Proposal for IPPP (UK National Phenomenology Institute), 2020-2023

Particle physics research informs us about the nature of matter on very small scales. As we step down the length scales below the length scale of the atom, 10^(-10) meters, and past the length scale of the atomic nucleus, 10^(-15) meters, we enter the realm of particle physics. In this realm there are three well identified interactions. First, the strong interactions, which are responsible for the binding of quarks and gluons to produce protons, neutrons and other particles collectively called hadrons. Second, the electroweak interactions, responsible both for the radiation of photons (light) from matter and the radiation of the carriers of the weak force, the W and Z bosons, discovered at CERN in the 1983. Third, the interactions of the Higgs bosons. The Higgs boson was discovered at CERN in 2012. The interactions of all of these ingredients are controlled by a mathematical structure, known as the Standard Model (SM) gauge theory of electromagnetic, weak and strong interactions. This theory has so far withstood all the challenges posed by various accelerators, of which the latest and most energetic is the LHC. The SM is confirmed - with the unification of electromagnetism and weak interactions proved and tested to one part per mille. Strong interaction effects have been tested to the percent level. The quarks, the ingredients of the hadrons, come in six different types which are referred to as flavours. Flavour phenomena have contributed as much as the gauge principle in shaping the overall structure of the SM and it is the existence of flavours that gives the SM its family and generation structure. In the quark sector the SM description of flavour phenomena and the CKM picture of mixing and CP violation is now verified at the few per cent level. In the lepton sector, the flavours of leptons are the electron, the muon and the tau and their associated neutrinos. The observation of neutrino oscillations, and the consequence that neutrinos have mass, calls for an extension of the SM. Detailed examination of the charged and neutral leptons is of increasing importance. Since 2015, the Large Hadron Collider (LHC) has been accelerating and colliding protons at much higher energies than ever before, close to the design energy of 14 TeV. This higher energy probes much shorter distance scales than ever before. The high energy reach of the LHC will also allow the detailed study of the Higgs boson and exploration of TeV scale physics. However, the LHC experiments are significantly more complex than any previous particle physics experiment. Identifying the nature of physics at the TeV scale will require intense collaborative efforts between experimentalists and theorists. On the theoretical side, high-precision calculations of SM processes are needed to distinguish possible signals of new physics from SM backgrounds. Possible hints of new physics need to be compared with different models of physics beyond the SM in order to disentangle the underlying structure of TeV-scale physics. The IPPP has already established close connections with the UK and international experimental groups and is perfectly placed to help maximise the UK contribution to understanding the LHC data. There is also a strong effort in planning and designing the next generation of particle physics experiments. The IPPP will continue its role in assessing the physics potential and the design of future accelerators. The next decade promises to be pivotal in our understanding of the microscopic world. The IPPP will address fundamental questions about electroweak symmetry breaking, the structure of space-time, flavour physics and CP violation, neutrinos and lepton-flavour violation, and how particle physics connects with astrophysics and cosmology.