The Oxford Science Lecture Series

Dr   Pippa  Wells

CERN

"What has Particle Physics ever done for me?"

 Dorothy Hodgkin Memorial Lecture 2022

Somerville College, Oxford, 1st March 2022

Dr Pippa Wells is the Deputy Director of Research and Computing at CERN, the European laboratory for particle physics. After completing her doctorate at the University of Cambridge, she joined CERN to work on the OPAL experiment at the Large Electron-Positron collider. She subsequently moved to the ATLAS collaboration which is part of CERN’s flagship, the Large Hadron Collider, LHC. She was project leader of the ATLAS inner tracking detector, which measures charged particles as they emerge from the particle interaction point, and which played a crucial role in the discovery of the Higgs boson in 2012. She then coordinated studies to demonstrate the physics potential of a high-luminosity upgrade of the LHC, which will deliver ten times more collisions than the original design. From 2016 to 2020 she served as Head of Member State Relations, and she was appointed Deputy Director for Research and Computing in 2021.

Dr Wells started her talk by showing a map of CERN and Geneva, she indicated the track taken by the accelerator 100m underground, straddling the Swiss/French border. The project was started in 1954 and has grown over the years. Dr Wells explained that work at CERN covers four pillars: Research, Collaboration, Technology and Innovation, and Education and Training.

In their research, they look at what the universe is made of, the building blocks of matter and the forces that control their behaviour. Dr Wells explained that hitherto we have learnt about these by looking at the light from stars which takes us back in time. However, for the first 380,000 years after the Big Bang there was no light so we can’t learn about this early period of the universe’s existence in that way. At CERN they are trying to recreate the processes that were happening at that time by studying electrons, neutrinos and quarks. Dr Wells explained that with two types of quarks, up and down quarks, you can make protons and neutrons and then by adding in electrons and neutrinos you can look at everyday matter. She said that there are four other quarks (strange, charm, bottom and top) to consider, as well as the particles that arise from the forces between them (gluons, photons, W and Z bosons). She said that Margaret Thatcher visited CERN shortly before the W and Z bosons were identified and that she had asked to be informed about the discovery before anyone else! The Higgs boson arises from the force that gives particles mass. In 1964 (when Dorothy Hodgkin was awarded the Nobel prize), Peter Higgs, Robert Brout and François Englert predicted the existence of the particle. It was found in 2012 and the following year Higgs and Englert were awarded the Nobel Prize in physics.

To undertake research, CERN needs three different technologies, generators, detectors and computing/data storage. The LHC is 27 km in circumference and contains large superconducting magnets which steer particles through a vacuum in two beams, which are travelling in opposite directions at close to the speed of light. The particles are accelerated through three accelerators (the third of which is the one where the W and Z bosons were found) and emerge in a straight line into the LHC. There are four places around the ring where the particles are allowed to collide: Atlas, CMS, Alice (where particles collide with lead which contains 208 protons and neutrons) and LHCb (which looks at the difference between matter and antimatter) and there are more than 1 billion collisions per second! Neutrinos don’t interact with anything, they fly straight through the detector, but scientists can deduce that they were there when ‘something is missing’! In 2012, the ATLAS and CMS experiments announced they had each observed a new particle in the mass region around 125 GeV which was consistent with the theory proposed by Higgs, Brout and Englert.

Dr Wells showed photographs of the 7000 tonne Atlas experiment which is 25 metres high (see https://home.cern/science/experiments/atlas). There are layers and layers of electronics to capture the data. She explained that it is only possible to keep a portion of the data generated by the LHC so the science team have to decide which are important during the experiment. These are distributed and duplicated worldwide in 42 different countries. Three thousand scientists collaborated to design and build the experiment and around a thousand work on it at any time.

Dr Wells explained that, having identified the Higgs boson, they are now trying to explain what else is in the universe, scientists only really understand about 5% of it at the moment. They are exploring a range of questions including whether there are other particles like the Higgs boson, why haven’t matter and antimatter wiped each other out, how does gravity work? They are about to start the third run of the LHC which will continue for four years. Over the years, the collider has grown from 6 km to 27 km and now the plan is to extend it to 100 km. The next detector to be built should be developed to fully understand the Higgs boson.

When CERN was founded in 1954, twelve countries joined together to bring in scientists to build harmony and peace. CERN now has 23 members. There are associate members and observer states and the collaborating nations include several that are in conflict with each other, such as India and Pakistan, but where the scientists collaborate together without issue. There are 11-12,000 scientists who work at CERN (although not all once), 23% are women, over 3000 are PhD students and 750 are post-docs. The UK provides 875 collaborators, 670 of which are UK nationals. At the time of the lecture, Russia had just invaded Ukraine and Dr Wells explained that the CERN council was trying to decide how to implement the sanctions imposed on Russia but also support scientists from Russia who were speaking out against the actions of their country. CERN has been the model for similar collaborative facilities, such as SESAME in Jordan which is called ‘a light in the desert’.

Finally, Dr Wells discussed how technology developed at CERN has spread out into many, many areas. It was the birthplace of the World Wide Web. Dr Wells showed a draft of Tim Berners-Lee’s initial proposal which was marked as ‘vague but exciting’! Other developments have included improvements in x-ray technology, so that the technique can look at soft tissue, and Hadron therapy which uses a beam of protons or carbon ions to target a tumour more accurately with less damage to peripheral tissue. They are currently working to develop linear accelerators for use in low and middle income countries. There are about 150,000 visitors a year and they are now building a new outreach centre. CERN is part of the United Nations and has programmes on sustainability, energy and gender among many (see https://home.cern/about/what-we-do/train-educate-engage).

Dr Wells finished by taking a whole range of questions, which continued in the drinks reception that followed.

Prof. Carolyn Carr

Associate Professor of Biomedical Science

University of Oxford