Gluon saturation and Feynman scaling in leading neutron production

Abstract

In this paper we extend the color dipole formalism to the study of leading neutron production in $e + p \rightarrow e + n + X$ collisions at high energies and estimate the related observables, which were measured at HERA and may be analysed in future electron-proton ($ep$) colliders. In particular, we calculate the Feynman $x_F$ distribution of leading neutrons, which is expressed in terms of the pion flux and the photon-pion total cross section. In the color dipole formalism, the photon-pion cross section is described in terms of the dipole-pion scattering amplitude, which contains information about the QCD dynamics at high energies and gluon saturation effects. We consider different models for the scattering amplitude, which have been used to describe the inclusive and diffractive $ep$ HERA data. Moreover, the model dependence of our predictions with the description of the pion flux is analysed in detail. We show that the recently released H1 leading neutron spectra can be reproduced using the color dipole formalism and that these spectra could help us to observe more clearly gluon saturation effects in future $ep$ colliders.Comment: 10 pages, 5 figure

Exclusive processes with a leading neutron inepcollisions

“…In Ref. [20] we proposed to relate N π with the dipole-proton scattering amplitude N p , usually probed in the typical inclusive and exclusive processes at HERA, assuming that…”

“…In view of the existing calculations of K, we would conclude that R q = 2/3 is probably too large. Since the effective value of this quantity is still an open question [16,17,23,24], we have considered in [20] that R q could be in the range 1/3 ≤ R q ≤ 2/3. With this basic assumption we have estimated the dependence of the predictions on the description of the QCD dynamics at high energies as well as the contribution of gluon saturation effects to leading neutron production.…”

“…[20], one source of uncertainty in the study of inclusive leading neutron production (in Fig. 1 on the left) is the fact that there are several processes which lead to the same final state.…”

“…In Ref. [20] we extended the color dipole formalism to leading neutron processes and demonstrated that the experimental data on the semi -inclusive reactions can be well described by this approach. Our goal in this paper is to further extend our previous analysis to exclusive processes and try to show that the color dipole formalism may also provide a unified description of leading neutron processes.…”

“…Using the same assumptions made in Ref. [20], we compare our predictions with the HERA data on ρ exclusive photoproduction and estimate the contribution of the absorption corrections to exclusive leading neutron processes. Taking into account these corrections we present predictions for the exclusive φ, J/Ψ and γ production associated with a leading neutron in ep collisions at the energies of HERA and future electron -proton colliders.…”