Exclusive vector meson production at high energies and gluon saturation

Abstract

We systematically study exclusive diffractive (photo) production of vector mesons (J/ψ, ψ(2s), φ and ρ) off protons in high-energy collisions and investigate whether the production is a sensitive probe of gluon saturation. We confront saturation-based results for diffractive ψ(2s) and ρ production at HERA and J/ψ photoproduction with all available data including recent ones from HERA, ALICE and LHCb, finding good agreement. In particular, we show that the t-distribution of differential cross sections of photoproduction of vector mesons offers a unique opportunity to discriminate among saturation and non-saturation models. This is due to the emergence of a pronounced dip (or multiple dips) in the t-distribution of diffractive photoproduction of vector mesons at relatively large, but potentially accessible |t| that can be traced back to the unitarity features of colour dipole amplitude in the saturation regime. We show that in saturation models the dips in t-distribution recede towards lower |t| with decreasing mass of the vector meson, increasing energy or decreasing Bjorken-x, and decreasing virtuality Q. We provide various predictions for exclusive (photo) production of different vector mesons including the ratio of ψ(2s)/J/ψ at HERA, the LHC, and future colliders.

Spin effects in the pion holographic light-front wavefunction

“…(14) by the light-front energy denominator [28] yields the well-known photon light-front wavefunctions [28][29][30][31][32]. This assumption for the helicity structure of the vector meson is very common when computing diffractive vector meson production in the dipole model [31][32][33][34][35][36][37][38][39][40] and, as we mentioned earlier, was used in Ref. [19] with the holographic wavefunction for the ρ meson.…”

Low-x physics at LHeC/FCC-he and its implications on UHECR

“…Another sensitive test of the low x and saturation dynamics in this process, is provided by the measurement of the t dependence for different energies and for different vector mesons. It was observed in [6] that the t-profile of the elastic cross section has a characteristic dip in the presence of saturation. The position of the dip is dependent on the energy as well as on the mass of the vector meson and the virtuality of the photon if one considers DIS instead of the photo production.…”

Measurement of the cross-section ratio sigma(psi(2S))/sigma(J/psi(1S)) in deep inelastic exclusive ep scattering at HERA

“…Armesto and Rezaeian [39] (AR) calculate the cc-dipole cross section using the ImpactParameter-dependent Color Glass Condensate model (b-CGC) [40] as well as the Saturation (IP-Sat) [41] dipole model, recently updated with fits to the HERA combined data [42,43]. In the b-CGC model, which is restricted to the gluon sector, saturation is driven by the BFKL evolution, and its validity is therefore limited to x Bj …”