The Purdue high energy physics group is involved in studies of particle physics, including the production and decay of Higgs bosons, top quarks, and electroweak bosons produced in proton-proton collisions.
Particle physics research attempts to answer fundamental questions about the nature of space itself, the matter that fills it and the physical laws that govern its behaviour and, consequently, the large-scale structure and behaviour of the Universe.
The study of fundamental particles – quarks, leptons, and the particles that mediate the forces between them – is carried out by experiments at high-energy particle accelerators, which probe the smallest distance scales observed in nature. Decades of research have led to a theoretical model of elementary particles and their interactions, called the ‘Standard Model’ (SM) of particle physics.
Accelerator-based research to solve particle physics mysteries
Detailed studies of these particles led to Purdue’s involvement in the construction and operation of major experiments at various particle accelerator facilities around the world. Purdue’s current accelerator-based research is conducted primarily using the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN).
The huge detectors at the LHC, such as the Compact Muon Solenoid (CMS), are operated by thousands of scientists organised in large collaborations. A team of Purdue University scientists play a key role in the data analysis and upgrade of the CMS detector in preparation for a tenfold increase in the sensitivity to the discovery of new particles. Inner parts of the CMS detector need to be prepared to endure radiation levels equivalent to the core of a nuclear reactor when the intensity of the proton beams in the LHC increases, aka the ‘High-luminosity phase of the LHC, HL-LHC’. Purdue has a critical role in these particle physics upgrade activities, which are funded by the US Department of Energy and the US National Science Foundation, which Fermilab and Cornell University lead.
Purdue is the centre of US activities for the design and manufacturing of a system of radiation-hard light-weight carbon-fibre composite structures able to support all CMS tracking and timing detectors, together weighing in at more than five metric tonnes. Not only will they face extreme levels of radiation, but the custom-designed large equipment also must be extremely lightweight, strong, and thermally conductive. The large structures of up to six metres are able to support 50 times their weight within tolerances of a few hundred micrometres to about one millimetre in order to meet the specifications.
The discovery of the Higgs boson in 2012 at the LHC marks the cornerstone of the Standard Model, solving complex issues in particle physics and explaining how elementary particles acquire mass. However, the Higgs mass of 125 GeV remains a mystery itself since the SM in current best understanding ‘predicts’ a huge shift of the Higgs boson mass to un-physically huge mass values at the Planck scale – called the hierarchy problem.
Top quarks are the heaviest elementary particles and are in a tight relationship with the Higgs boson and the hierarchy problem. However, the Higgs boson was discovered at 125 GeV, and hence, it is a yet-to-be-discovered unknown mechanism that must correct mass. We can test the SM at the precision level to discover new particles, which could solve this fundamental problem within particle physics. We strive for a deeper understanding of the interplay between top quarks and Higgs bosons by a variety of ‘probes’ or properties of the top quark: correlation of the spin of top quarks, top quark polarisation, or the existence of top quark partner objects, as well as the formation of hypothetical bound states of top quarks.
Entanglement: Accessing elusive phenomena in the realm of quantum mechanics
The entanglement of particles, specifically top quarks, translates to the quantum wave functions of originally two entangled particles possessing an inseparable component of the quantum wave functions even when they are moving far apart.
These non-local quantum phenomena offer an exciting window to particle physics phenomena controversially discussed over 100 years ago: the Einstein–Podolsky–Rosen (EPR) paradox. The Physics Nobel Prize of 2022 was awarded for this phenomenon of entangled states and its dramatic impact on technology, aka quantum computing and quantum information science.
The field of top quark particle physics is at a turning point, transitioning from analysing millions to, by the time of the HL-LHC, billions of top quarks. This vast number of top quarks allows us to scrutinise the SM at an unprecedented level and will even allow us to understand and shed light on another related and elusive quantum mechanical phenomenon: the violation of Bell’s inequality. With only around 10% of the expected data at the LHC recorded and only a subset being analysed right now, we are looking ahead at truly exciting times!
- Particle physics related to top quarks and their interplay with the Higgs boson to challenge the Standard Model to discover new physics;
- Fundamental tests of quantum mechanics: Entanglement & Bell’s inequality; and
- Instrumentation and Detector R&D for current and future colliders.