Recent searches for new light (pseudo)scalars decaying into a boosted bbˉ pair using the ATLAS detector

About

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

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