[Paper Review] Introduction to Forward Physics and Cosmic Rays at ISMD 2010

M. Grothe, F. Hautmann+1 more|arXiv (Cornell University)|Mar 30, 2011

Particle physics theoretical and experimental studies39 references6 citations

TL;DR

This paper introduces forward physics at the LHC, focusing on high-pT particle production in forward rapidities and its implications for cosmic ray physics. It presents theoretical frameworks—such as BFKL resummation and high-energy factorization—for describing multi-scale QCD processes, and demonstrates that forward jet correlations and parton shower effects (including finite-angle radiation and multiple parton interactions) significantly impact jet decorrelation and event generator tuning, with key results showing distinct differences in azimuthal decorrelation between models like Cascade and Pythia under varying energy and rapidity conditions.

ABSTRACT

We give a brief introduction to the topics discussed at the ISMD 2010 Symposium (Antwerp, 2010) on forward physics at the LHC and its interplay with cosmic rays physics.

Motivation & Objective

• To address the theoretical and experimental challenges in describing high-pT particle production in the forward region at the LHC.
• To investigate the role of multiple energy scales in forward hard processes, particularly the interplay between BFKL-type and collinear logarithmic corrections.
• To assess the impact of finite-angle gluon radiation and multiple parton interactions on jet decorrelation and event generator tuning.
• To connect LHC forward physics measurements with cosmic ray air shower modeling, using LHC data as a proxy for high-energy fixed-target collisions.
• To provide a framework for improving Monte Carlo event generators through forward-central jet correlation measurements.

Proposed method

• Utilizes high-energy factorization with simultaneous resummation of logarithms in rapidity (x) and transverse momentum (kT) to describe multi-scale QCD processes.
• Applies perturbative QCD resummation techniques, including BFKL and next-to-leading-logarithmic corrections, to model large-rapidity forward jet production.
• Compares predictions from parton-shower generators (Cascade, Pythia) with and without multiple parton interaction (MPI) effects to assess their impact on azimuthal decorrelation.
• Employs the Siscone jet algorithm (R = 0.4) to reconstruct forward and central jets and analyze their angular correlations.
• Analyzes particle and energy flow in inter-jet and away-from-jet regions to distinguish single-chain vs. multiple-chain radiation mechanisms.
• Examines Mueller-Navelet jet production and Higgs boson backgrounds in vector boson fusion channels to probe radiation effects across large rapidity intervals.

Experimental results

Research questions

• RQ1 How do finite-angle gluon radiation and multiple parton interactions affect the azimuthal decorrelation of forward and central jets?
• RQ2 To what extent do current Monte Carlo event generators accurately model forward jet production, and how can they be tuned using LHC data?
• RQ3 What is the relative contribution of single-chain vs. multiple-chain parton shower mechanisms in forward jet production, as revealed by energy flow observables?
• RQ4 How do BFKL-type and collinear logarithmic corrections interplay in high-energy forward physics, and what is the impact on theoretical predictions?
• RQ5 Can forward-backward jet correlations help disentangle QCD radiation effects from multiple parton interactions in Higgs boson searches via vector boson fusion?

Key findings

• The Cascade generator, which includes finite-angle radiation in single-chain showers, predicts a larger azimuthal decorrelation in forward-central jet pairs than Pythia, especially at high transverse energy (ET > 30 GeV).
• At low ET (ET > 10 GeV), the influence of multiple parton interactions is significant in Pythia, but diminishes at higher ET, where finite-angle effects dominate in Cascade.
• The shape of the Δφ distribution between forward and central jets is strongly affected by finite-angle corrections, even when the average Δφ remains relatively unchanged.
• Measurements of forward-central jet correlations provide a powerful tool for tuning Monte Carlo event generators, particularly for modeling jet activity in boosted Higgs and new physics searches.
• Energy flow observables in inter-jet and away-from-jet regions reveal that multiple parton interactions shift gluon radiation to higher x in initial-state chains due to reduced energy per chain.
• Forward-backward jet systems can probe Mueller-Navelet effects and help distinguish between competing QCD radiation mechanisms in Higgs boson backgrounds, especially under central jet veto conditions.