ($R-$type) squarks. The index $m \in\{1,2,3,4\}$ labels the exchanged neutralino. The second, $u-$channel, diagram only exists for $i = j$.
• Figure 2: Feynman diagrams contributing to $u_i d_j \rightarrow \tilde{u}_{i\alpha} \tilde{d}_{j\beta}$. The notation in the $t-$channel diagram is as in Fig. \ref{['figF1']}. In the second, $u-$channel, diagram, which only exists of $i=j$, the chargino index $n$ runs from 1 to 2.
• Figure 3: Feynman diagram contributing to $u_i d_j \rightarrow \tilde{u}_{j\alpha} \tilde{d}_{i\beta}$ with $i \neq j$. The notation is as in the chargino exchange diagram of Fig. \ref{['figF2']}.
• Figure 4: Feynman diagrams contributing to $u_i \bar{u}_j\rightarrow \tilde{u}_{i\alpha} \bar{\tilde{u}}_{j\beta}$. The notation for the $t-$channel diagram is as in Fig.\ref{['figF1']}. The gauge boson exchanged in the second, $s-$channel, diagram, which only exists if $i=j$, can be a gluon, a photon or a $Z$ boson.
• Figure 5: Feynman diagrams contributing to $u_i \bar{u}_j\rightarrow \tilde{d}_{i\alpha} \bar{\tilde{d}}_{j\beta}$. The notation for the $t-$channel diagram is as in Fig.\ref{['figF3']}. The notation for the second, $s-$channel, diagram, which only exists if $i=j$, is as in Fig. \ref{['figF4']}.