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

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 $ep/\ensuremath{\gamma}p$ 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 $2<{p}_{T}<\mathrm{\text{few}}\text{ }100\text{ }\text{ }\mathrm{GeV}$, 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.