Transverse nucleon structure and diagnostics of hard parton-parton processes at LHC

TL;DR

This paper introduces a novel method to identify the transverse momentum threshold where particle production in high-energy proton-proton collisions is dominated by hard parton-parton interactions, using impact parameter distributions derived from exclusive scattering data.

Contribution

It proposes a new approach to determine the onset of hard scattering dominance in pp collisions through impact parameter and transverse multiplicity measurements, linking geometric correlations to parton dynamics.

Findings

Impact parameters in hard events are smaller than in minimum-bias collisions.

Average impact parameters are nearly independent of p_T in the 2 GeV to few 100 GeV range.

Transverse multiplicity as a function of p_T can identify the transition to hard process dominance.

Abstract

We propose a new method to determine at what transverse momenta particle production in high-energy pp collisions is governed by hard parton-parton processes. Using information on the transverse spatial distribution of partons obtained from hard exclusive processes in ep/gamma p scattering, we evaluate the impact parameter distribution of pp collisions with a hard parton-parton process as a function of p_T of the produced parton (jet). We find that the average pp impact parameters in such events depend very weakly on p_T in the range 2 < p_T < few 100 GeV, while they are much smaller than those in minimum-bias inelastic collisions. The impact parameters in turn govern the observable transverse multiplicity in such events (in the direction perpendicular to the trigger particle or jet). Measuring the transverse multiplicity as a function of p_T thus provides an effective tool for determining the minimum p_T for which a given trigger particle originates from a hard parton-parton process. Additional tests of the proposed geometric correlations are possible by measuring the dependence on the trigger rapidity. Various strategies for implementing this method are outlined.