LHC constraints on scalar diquarks

Abstract

A bstract 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 $$ {u}_R^i{u}_R^j $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>u</mml:mi> <mml:mi>R</mml:mi> <mml:mi>i</mml:mi> </mml:msubsup> <mml:msubsup> <mml:mi>u</mml:mi> <mml:mi>R</mml:mi> <mml:mi>j</mml:mi> </mml:msubsup> </mml:math> and $$ {d}_R^i{d}_R^j $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>d</mml:mi> <mml:mi>R</mml:mi> <mml:mi>i</mml:mi> </mml:msubsup> <mml:msubsup> <mml:mi>d</mml:mi> <mml:mi>R</mml:mi> <mml:mi>j</mml:mi> </mml:msubsup> </mml:math> , 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 $$ {M}_{D^u} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>M</mml:mi> <mml:msup> <mml:mi>D</mml:mi> <mml:mi>u</mml:mi> </mml:msup> </mml:msub> </mml:math> = 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.