Research

Themes

My research focuses on creative tests of the Standard Model including the Higgs boson, searches for new particles such as dark matter, and laboratory probes of astroparticle physics. In ATLAS, I pioneer novel photon collider measurements, develop synergies with cosmic-ray science, and construct the next-generation silicon tracker in the Cambridge cleanroom. Recently, I proposed the BREAD experiment to reveal axion dark matter using emerging quantum technologies.

SUSY Dark Matter

Supersymmetry and dark matter

A startling realisation of physics is that 80% of the matter in our Universe is missing. This is dark matter and supersymmetry predicts it could be created and discovered at the Large Hadron Collider. My PhD research identified promising scenarios of supersymmetric dark matter involving partners of the Higgs boson (Higgsino) and charged leptons (sleptons). I then led new ATLAS searches resulting in world-leading sensitivity, and created the canonical Higgsino and slepton summary plots widely shown at international conferences.

Silicon detectors

ATLAS and silicon detectors

Particle detectors are our eyes to the microcosm. In Autumn 2021, I joined the Inner Tracker (ITk) Phase II Upgrade project. I proved production readiness of the Cambridge cleanroom, leading assembly and quality control of the next-generation silicon tracker. I also led performance studies for the ATLAS Forward Proton (AFP) silicon pixels critical to its first physics results. In my PhD, I studied radiation damage of the ATLAS silicon tracker (SCT) and real-time algorithms to select dark matter signatures (L1 Topo trigger).

Photon collision

Colliding light at the LHC

Photons surrounding LHC protons and ions can collide to create new particles. I led the first publication using the AFP spectrometer to measure proton scattering when light collides into leptons. I also invented the strategy to measure the tau magnetic moment using heavy-ion collisions, which ATLAS and CMS recently pioneered in landmark results. I now convene the ATLAS Standard Model Soft QCD group, coordinating international efforts to uncover enigmatic non-perturbative dynamics, forward physics, and cosmic rays.

Axion dark photon

Axions and dark photons

Sub-eV mass dark matter such as axions can modify Maxwell's equations and create photons we detect in the lab. Detecting the low predicted signal rates requires pushing quantum sensing technology into uncharted territory. With US collaborators, I proposed a new experiment called BREAD to directly detect milli-eV mass dark photons and axions with broadband discovery sensitivity. For this project, I constructed a Fourier transform spectrometer at Chicago to test terahertz and infrared optics.

Higgs self-coupling

The origin of mass

The Higgs boson discovery opens novel experimental probes of electroweak symmetry breaking and new interactions. I led Higgs pair simulations to project Higgs self-interaction measurements using decays into four bottom quarks at the HL-LHC upgrade. This study deploys modern machine learning methods to improve signal sensitivity. This cornerstone program at the HL-LHC aims to reveal how particles acquired mass in the early Universe.

Tau pairs Feynman diagram

Theoretical physics

Particle phenomenology bridges theoretical models with experimental signatures. I performed large-scale simulations to interpret the broad LHC search program. I proposed new measurements and searches in key theory papers that opened a groundbreaking photon collider program. For my master's research, I developed the field theory of continuous-spin particles. As an undergraduate, I studied jet pileup mitigation for LHC upgrades.

Multi-muon cosmic ray event

Cosmic ray science

Cosmic rays are the highest energy particles we see on Earth but their origins remain enigmatic. Above peta-electron-volts, their measurement requires air showers, which ATLAS can observe as striking multi-muon bundles. Their interpretation requires hadronic models underpinned by LHC forward physics measurements I coordinate as Soft QCD convenor. Recently, I proposed creative astroparticle physics initiatives using ATLAS cosmic-ray data.

Papers

Phenomenology

Broadband Solenoidal Haloscope for Terahertz Axion Detection
Jesse Liu, Kristin Dona, Gabe Hoshino, Stefan Knirck, Noah Kurinsky, Matthew Malaker, David W. Miller, Andrew Sonnenschein, Mohamed H. Awida, Peter S. Barry, Karl K. Berggren, Daniel Bowring, Gianpaolo Carosi, Clarence Chang, Aaron Chou, Rakshya Khatiwada, Samantha Lewis, Juliang Li, Sae Woo Nam, Omid Noroozian and Tony X. Zhou
Phys. Rev. Lett. 128 (2022) 131801, arXiv:2111.12103
On The Cover and PRL Editors' Suggestion
UChicago News Release

Higgs self-coupling measurements using deep learning in the bb̅bb̅ final state
Jacob Amacker, William Balunas, Lydia Beresford, Daniela Bortoletto, James Frost, Cigdem Issever, Jesse Liu, James McKee, Alessandro Micheli, Santiago Paredes Saenz, Michael Spannowsky and Beojan Stanislaus
JHEP 12 (2020) 115, arXiv:2004.04240

New physics and tau g−2 using LHC heavy ion collisions
Lydia Beresford and Jesse Liu
Phys. Rev. D 102 (2020) 113008, arXiv:1908.05180
ParticleBites feature

Search Strategy for Sleptons and Dark Matter using the LHC as a Photon Collider
Lydia Beresford and Jesse Liu
Phys. Rev. Lett. 123 (2019) 141801, arXiv:1811.06465

Analysing parameter space correlations of recent 13 TeV gluino and squark searches in the pMSSM
Alan Barr and Jesse Liu
Eur. Phys. J. C 77 (2017) 202, arXiv:1608.05379

First interpretation of 13 TeV supersymmetry searches in the pMSSM
Alan Barr and Jesse Liu
arXiv:1605.09502
Oxford physics highlight

Analysis

Observation of the 𝜸𝜸 → 𝝉𝝉 process in Pb+Pb collisions and constraints on the 𝝉-lepton anomalous magnetic moment with the ATLAS detector
ATLAS Collaboration (JL Editor)
In Press Phys. Rev. Lett. (2023), arXiv:2204.13478, STDM-2019-19
PRL Editors' Suggestion, ATLAS Physics Briefing

Observation and Measurement of Forward Proton Scattering in Association with Lepton Pairs Produced via the Photon Fusion Mechanism at ATLAS
ATLAS Collaboration (JL Editor and Lead Analyzer)
Phys. Rev. Lett. 125 (2020) 261801, arXiv:2009.14537, STDM-2018-16
ATLAS Physics Briefing, ATLAS ICHEP highlights
CERN Courier feature, Press Release

Search for electroweak production of supersymmetric states in scenarios with compressed mass spectra at √s = 13 TeV with the ATLAS detector
ATLAS Collaboration (JL Editor and Lead Analyzer)
Phys. Rev. D 97 (2018) 052010, arXiv:1712.08119, SUSY-2016-25
ATLAS Physics Briefing on Higgsinos, Briefing on sleptons
CERN Courier feature, Oxford physics highlight

Instrumentation

Design and performance of a multi-terahertz Fourier transform spectrometer for axion dark matter experiments
Kristin Dona, Jesse Liu, Noah Kurinsky, David Miller, Pete Barry, Clarence Chang and Andrew Sonnenschein
JINST 17 (2022) P06014, arXiv:2104.07157

In situ radiation damage studies of optoelectronics in the ATLAS SemiConductor Tracker
Ian Dawson, Bruce Gallop, Jesse Liu, Peter Miyagawa, Peter Phillips, Gavin Pownall, Dave Robinson and Anthony Weidberg
JINST 14 (2019) P07014
Preliminary results: SCT-2018-003, SCT-2017-003, SCT-2016-002

Thesis

Discovery strategies for dark matter and Higgsinos at the LHC
Jesse Liu
CERN-THESIS-2019-088, Oxford Research Archive

I am author on all papers signed 'ATLAS Collaboration' since 2017.
Listed here are public references with leading or major personal contributions.
Particle physics convention lists authors alphabetically.

Find a full list of my papers at inspire:

all small author list

Talks

LHC Reinterpretation Workshop, CERN — Reinterpretation Workshop, CERN

Invited Seminars

Sorbonne Université, France, LPTHE Jussieu Seminar, 3 Oct 2023
Institut d'Astrophysique de Paris, France, ICAP Seminar, 22 Jun 2023
University of Sydney, Australia, CPPC Seminar, 4 May 2023
Johns Hopkins University, USA, Experimental Particle Physics Seminar, 5 Apr 2023
Massachusetts Institute of Technology, USA, LNS Colloquium, 27 Feb 2023
Brown University, USA, High Energy Experiment Seminar, 15 Feb 2023
University of Edinburgh, UK, Experimental Particle Physics Seminar, 27 Jan 2023
University of Bristol, UK, Particle Physics Seminar, 7 Dec 2022
University of Liverpool, UK, HEP Seminar, 16 Nov 2022
Imperial College London, UK, HEP Seminar, 15 June 2022
University of Warwick, UK, Particle Physics Seminar, 9 June 2022
Cornell University, USA, LEPP Journal Club Seminar, 6 May 2022
Perimeter Institute for Theoretical Physics, Canada, Particle Physics Seminar, 3 May 2022
'Colliding light, tau g-2, and broadband axion detection'

Case Western Reserve University, USA, Particle/Astrophysics Seminar, 1 March 2022
University of Cambridge, UK, Cavendish HEP Seminar, 30 Nov 2021
'Colliders and cosmic origin stories'

University of Tennessee, Knoxville, USA, HEP Seminar, 8 Sep 2021
Cornell University, USA, LEPP Journal Club Seminar, 30 Oct 2020
Stony Brook University, USA, Particle Physics Seminar, 19 Oct 2020
University of Pittsburgh, USA, PITT PACC Seminar, 5 Aug 2020
SLAC, Stanford University, USA, Elementary Particle Physics Theory Seminar, 12 Feb 2020
Fermilab, USA, Cosmic Physics Center Chalk Talk, 14 Nov 2019
Fermilab, USA, LHC Physics Center Physics Forum, 31 Oct 2019
'Colliding light to make dark matter and measure tau g–2'

University of Cambridge, UK, Cavendish HEP Seminar, 19 Feb 2019
LBNL, University of California, Berkeley, USA, Research Progress Meeting Seminar, 20 Nov 2018
'New frontiers in LHC discovery strategies'

SLAC, Stanford University, USA , Joint Theory–Experiment Seminar, 20 Apr 2018
Perimeter Institute for Theoretical Physics, Canada, BSM Seminar, 17 Apr 2018
University of California, Santa Cruz, USA, SCIPP Seminar, 10 Apr 2018
'Supersymmetry: closing the gaps at the LHC'

University of Oxford, UK, Dalitz Seminar in Fundamental Physics, 19 Jan 2017
University of Cambridge, UK, Joint DAMTP–Cavendish Seminar, 13 Jan 2017
'Soft physics and interpretation challenges for LHC supersymmetry searches'

Conference & Workshop Presentations

BREAD Collaboration Meeting, Chicago, USA, 5 Oct 2023
'Primer: Sensitivity of Dish Antennas - Why we need more'

EPS HEP 2023, Hamburg, Germany, 24 Aug 2023
'BREAD: Broadband Reflector Experiment for Axion Detection'

Dark Matter beyond the Weak Scale, Liverpool, UK, 28 Mar 2023
'Terahertz axion detection with BREAD'

Photon-induced Processes, Durham, UK, 3 Nov 2022
'Forward physics and colliding light at the HL-LHC'

Dark Matter UK, London, UK, 22 Sep 2022
ICHEP 2022, Bologna, Italy, 8 Jul 2022
'BREAD: Broadband Reflector Experiment for Axion Detection'

IoP Joint APP HEPP Conference 2022, Harwell, UK, 5 Apr 2022
'Colliding light, tau g-2, and axion detectors'

Snowmass CF2 Wavelike Dark Matter Meeting, Online, 8 Oct 2021
'BREAD: Broadband Reflector Experiment for Axion Detection'

APS DPF Meeting, Florida State, Online, 14 Jul 2021
'Colliding light: photon fusion production at ATLAS'

Phenomenology Symposium, Pittsburgh, Online, 25 May 2021
'New spin 0 physics from TeV to THz'

APS April Meeting, Online, 20 Apr 2021
'Turning Light Into Matter: First Physics Results Using ATLAS Forward Proton'

DIS 2021, Stony Brook, USA, Online, 14 Apr 2021
'Measurements of diffractive physics and soft QCD at ATLAS'

LHC Forward Physics Meeting, CERN, Online, 4 Mar 2021
'Exclusive dilepton production in ATLAS'

Workshop on Forward Physics and QCD with LHC, EIC and Cosmic Rays, Jefferson Lab, Online, 23 Jan 2021
'ATLAS Forward Proton'

Snowmass EF09 meeting, Online, 4 Sep 2020
'Colliding light to search for BSM phenomena'

ICHEP 2020, Online, 31 Jul 2020
'Colliding light to make dark matter at the LHC'
ICHEP 2020, Online, 30 Jul 2020
'The Alignment of the ATLAS Forward Proton Detector'

Snowmass Energy Frontier "Open questions and new ideas", Online, 8 Jul 2020
'Dark matter and tau g-2 using the LHC as a photon collider'

Higgs Couplings 2019, Oxford, UK, 2 Oct 2019
'Colliding light to measure tau g–2'

Young Experimentalists and Theorists Institute, Durham, UK, 8 Jan 2019
LHC Forward Physics Workshop, CERN, Switzerland, 18 Dec 2018
'Photon collider opportunities for new physics: SUSY and dark matter'

SUSY 2018, Barcelona, Spain, 23 Jul 2018
'Reconstruction techniques in ATLAS SUSY searches'

ICHEP 2018, Seoul, South Korea, 6 Jul 2018
ICHEP Prize Talk, 11 Jul 2018
'Innovative strategies in compressed electroweak SUSY searches'

DM@LHC 2018, Heidelberg, Germany, 5 Apr 2018
Institute of Physics Conference 2018, Bristol, UK, 27 Mar 2018
Young Theorists Forum 2018, Durham, UK, 10 Jan 2018
'Opening the soft lepton frontier for new physics at the LHC'

Young Theorists Forum 2017, Durham, UK, 11 Jan 2017
2nd LHC BSM Reinterpretation Workshop, CERN, Switzerland, 14 Dec 2016
'Parameter space correlations of 13 TeV SUSY searches'

BUSSTEPP 2016, Manchester, UK, 31 Aug 2016
1st LHC BSM Reinterpretation Workshop, CERN, Switzerland, 17 Jun 2016
'Phenomenological interpretations of strong SUSY searches'

Collaboration Plenaries

ATLAS ITk Strips Module Meeting, Online, 18 Jul 2023
'Module thermocycling: cold high-voltage breakdown observations'

ATLAS Standard Model Workshop, Prague, Czechia, 12 Sep 2023
ATLAS UK Meeting, Manchester, UK, 9 Jan 2023
'Cosmic ray science in ATLAS'

ATLAS SUSY Workshop, CERN, Switzerland, 19 Sep 2022
'Photon fusion'

ATLAS ITk WP12 Meeting, Birmingham, 31 Mar 2022
'Towards production: procedures and reporting'

ATLAS Upgrade Physics, Online, 22 Apr 2021
'AFP at HL-LHC'

ATLAS SM Group Plenary, Online, 15 Apr 2021
'Cosmic ray physics at ATLAS'

ATLAS Run 4 Roman Pot Meeting, Online, 26 Mar 2021
'AFP at HL-LHC: Physics and experimental overview'

ATLAS Idea Day, Online, 20 Jan 2021
'Cosmic ray physics at ATLAS'

ATLAS Roman Pot General Meeting, Online, 7 Oct 2020
'Lessons learned from dilepton AFP analysis'

ATLAS SM Jamboree, Online, 30 Sep 2020
'Summary of ATLAS Roman Pot exploitation opportunities'

ATLAS SM Group Plenary, Online, 2 Jul 2020
'Exclusive dilepton production with AFP'

ATLAS Week Plenary, Online, 24 Jun 2020
'Photon fusion production with and without ATLAS Forward Proton'

ATLAS Roman Pot General Meeting, CERN, Switzerland, 23 Jan 2020
'Exclusive dilepton production with proton tag'

ATLAS UK Exotics SUSY Meeting, Cambridge, UK, 11 Apr 2019
'Photon collider SUSY/DM searches with forward proton detectors'

ATLAS SUSY Group Plenary, CERN, Switzerland, 19 Jul 2018
'Physics highlights at recent international conferences'

ATLAS Exotics Workshop, Rome, Italy, 29 May 2018
'Opening the monojet + soft lepton frontier for dark matter' (poster)

ATLAS Week Plenary, CERN, Switzerland, 21 Feb 2018
'Latest SUSY results'

ATLAS Analysis Open Presentation, CERN, Switzerland, 1 Nov 2017
'Search for Higgsinos and compressed sleptons'

ATLAS Joint Exotics-SUSY Workshop, Bucharest, Romania, 12 May 2017
'Phenomenological studies of ATLAS SUSY searches'

ATLAS UK Meeting, University of Liverpool, UK, 5 Jan 2017
'New innovative ideas and analyses in supersymmetry'

ATLAS Week Plenary, CERN, Switzerland, 17 Oct 2016
'Semiconductor tracker: status report'

Instrumentation

Silicon detectors, ATLAS Inner Tracker (ITk) strips upgrade, tabletop spectrometer

For the ATLAS ITk upgrade, I lead silicon strips module assembly and quality control, qualifying the Cambridge cleanroom for a production goal of over 1000 modules. I have wide-ranging laboratory expertise in module assembly, metrology, wire bonding, electrical testing, and thermal cycling quality control. At Chicago, I designed and constructed a tabletop terahertz-infrared spectrometer, managing operations and data acquisition, to characterize calibration optics for axion detector R&D.

Wirebond testing — Hybrid preparation / Photo: B. Hommels

Photon collider science

Energy frontier tests of QED, turning light into (dark) matter

Observation and measurement of forward proton scattering in association with lepton pairs produced via the photon fusion mechanism at ATLAS

ATLAS Collaboration

arXiv:2009.14537, Phys. Rev. Lett. 125 (2020) 261801

I co-led a small team to produce this landmark result announced at ICHEP 2020. It is the first physics analysis using the ATLAS Forward Proton (AFP) spectrometer, a new class of LHC instrument installed in 2017 at ATLAS. For me, this result is exciting because not only is it a new analysis, it's also not every day in ATLAS you get a new kind of detector to understand and play with. It's a real treat for experimentalists! The physics itself is sublime: we're seeing light turning into matter and antimatter. This result observes the scattered intact protons when light turns into dielectron or dimuons. We also understand the detector reconstruction to a level that allows us to perform the first cross-section measurements using AFP. With so many novelties in one analysis, this opens up an exciting new programme at the LHC to use proton-tagging for measurements and searches.

New physics and tau g−2 using LHC heavy ion collisions

Lydia Beresford and Jesse Liu

arXiv:1908.05180, Phys. Rev. D 102 (2020) 113008

The muon g–2 has a longstanding 3.7 sigma tension with prediction and new physics interpretations such as supersymmetry have been widely studied. With a larger mass, the tau g–2 can be much more sensitive to new physics but is rarely discussed. The strongest constraints come from LEP, which is an order of magnitude away from the central value and even the sign remains elusive. Interestingly, photon collisions using heavy ions could open new advances, given the exceptionally clean environment and huge photon flux. The key to our proposal is introducing the strategy amenable for ATLAS or CMS to implement using data already collected at the LHC.

Photon collider search strategy for sleptons and dark matter at the LHC

Lydia Beresford and Jesse Liu

arXiv:1811.06465, Phys. Rev. Lett. 123 (2019) 141801

Slepton sensitivity with photon collider

When LHC beams cross, photons from the proton electromagnetic fields can collide to make new particles. The protons remain intact, travel down the beampipe, and are detected by very forward detectors. This allows us to reconstruct initital state information and the full missing momentum 4-vector — impossible in usual head-on collisions. My collaborator and I exploit these unique features to propose a search strategy that uncovers the blind spot where the slepton is 15 to 60 GeV heavier than the dark matter. Remarkably, this is the region favoured by non-collider data from cosmology and muon magnetic moment measurements.

Supersymmetry and dark matter

Higgsinos, compressed sleptons, beyond simplified models

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

ATLAS Collaboration

arXiv:1712.08119, Phys. Rev. D 97 (2018) 052010

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. I led important validation studies during the transition to new reconstruction and simulation software for the improved analysis that uses 4 times as much data collected in the full LHC Run 2 [arXiv:1911.12606]. I also produced the first Higgsino dark matter and slepton-bino SUSY summary plots [ATL-PHYS-PUB-2019-022], which are regularly presented at conferences.

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

Alan Barr and Jesse Liu

arXiv:1608.05379, Eur. Phys. J. C (2017) 77: 202

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.

First interpretation of 13 TeV supersymmetry searches in the pMSSM

Alan Barr and Jesse Liu

arXiv:1605.09502

This is the first interpretation of six early 13 TeV ATLAS searches for supersymmetry within the 19-parameter 'phenomenological MSSM' theoretical framework. This work was referenced by several speakers at major summer conferences, and used by the SUSY-AI Online effort.