Experimental Particle Physics Consolidated Grant 2015

Particle physics in general and particularly the quest to elucidate the nature of the recently discovered Higgs boson are in the mainstream of current public consciousness. With the CERN Large Hadron Collider (LHC) just about to restart with much extended energy reach to search for new phenomena, there has never been a more exciting time in the field. Birmingham has a balanced programme, exploiting both the full reach of the LHC in energy and precision, as well as other aspects of the unique capabilities of the CERN accelerator complex. We study the particle collisions and decays observed in these experiments with the aim of determining the ultimate structure of matter and the forces of nature. Our leadership positions within the ATLAS collaboration include that of the current Spokesperson. The ATLAS Experiment is designed to explore a wealth of particle physics topics at the highest energies ever reached in the laboratory. Of the billion collisions taking place per second, only a tiny fraction can be permanently recorded and analysed. Our group built, maintains and operates a major part of the highly sophisticated on-detector electronics (trigger system) which has the task of selecting the most interesting events and reducing the data rate by a factor of 1000 within two millionths of a second after collisions take place. We are also very active in analysing the resulting data, with a particularly strong team working on the detailed properties of the Higgs boson and the production and decays of the even more massive top quark. Other studies use LHC data to provide detailed probes of the nature of the strong force holding quarks together inside the proton. The LHC is expected to operate for a further two decades and to remain the paramount energy frontier facility in particle physics. An ambitious programme to upgrade both accelerator and detectors is underway to hugely increase the collision rate such that every year of operation after the upgrade will deliver the same amount of data as ten years before. This vastly increased amount of data gives unprecedented precision in measuring the properties of the Higgs boson (which only the LHC has the energy to produce) and in testing the theories of how mass arises in the Universe, while also allowing much greater sensitivity to physics beyond our current models. Birmingham is uniquely placed to contribute both to construction of a brand new, much more radiation-hard, tracking detector and to the upgraded trigger to handle the ten times larger data rate. Beyond ATLAS, our second major area of activity is in understanding the complex decays of heavy quarks. At the LHCb experiment, we are investigating the origins of the matter-antimatter asymmetry of the Universe by studying the tiny differences between the decay characteristics of bottom (b) quarks and their antiquarks. The huge rates of b quark production in LHCb (which is also being upgraded) give very high precision measurements and access to extremely rare decays, the area of particular interest in Birmingham. Our NA62 group studies the decays of strange particles to also search for new physics such as that suggested by supersymmetric models. The SPS accelerator complex has already restarted after the long shutdown, so NA62 are commissioning their detector and preparing for studies of the ultra rare process in which a kaon decays to produce a pion and two neutrinos. This process occurs only roughly once in every 10 billion kaon decays, but this tiny rate is particularly sensitive to new physics. Finally, the group contains key proponents of a number of possible future high energy projects, with particular emphasis on electron-positron and electron-proton colliders. We will continue in these leadership roles and be ready to step up our involvement should plans for these, or an even greater energy proton-proton collider, start to become closer to realisation.