Ultra-forward particle production from CGC+Lund fragmentation

Abstract

We present an analysis of data on single inclusive pion production measured by the LHCf collaboration in high-energy proton-proton and proton-nucleus at ultra-forward rapidities, $8.8\le y\le 10.8$. We also analyse forward RHIC data for calibration purposes. Our analysis relies on the use of a Monte Carlo event generator that combines a perturbative description of the elementary scattering process at partonic level based on the hybrid formalism of the Color Glass Condensate with an implementation of hadronization in the framework of the Lund string fragmentation model. This procedure allows us to reach values of the momenta of the produced particles as low as detected experimentally $p_t\sim 0.1$ GeV. We achieve a good description of single inclusive spectra of charged particles and neutral pions at RHIC and the LHC respectively, and nuclear modification factors for proton-lead collisions at the LHC. Our results add evidence to the idea that particle production in the domain of very small Bjorken-$x$ is dominated by the saturation effects encoded in the unintegrated gluon distribution of the target. Being forward particle production of key importance in the development of air showers, we stress that this approach allows for a theoretically controlled extrapolation of our results to the scale of ultra-high energy cosmic rays, thus serving as starting point for future works on this topic.

13 pages, 7 figures

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• PYTHIA 6.4 Physics and Manual
• The Color Glass Condensate
• NLO evolution of color dipoles
• Quark contribution to the small-$x$ evolution of color dipole
• Triumvirate of Running Couplings in Small-x Evolution
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• Resumming double logarithms in the QCD evolution of color dipoles
• CGC predictions for p+Pb collisions at the LHC
• Single Inclusive Hadron Production at RHIC and the LHC from the Color Glass Condensate
• Forward Neutral Pion Production in p+p and d+Au Collisions at sqrt(s_NN)=200 GeV
• Direct numerical solution of the coordinate space Balitsky-Kovchegov equation at next to leading order
• Single-inclusive particle production in proton-nucleus collisions at next-to-leading order in the hybrid formalism
• Single inclusive forward hadron production at next-to-leading order
• Sensitivity of Extensive Air Showers to Features of Hadronic Interactions at Ultra-High Energies
• Forward Hadron Productions in high energy pp collisions from a Monte-Carlo generator for Color Glass Condensate

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• Saturation and forward jets in proton-lead collisions at the LHC
• Measurement of inclusive very forward jet cross sections in proton-lead collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV
• On the Threshold Resummation in Forward pA Collisions
• Complete Next-to-Leading Order Calculation of Single Inclusive ${\pi }^0$ Production in Forward Proton-Nucleus Collisions