Hide and seek: how PDFs can conceal New Physics

TL;DR

This paper investigates how uncertainties in proton structure, modeled by PDFs, can hide signs of new physics in LHC data, potentially biasing interpretations and highlighting the need for strategies to distinguish genuine signals from PDF effects.

Contribution

It introduces a systematic method to identify when global PDF fits might mask new physics signals and proposes strategies to disentangle these effects, emphasizing the importance of combined high-energy and low-energy measurements.

Findings

PDF fits can fully absorb signs of new physics in high-energy tails

Strategies to distinguish genuine signals from PDF-induced effects are proposed

Public analysis code enables testing robustness of BSM signals against PDFs

Abstract

The interpretation of LHC data, and the assessment of possible hints of new physics, require the precise knowledge of the proton structure in terms of parton distribution functions (PDFs). We present a systematic methodology designed to determine whether and how global PDF fits might inadvertently 'fit away' signs of new physics in the high-energy tails of the distributions. We showcase a scenario for the High-Luminosity LHC, in which the PDFs may completely absorb such signs of new physics, thus biasing theoretical predictions and interpretations. We discuss strategies to single out the effects in this scenario, and disentangle the inconsistencies that stem from them. Our study brings to light the synergy between the high luminosity programme at the LHC and future low-energy non-LHC measurements of large-$x$ sea quark distributions. The analysis code used in this work is made public so that any users can test the robustness of the signal associated to a given BSM model against absorption by the PDFs.