A POWHEG generator for di-jet production in polarized proton-proton collisions

We present a new Monte-Carlo generator for the simulation of di-jet production in polarized proton-proton collisions at the next-to-leading order in QCD matched to parton showers using the framework of the POWHEG BOX. With this program we compute a variety of observables of immediate relevance for the spin program of the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. While parton-shower effects are generally small, we find that in some search regions their inclusion improves agreement of predictions with data. Moreover, we provide a critical assessment of selection criteria applied in experiment in the light of perturbative stability.

💡 Research Summary

The paper presents a novel Monte‑Carlo event generator for the simulation of di‑jet production in longitudinally polarized proton‑proton collisions, targeting the spin physics program at the Relativistic Heavy‑Ion Collider (RHIC). Building on the POWHEG BOX V2 framework, the authors extend the standard unpolarized implementation to include polarized parton distribution functions (PDFs) and the corresponding helicity‑dependent matrix elements at next‑to‑leading order (NLO) in QCD. The theoretical foundation is laid out by factorizing the polarized cross‑section into convolutions of polarized PDFs Δf(x,μ_F) and partonic cross‑sections Δĥσ, with explicit expressions for the longitudinally polarized combination of helicity configurations.

Implementation details focus on translating the NLO formula into the POWHEG formalism. The polarized Born term ΔB, virtual corrections ΔV, real‑emission contributions ΔR, and collinear counterterms ΔG are assembled from existing helicity amplitudes for 2→2 and 2→3 processes (Refs.