Themes Publications


My research interests in particle physics concern experimentally testing the structure of spacetime symmetries and quantum theory. These principles underlie the Standard Model at the energy frontier and possible extensions, notably supersymmetry. I am actively involved in understanding how the ATLAS detector performs, data analysis and model interpretation, whose results have profound implications for the Higgs boson and dark matter.

Particle physics

What are the fundamental building blocks of the universe? How do they interact? The Standard Model and General Relativity are our current best theories of nature that sit on the core principles of spacetime symmetries and quantum theory. Yet, due to both theoretical arguments and observational inconsistencies, we know they cannot be the whole story. We need new data from experimental tests to extend our understanding of nature.


Why is gravity so weak compared to the other forces? Why is the Higgs boson so unexpectedly light? Supersymmetry is a speculative theory that could help answer these questions. It predicts new particles which could be discovered at the Large Hadron Collider at CERN, Switzerland. More technically, I think about how to interpret LHC searches and analyse data for colourless superparticles that decay into low energy final states.


The ATLAS Experiment is essentially a glorified camera, capturing images of proton-proton collisions at CERN with exquisite precision. Thousands of scientists work together to ensure the detector works seamlessly to analyse data at the energy frontier. These could glimpse signatures of new particles created at high energy collisions. On the operations side, I monitor the optical links in the silicon tracker subdetector.

Dark sectors

Arguably the most startling realisation of fundamental science in recent decades is that our universe is mostly dark. There is now overwhelming observational evidence for dark matter, from galaxy cluster collisions to the cosmic microwave background. It makes up over 80% of the matter in the universe, but does not emit, reflect nor absorb light. What particles is it made of? How can we exploit colliders to shine light on the possibility of a rich dark sector?


Find a full list of my publications at:

The soft lepton frontier for new physics

Analysing data collected by ATLAS to search for Higgsinos and compressed sleptons

ATLAS SUSY EWSummary higgsino

Search for electroweak production of supersymmetric states in scenarios with compressed mass spectra at sqrt(s)=13 TeV with the ATLAS detector

ATLAS Collaboration
December 2017, arXiv:1712.08119

I had the privilege of collaborating with an excellent international analysis team for this project. This work presents the first hadron collider sensitivity to some of the most challenging but sought-after scenarios of natural supersymmetry and dark matter involving so-called compressed mass spectra, namely Higgsinos and compressed sleptons. We probed these using the two leptons and missing transverse momentum final state, which were striking blind spots before Run 2 of the LHC. Soft lepton reconstruction down to 4 GeV — among the lowest used by the ATLAS Experiment — was crucial in opening world-leading sensitivity that surpasses nearly two-decade old LEP limits.


The LHC interpretation challenge

How do we interpret the results of searches pursued by LHC experiments?

Soft physics and interpretation challenge title slide

Analysing parameter space correlations of recent 13 TeV gluino and squark searches in the pMSSM

Alan Barr and Jesse Liu
Eur. Phys. J. C (2017) 77: 202.
Dark matter LHC and direct detection

LHC supersymmetry searches are designed around simplified models. These capture the key experimental kinematic (e.g. jet energies) and structural (e.g. number of electrons) features in a collision. But beyond this model-independent characterisation of signatures, they are toy models for interpretation. If our universe were supersymmetric, how do the sensitivity of these searches map onto realistic scenarios? This is the LHC interpretation challenge, and addressing this is the purpose of our paper.