The Underlying Event and the Total Cross Section from Tevatron to the LHC

TL;DR

This paper investigates the relationship between the total cross section, underlying event, and multiple partonic interactions in high-energy hadronic collisions, using models constrained by existing data and exploring implications for LHC measurements.

Contribution

It introduces a Monte Carlo eikonal model linking total cross section and underlying event, and derives constraints on model parameters for LHC energies.

Findings

Constraints on model parameters from current data

Predictions on how total cross section measurements at LHC could challenge existing models

Evidence suggesting the need for model extensions at higher energies

Abstract

Multiple partonic interactions are widely used to simulate the hadronic final state in high energy hadronic collisions, and successfully describe many features of the data. It is important to make maximum use of the available physical constraints on such models, particularly given the large extrapolation from current high energy data to LHC energies. In eikonal models, the rate of multiparton interactions is coupled to the energy dependence of the total cross section. Using a Monte Carlo implementation of such a model, we study the connection between the total cross section, the jet cross section, and the underlying event. By imposing internal consistency on the model, we derive constraints on its parameters at the LHC. By imposing internal consistency on the model and comparing to current data we constrain the allowed range of its parameters. We show that measurements of the total proton-proton cross-section at the LHC are likely to break this internal consistency, and thus to require an extension of the model. Likely such extensions are that hard scatters probe a denser matter distribution inside the proton in impact parameter space than soft scatters, a conclusion also supported by Tevatron data on double-parton scattering, and/or that the basic parameters of the model are energy dependent.