We investigate double production in pp reactions near threshold using an effective Lagrangian approach, highlighting a significant OZI rule violation through hadronic processes. Our model includes t- and u-channel contributions from the nucleon and s-wave N^* resonances (N^* (1535, 1650, 1895) ), as well as the pentaquark-like state Pₛ (2071). In the s-channel, scalar (f₀), tensor (f₂), and pseudoscalar ( (2225) ) mesons are incorporated. The N, N^*, f₀, and f₂ contributions enhance the cross-section and generate peak structures near W=2. 2 GeV, consistent with JETSET data, while cusp structures arise from and threshold openings. Polarization observables, such as the spin density matrix element (SDME), further elucidate the underlying hadronic mechanisms.
Lee et al. (2025) studied this question.