Supervisors:  Dr. Brij Kishor Jashal (RAL/PPD) and Prof. Bill Murray (University of Warwick + RAL PPD)

ATLAS is one of four major experiments at CERN's Large Hadron Collider (LHC). Designed as a general-purpose detector, it is sensitive to a wide range of physical phenomena and focuses on searches for new physics as well as precision measurements of existing standard model processes. At the end of this decade ATLAS will install an ambitious set of upgrades to prepare for High-Luminosity LHC (HL-LHC), where nearly ten times the Run 1-3 LHC dataset will be recorded and greatly increase the experiment's sensitivity to new physics.

Multiple parton interactions (MPI) dominate the soft underlying event in proton–proton collisions at the LHC. Their modeling remains a major uncertainty in high-luminosity physics, as current Monte Carlo generators make different assumptions about the spatial diffusion of sea and valence quarks within the proton. While the “effective area" model describes double parton scattering (DPS), it lacks sensitivity to three-dimensional proton structure and centrality dependence.  This project aims to perform, for the first time in ATLAS, a study of triple parton scattering (TPS)  at Run 3 and HL-LHC conditions. In parallel, the project will explore a novel search for a light dilaton-like scalar (Φ), motivated by models predicting a first-order electroweak phase transition.

The technical focus of the PhD will be the development of dedicated High-Level Trigger (HLT) algorithms capable of selecting these rare, complex final states—both the multi-jet topologies relevant for triple parton scattering and the tt̄Φ final state relevant for the dilaton search—under HL-LHC pile-up conditions. The student will implement and test fast multi-object triggers, including online b-tagging and topological selections exploiting the upgraded Inner Tracker (ITk), ensuring efficient event capture within the 10 kHz HLT output rate.
This combined program connects deep-QCD structure studies with new physics searches.  The project contributes both to improved modeling of the underlying event and to expanding the discovery potential for scalar extensions of the Higgs sector at the HL-LHC. The student will therefore make a major contribution to ATLAS searches for new physics in an area that is one of the current hot topics for the field.

For more details, contact Dr. Brij Kishor Jashal (brij.jashal@stfc.ac.uk) or Prof. Bill Murray (bill.murray@stfc.ac.uk). ​