Extensions of the Standard Model often predict light scalar or pseudoscalar states coupling preferentially to heavy fermions. In this seminar, we present two recent ATLAS searches for low-mass bosons decaying into bbˉ based on the full Run 2 dataset. The first search considers associated ZH production and probes exotic Higgs decays into four b-quarks via light scalars or pseudoscalars with the same or different mass (H→aa/a1a2→4b) or into six b-quarks via a longer decay chain (H→a1a2→3a1→6b). The second search targets instead associated production of ttˉ and tW with a pseudoscalar, exploring pseudoscalar masses down to ~12 GeV. In both searches, the boson is often produced with substantial Lorentz boost. This regime challenges standard b-tagging and jet reconstruction, and motivates the deployment of novel techniques such as large-radius jets with substructure, track-assisted taggers, and merging/unmerging strategies to identify bbˉ signatures. A dedicated secondary vertex reconstruction is also used to recover low-momentum b-hadrons. We will present the experimental strategies, algorithmic innovations, background estimation methods, and the obtained results, demonstrating how ATLAS is breaking new ground in searches for boosted, low-mass bbˉ resonances.
Refreshments will be served at 10h30