LHC Constraints on Scalar Diquarks

TL;DR

This paper combines LHC measurements with low-energy data to significantly tighten constraints on scalar diquarks, particles coupling to two quarks, especially for masses around 600 GeV.

Contribution

It introduces an integrated analysis of LHC and low-energy constraints on scalar diquarks, improving existing bounds and informing future predictions.

Findings

LHC data significantly improves diquark coupling constraints.

For 600 GeV diquarks, coupling bounds are tightened from ~14 to 0.15.

Additional measurements further refine the constraints.

Abstract

A number of years ago, low-energy constraints on scalar diquarks, particles that couple to two quarks, were examined. It was found that the two most weakly-constrained diquarks are $D^u$ and $D^d$, colour antitriplets that couple to $u_{R}^{i} u_{R}^{j}$ and $d_{R}^{i} d_{R}^{j}$, respectively. These diquarks have not been observed at the LHC. In this paper, we add the LHC measurements to the low-energy analysis, and find that the constraints are significantly improved. As an example, denoting $x^u$ as the $D^u$ coupling to the first and second generations, for $M_{D^u} = 600$ GeV, the low-energy constraint is $|x^u| \leq 14.4$, while the addition of the LHC dijet measurement leads to $|x^u| \leq 0.13$--$0.15$. Further improvements are obtained by adding the measurement of single top production with a $p_T$ cut. These new constraints must be taken into account in making predictions for other low-energy indirect effects of diquarks.