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-Du = 600 GeV, the low-energy constraint is vertical bar x(u)vertical bar <= 14:4, while the addition of the LHC dijet measurement leads to vertical bar x(u)vertical bar <= 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.