Speaker
Description
QCD instantons are non-perturbative, semiclassical solutions of the Yang–Mills equations that connect topologically distinct vacua and encode tunneling between them. They underlie key phenomena such as axial U(1)U(1)U(1) symmetry breaking, anomalous chirality violation via the axial anomaly, and contribute to the structure of the QCD vacuum and chiral symmetry breaking. Their observation would provide direct evidence of topological fluctuations and a unique window into non-perturbative dynamics beyond perturbation theory.
Searches for instanton-induced processes in proton–proton collisions at ATLAS, based mainly on inner detector data, remain inconclusive (yet) due to overwhelming QCD backgrounds and limited control of rare event topologies. This motivates the development of data-driven strategies and the exploration of complementary signatures.
We present recent progress using minimum-bias and ALFA-tagged datasets. Forward proton tagging with ALFA enhances sensitivity to diffractive topologies that may favor instanton-induced processes, improving the discrimination between signal-like and background events in ongoing ATLAS analyses.