Nuclear Theory·nucl-th

Wednesday·December 3, 2025

8 papers—6 primary·2 cross-listed

07
Non-diagonal DVCS with spinless hadron-to-two-hadron transition $γ^{*} π \to γ π π$
Sangyeong Son
We present the formalism of hadron-to-two-hadron transition generalized parton distributions (GPDs) for spinless hadron case. Definitions of the twist-2 unpolarized and polarized $π \to π π$ transition GPDs are introduced with a particular choice of kinematic variables that characterize the produced two-pion system. In the vicinity of $ρ (770)$ , we work out the two-pion decay angular distributions of the $e^{-} π \to e^{-} γ π π$ cross section, incorporating both the Bethe-Heitler and deeply virtual Compton scattering processes. Each cross section exhibits a distinctive angular distribution, which is sensitive to the polarization states of the produced $ρ (770)$ resonance. In addition, we construct the double partial-wave expansion of $π \to π π$ transition GPDs in the two-pion decay angles as a generalization of GPDs for transition from a pion to a spin- $ℓ$ resonance state. With the help of the Omnès representation, we constrain the $π \to π π$ transition GPDs in terms of the low energy $π π$ scattering phase shift and build a phenomenological model for these GPDs.
↳ hep-phnucl-thPoS(2026)·0 citations
08
Evidence of Spin-Interference Effects in Exclusive $J / ψ \to e^{+} e^{-}$ Photoproduction in Ultraperipheral Heavy-Ion Collisions
The STAR Collaboration
We report the first evidence of spin interference in exclusive $J / ψ \to e^{+} e^{-}$ photoproduction in ultraperipheral heavy-ion collisions at STAR at $s_{N N} = 200$ ~GeV. In Au+Au collisions, a negative $cos (2 ϕ)$ modulation is found for $p_{T} < 120$ ~MeV/ $c$ with a significance of $3.2 σ$ , while the isobar data (Ru+Ru, Zr+Zr) show a consistent negative modulation with a significance of $1.9 σ$ , opposite in sign to that in $ρ^{0} \to π^{+} π^{-}$ photoproduction. This establishes for the first time that the interference sign is controlled by the spin structure of the final-state daughters, resolving the ambiguity present in the all-boson $ρ^{0}$ channel. The compact $J / ψ$ probes gluon distributions at perturbative scales, resulting in a weaker modulation and providing stringent constraints on Color Glass Condensate calculations. These findings demonstrate that spin-dependent interference in heavy vector mesons provides a new, experimentally accessible handle on gluon structure beyond traditional cross-section measurements.
↳ nucl-exhep-exhep-phnucl-thPRL(2026)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Non-diagonal DVCS with spinless hadron-to-two-hadron transition γ∗π→γππ

Evidence of Spin-Interference Effects in Exclusive J/ψ→e+e− Photoproduction in Ultraperipheral Heavy-Ion Collisions

Affiliations

Non-diagonal DVCS with spinless hadron-to-two-hadron transition $γ^{*} π \to γ π π$

Evidence of Spin-Interference Effects in Exclusive $J / ψ \to e^{+} e^{-}$ Photoproduction in Ultraperipheral Heavy-Ion Collisions