NWO Physics 2026, Conference

Abstract

Since the discovery of the Higgs boson in 2012, no new particle has been observed directly, suggesting that potential new physics may lie at energy scales well beyond the electroweak one. This motivates the use of Effective Field Theories, such as the Standard Model EFT (SMEFT), to search for new physics indirectly at hadron colliders. Such searches require high precision, and one of the main bottlenecks is the determination of the Parton Distribution Functions (PDFs), describing the proton structure.

In this talk, I discuss the delicate balance between using high-energy observables to better constrain PDFs in the large Bjorken-x region, which is the most relevant for new physics searches, and the risk of inadvertently fitting away new physics signals into the PDF parametrisation itself. I explore two complementary strategies for robust searches: (i) fitting the PDFs and SMEFT parameters simultaneously, and (ii) fitting them separately with a “conservative” determination of the PDFs, using only observables that can safely be considered SM-like.

I compare both methodologies in controlled closure tests using Drell-Yan and top pseudodata. Finally, I conclude by proposing best-practice recommendations for robust SMEFT searches at colliders.