Investigating saturation effects and the virtual pion in leading neutron events at HERA with the dipole model

Abstract

We investigate events with very forward neutrons in $ep$ collisions at HERA using impact parameter dependent colour dipole models with and without saturation. This is the first study of the leading neutron process deploying these models. The model predictions are compared with the available HERA measurements for $6<Q^2<100$~GeV${}^2$, $70<W<245$~GeV. Our analysis shows that the models exhibit Feynman scaling, independent of $Q^2$. Our results demonstrate that the $W$ and $Q^2$ dependence of the cross section is independent of the presence of a forward neutron as predicted by the limiting fragmentation hypothesis, which is a consequence of Feynman scaling itself. We infer that the HERA leading neutron production inclusive data is insensitive to saturation physics and these cross sections may not be able to distinguish gluon saturation effects in future $ep$ colliders. We provide a good description of the leading neutron structure function $F_2^{LN}$ at small $x$ using an assumption that the small-$x$ structure of protons and pions is universal up to a normalisation. We also show that the observables in the exclusive diffractive measurements with a vector meson in the final state are more sensitive to saturation physics at small $x$ than inclusive measurements. At last, we provide a prediction for the $\hat{t}$ spectrum in exclusive vector meson production in the dipole model using Yukawa theory to model the virtual pion's spatial wave function.

arXiv comment22 pages, 9 figures

References in corpus (34)

• Saturation Effects in Deep Inelastic Scattering at low $Q^2$ and its Implications on Diffraction
• Saturation in Diffractive Deep Inelastic Scattering
• An Impact Parameter Dipole Saturation Model
• Exclusive diffractive processes at HERA within the dipole picture
• Improved Measurement of the $\bar{d}/\bar{u}$ Asymmetry in the Nucleon Sea
• Analysis of combined HERA data in the Impact-Parameter dependent Saturation model
• The Large Hadron-Electron Collider at the HL-LHC
• Measurement of gamma gamma* --> pi0 transition form factor at Belle
• Impact-parameter dependent Color Glass Condensate dipole model and new combined HERA data
• First Monte Carlo global QCD analysis of pion parton distributions
• Revealing proton shape fluctuations with incoherent diffraction at high energy
• Hadron tomography by generalized distribution amplitudes in pion-pair production process ${\gamma }^{\ast }\gamma \to {\pi }^0{\pi }^0$ and gravitational form factors for pion
• The proton charge radius
• QCD saturation at the LHC: comparisons of models to p+p and A+A data and predictions for p+Pb collisions
• Nuclear enhancement and suppression of diffractive structure functions at high energies
• On the Rise of the Proton Structure Function F_2 Towards Low x
• Leading neutron production in $e^{+}p$ collisions at HERA
• Measurement of Leading Neutron Production in Deep-Inelastic Scattering at HERA
• Saturation models of HERA DIS data and inclusive hadron distributions in p+p collisions at the LHC
• In depth analysis of the combined HERA data in the dipole models with and without saturation
• Study of ${\pi }^0$ pair production in single-tag two-photon collisions
• A unified description of diffractive deep inelastic scattering with saturation
• Gluon saturation and energy dependence of hadron multiplicity in pp and AA collisions at the LHC
• Leading neutron spectra
• Pion structure function from leading neutron electroproduction and SU(2) flavor asymmetry
• Investigating saturation effects in ultraperipheral collisions at the LHC with the color dipole model
• The color dipole BFKL-Regge expansion: from DIS on protons to pions to rise of hadronic cross sections
• Target Fragmentation in $pp$, $ep$ and $\gamma p$ Collisions at High Energies
• Electromagnetic charge radius of the pion at high precision
• Pion structure function at small x from DIS data
• Gluon saturation and Feynman scaling in leading neutron production
• Exclusive processes with a leading neutron in $ep$ collisions
• Leading neutron production at the EIC and LHeC: estimating the impact of the absorptive corrections
• Exclusive vector meson production with leading neutrons in a saturation model for the dipole amplitude in mixed space

Cited by in corpus (1)

• Geometric scaling in leading neutron events at HERA