Birmingham Experimental Particle Physics Consolidated Grant 2022-25

Particle physics is a subject that captures the public imagination and can become headline news when major discoveries take place, such as that of the Higgs boson. With a large data set already collected at the CERN Large Hadron Collider (LHC) and the prospect of much more in the future, we are at a very exciting moment in the field. Birmingham has a balanced programme of running experiments, exploiting the full reach of the LHC in both 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. We have held senior leadership positions in the ATLAS experiment over the years. ATLAS 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 in the experiment per second, only a tiny fraction can be recorded permanently for analysis. 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. We are also very active in analysing the resulting data, with a strong team working on the detailed properties of the Higgs boson, the production and decays of the even more massive top quark and the subtle interactions between the carriers of the weak and electromagnetic forces (the W and Z bosons and the photon). Beyond ATLAS, the group is prominent in studying the decays of heavy quarks, which offer complementary sensitivity to new phenomena. The huge rates of beauty quark production in LHCb gives access to extremely rare decays, a Birmingham speciality being those of beauty baryons (combinations of three quarks similar to protons and neutrons). Our NA62 group studies particles containing strange quarks called kaons, including the ultra-rare kaon decay to a pion and two neutrinos, which happens only once in every 10 billion decays. Using the data taken so far, we have reported the most convincing observation of this decay so far, and will go on to study it further in future, exploiting its particular sensitivity to new physics. The LHC will remain the energy frontier facility in particle physics for a further two decades. An ambitious programme to upgrade both accelerator and detectors is underway. Every year after the upgrade (from 2027) will deliver the same number of collisions as ten years before, offering enormous new discovery potential, but also creating a very challenging experimental environment. For ATLAS, we are playing a major role in the construction of a much more radiation-hard and higher performance tracking detector and an upgraded trigger to handle the ten times larger data rate. Our LHCb and NA62 teams are also working on upgrades for future phases in the same era. The group has various fast-developing interests in non-collider areas of particle physics. These include the NEWS-G experiment, where we are developing novel spherical gas detectors to search for mysterious dark matter particles in a region of their mass that is not yet well explored. They also include preparations for DUNE, the largest-scale experiment ever to study the elusive neutrino particles; we are transferring our electronics expertise developed on ATLAS to contribute to DUNE data colection. We are active in preparations for next generation collider facilities, taking leadership roles in projects that plan to collide all combinations of electrons and protons and performing R&D into the detectors that will be required, including a growing interest in precision timing measurements. In another strand of our R&D, we are applying detectors developed in particle physics to new medical techniques such as hadron beam therapy.