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  • Open Access

Off forward non-s-channel helicity conserving contributions to exclusive vector quarkonium production from the spin dependent BFKL Pomeron

Sanjin Benić1,* and Adrian Dumitru2,3,†

  • *Contact author: sanjinb@phy.hr
  • †Contact author: adrian.dumitru@baruch.cuny.edu
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Phys. Rev. D 112, 034025 – Published 25 August, 2025

DOI: https://doi.org/10.1103/7t3g-d4wr

Abstract

A novel contribution to off forward, exclusive vector quarkonium production, γ(*)+p→V+p, at high energy is derived which corresponds to a t-channel exchange of a Balitsky-Fadin-Kuraev-Lipatov (BFKL) hard Pomeron, with a helicity flip of the proton. This “spin-dependent BFKL Pomeron” is required in a consistent expansion in powers of the momentum transfer t≈−Δ⊥2 beyond first order. The spin-dependent Pomeron violates s-channel helicity conservation at O(Δ⊥2), and beyond. Expanding to leading twist only, it corresponds to generalized parton distributions Eg(x,t) for vanishing skewness. We derive explicit expressions for the eikonal BFKL amplitudes, to all orders in dipole size times momentum transfer, for all helicity configurations of the particles in the initial and final states. We also provide numerical estimates of the helicity flip two gluon exchange amplitude at moderate x from a light cone quark model of the proton. The spin dependent BFKL Pomeron could, in principle, be discovered via double spin asymmetries in e+p→e+p+J/ψ with a transversely polarized proton and longitudinally polarized electron in the initial state.

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Phys. Rev. D 112, 034025– Published 25 August, 2025
  • Received 13 June 2025
  • Accepted 28 July 2025
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