LHC Constraints on Scalar Diquarks

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$^{u}$| ≤ 14.4, while the addition of the LHC dijet measurement leads to |x$^{u}$| ≤ 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.