Dr Holly Pacey

MultiHiggs Physics Currently focused on the first search for BSM effects which could enhance triple-Higgs production.

Searching for BSM using dataset topology. This project is an entirely new approach to LHC new-physics searches, exploiting for the first time the relationships between collider events, to discriminate between SM and beyond Standard Model (BSM) physics. A graph network is built in which individual events appear as nodes, with edges between events reflecting their similarity in kinematic space. Properties of the graph nodes describe the dataset topology, providing discrimination between BSM and SM processes based more on rarity and variability in the signal than a specific models kinematics. Considering several definitions of similarity provides a plethora of event variables that can be used in addition to existing kinematic information to achieve good sensitivity in a prototype electroweak supersymmetry search. Possible new physics searches benefitting from this approach, and the potential to attain model-independent sensitivity to new physics are currently being explored.
Part of a joint grant with Adelaide "Optimising the search for the next discovery in particle physics"

Searching for electroweak supersymmetry. This project was 2/3 of my PhD, where I was the main analyser in searches for electroweak supersymmetry (SUSY) in 2 lepton final states, primarily targetting chargino pair production decaying via W bosons, but also searching for direct slepton production and chargino production decaying via sleptons, placing world-leading limits at the time using the full ATLAS Run-2 dataset. I am also involved in future developments aiming to close the gap at low mass-splittings, having performed many initial studies on utilising machine learning (BDTs) for SUSY/SM classification, and using flavour symmetry to improve the data-driven standard model background estimate.

Detecting undetectable particles: missing transverse momentum (MET) I am the incoming MET Trigger Signature Co-ordinator, and I have been the co-leader of the 'missing transverse momentum and pileup jet tagging' group at ATLAS. We work on developing ATLAS's ability to infer the presence of otherwise undetectable particles, like neutrinos and dark matter, which is a crucial part of many searches and measurements at ATLAS. During my PhD I worked on calcuting uncertaintes on the missing transverse momentum reconstruction, which are used ATLAS-wide. Current work includes Machine learning approaches to improve MET reconstruction and define new MET-based variables to better discriminate between BSM and SM physics in searches, and devising new MET Calibration methods.

Data-driven searches for unexpected asymmetries The first paper in this theme searched for violation of lepton charge-flavour symmetries in emu events a unique data-data comparison with sensitivity to many BSM models, such as R-Parity violating supersymmetry (RPV-SUSY) and scalar leptoquarks.

"Global fits and future collider studies with GAMBIT I am a new member of the GAMBIT community. My latest research theme is to contribute to global fits of existing results in full BSM models, in order to establish which models of BSM parameter space are most favoured and should be targetted in future searches. I aim to interpret these also in the context of future collider sensitivity.