Searching for Exclusive W decays in ttbar events using the ATLAS detector at the Large Hadron Collider

Exclusive hadronic decays of the W-boson are predicted by the Standard Model but have never been observed. Depending on the decay mode, the expected branching fractions could be as high as 1 per million. This project aims to exploit the large sample of > 100 million top-quark-pair production events available from Run 2 of the LHC to search for such decays, as well as new similarly sized datasets from Run 3.

Each top quark decays to a bottom quark and W-boson. Exclusive W decay events can then be searched for by requiring that one W Boson decays to a charged lepton and neutrino and then studying the decay of the other W boson. The precise selection of which decay modes to study will be determined during the Ph.D, but initial candidate decays are: i) W+-> rho_0 + pi+/rho+, ii) W+-> D_s + gamma , iii) W-+> D0 pi+/rho+, iv) W+ -> D_s + J/Psi .

In addition to analysis of ttbar datasets, it is planned to study and develop dedicated triggers for exclusive decays in direct W production as part of this Ph.D. project. If successfully deployed these could potentially enhance the searchable sample of W bosons by two orders of magnitude compared to the top-quark pair production dataset.