ATLAS is a large multi-purpose high energy physics experiment at the LHC, ATLAS is currently undertaking its third experimental run (2022-25) while simultaneously preparing to undergo a large ‘Phase-II’ upgrade in 2026-28, following which data taking is expected to recommence for the fourth experimental run in 2029 under the guise of the High-Luminosity LHC.

This jointly supervised ATLAS studentship will have both a technical focus from RAL towards preparations for Phase-II, and a physics focus from UCL towards the exploitation of the currently recorded dataset.    

The technical focus will be on ATLAS’ new multithreaded High Level Trigger (HLT) which discriminates physics interaction events in near real time using a large dedicated computing farm, keeping only a small fraction for further study by the collaboration. The student will work to improve and evolve the current system towards the Phase-II upgrade. Here, the network and computing farm architecture change significantly and the HLT’s input rate will rise from 100 kHz to 1 MHz. This work is likely to take the form of targeted improvements to the C++ and Python core framework software which steer the HLT execution, or towards the software which will enable track reconstruction from the new ATLAS Inner-Tracker system within the HLT.

The physics focus will be on precision electroweak measurements. The three-lepton final state is a powerful probe of several important physics processes. In the Standard Model, it can arise from WZ production and top-Z production, as well as continuum processes which do not involve an on-shell Z boson. A precise inclusive and model-independent measurement will extend knowledge of these processes both in precision and into the off-shell regions. It will also be a powerful input to Effective Field Theory fits searching for signs of physics beyond the Standard Model above the LHC energy scale, and will be directly sensitive to models which have mass states within reach. We will make such a measurement, unfolded to particle level, and use it to probe the Standard Model as well as physics beyond it. 

For more details, contact Tim Martin (tim.martin@cern.ch) or Jon Butterworth ​(j.butterworth@ucl.ac.uk).​