Multiparton Interactions with an x-dependent Proton Size

TL;DR

This paper introduces a modified impact parameter model in Pythia 8 that accounts for the x-dependent size of the proton, improving the simulation of multiparton interactions by reflecting the narrower high-x parton distributions.

Contribution

It presents a novel x-dependent Gaussian profile for the proton in Pythia 8, enhancing the modeling of parton spatial distributions based on x value.

Findings

The x-dependent profile better matches theoretical expectations.

Improved modeling of high-x parton distributions.

Comparison shows advantages over default profiles.

Abstract

Theoretical arguments, supported by other indirect evidence, suggest that the wave function of high-x partons should be narrower than that of low-x ones. In this article, we present a modification to the variable impact parameter framework of Pythia 8 to model this effect. In particular, a Gaussian hadronic matter profile is introduced, with a width dependent on the x value of the constituent being probed. Results are compared against the default single- and double-Gaussian profiles, as well as an intermediate overlap function.