Unravelling new physics signals at the HL-LHC with EIC and FPF constraints

Recent studies suggest that global fits of parton distribution functions (PDFs) might inadvertently “fit away” signs of new physics in the high-energy tails of the distributions measured at the high luminosity program of the LHC (HL-LHC). This could lead to spurious effects that might conceal key beyond the Standard Model (BSM) signatures and hinder the success of indirect searches for new physics. In this paper, we demonstrate that future deep-inelastic scattering (DIS) measurements at the Electron-Ion Collider (EIC), and at CERN via <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mi>FASER</a:mi><a:mrow><a:mi>ν</a:mi></a:mrow></a:mrow></a:math> and SND@LHC at LHC Run III, and the future neutrino experiments to be hosted at the proposed Forward Physics Facility (FPF) at the HL-LHC, provide complementary constraints on large-<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>x</c:mi></c:math> sea quarks. These constraints are crucial to mitigate the risk of missing key BSM signals, by enabling precise constraints on large-<e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>x</e:mi></e:math> PDFs through a “BSM-safe” integration of both high- and low-energy data, which is essential for a robust interpretation of the high-energy measurements.