# Can New Physics hide inside the proton?

## TL;DR

This paper develops a method to simultaneously determine proton structure and potential new physics effects using deep-inelastic scattering data, revealing how beyond Standard Model influences can be distinguished from standard parton distributions.

## Contribution

It introduces a novel approach to jointly fit PDFs and BSM effects within the NNPDF framework, enabling systematic disentanglement of new physics signals from proton structure.

## Key findings

- BSM effects can be reabsorbed into PDFs without proper analysis
- The method constrains SMEFT operators using deep-inelastic data
- Disentangling BSM effects improves the accuracy of proton structure understanding

## Abstract

Modern global analyses of the structure of the proton include collider measurements which probe energies well above the electroweak scale. While these provide powerful constraints on the parton distribution functions (PDFs), they are also sensitive to beyond the Standard Model (BSM) dynamics if these affect the fitted distributions. Here we present a first simultaneous determination of the PDFs and BSM effects from deep-inelastic structure function data by means of the NNPDF framework. We consider representative four-fermion operators from the SM Effective Field Theory (SMEFT), quantify to which extent their effects modify the fitted PDFs, and assess how the resulting bounds on the SMEFT degrees of freedom are modified. Our results demonstrate how BSM effects that might otherwise be reabsorbed into the PDFs can be systematically disentangled.