A search for a promising tetraquark candidate X(ud($)over-bar($)over-bar($)over-bar) in pn -> Lambda Lambda X

We propose to search for a tetraquark candidate X(ud ($) over bar($) over bar) in pn -> Lambda Lambda X(ud ($) over bar($) over bar) -> Lambda Lambda K(+)K(0) or Lambda Lambda KK*. The existence of a tetraquark state X(ud ($) over bar($) over bar) with J(P) = 0(+), 1(-) or 1(+) was predicted in the literature based on specific diquark effective degrees of freedom inside hadrons. In order to understand the underlying dynamics for exotic hadrons, a search for the tetraquark X(ud ($) over bar($) over bar) is strongly recommended. The proposed reaction involves two Lambda production, of which the narrow widths make it a great advantage in the analysis of the final-state missing mass spectrum. We make an estimate of the production rate of X(ud ($) over bar($) over bar) in an effective Lagrangian theory and find that for J(P) = 1(-) the sample events of similar to 2200nb(-1) will be able to identify X(ud ($) over bar($) over bar) with five standard deviations at a width of 10 MeV to K(+)K(0) near threshold. For J(P) = 1(+) with a width of 20 MeV to KK*, the sample events of similar to 130nb(-1) will be needed. Large production cross sections are expected in a kinematic region beyond the threshold. We emphasize the advantage of low background in this transition channel, and in the meantime caution the large uncertainties in the present estimate due to a lack of knowledge about the X(ud ($) over bar($) over bar) state. Implications for its heavy-flavored partners qq ($) over bar($) over bar and qq ($) over bar($) over bar are briefly discussed.