Scientists working at the Large Hadron Collider in Geneva may finally have tracked down the elusive Higgs boson. Results announced today at CERN show that a new heavy particle has been identified, with all the properties expected of the Higgs. Bristol physicists working at the CMS experiment played a key role in establishing this exciting new result which is the culmination of twenty years’ work.
Scientists working at the Large Hadron Collider in Geneva may finally have tracked down the elusive Higgs boson. Results announced today at CERN show that a new heavy particle has been identified, with all the properties expected of the Higgs. Bristol physicists working at the CMS experiment played a key role in establishing this exciting new result which is the culmination of twenty years’ work.
“If the Higgs has been finally identified, this will be the biggest discovery in particle physics for forty years,” said Dr Joel Goldstein, leader of the CMS activity in Bristol's School of Physics.
The Higgs boson is the essential connection between the mathematical theory of the Universe, and the everyday world. Without it, the fundamental particles which make up atoms would be massless, completely at odds with what we observe. At a deeper level, the Higgs allows two of the four forces of nature to be treated as one simpler phenomenon, and completes the ‘Standard Model’ of particle physics first proposed in the 1970s.
The search for the Higgs requires the careful study of thousands of trillions of particle collisions at incredibly high energies. The LHC accelerates beams of protons around a 27km ring on the Swiss-French border. On collision, the protons’ energy is converted to new particles, which are detected by a series of huge and complex experiments. From around a billion collisions per second, a Higgs boson is expected to be produced around once per minute – but only a fraction of these can be detected.
Physicists at the University of Bristol have been working since 1993 to build and operate the CMS experiment. Weighing in at around 12,000 tonnes, the experiment is the size of a large building, and is packed with sensitive particle detectors which must operate around the clock. The electromagnetic calorimeter endcap detector, built by a team of physicists from Bristol and other UK universities, has played a vital role in spotting the decay of the Higgs boson to photons, the most important way of finding the new particle. The CMS detector produces 40,000 gigabytes of information per second when operating at full speed. Every byte of data is filtered, processed and then transferred along optical fibres to countries around the world, using equipment and software developed at Bristol.
LHC collision event at CMS showing four high energy muons (CMS Higgs search)
The identification of the new particle is the first step in the LHC research programme, and opens the door to a huge range of possibilities. Physicists will now accumulate much more data in order to carefully measure the properties of the particle – only then can they positively identify it. Many physicists believe that the simplest version of Higgs’ theory must be modified by a new phenomenon called supersymmetry. This would also provide clues as to the origin of the mysterious ‘dark matter’ which occupies the galaxy alongside stars and planets, and would also point the way towards deeper and simpler theories of space and time.
“These new results are a huge achievement, but really represent the first step on a long road of discovery,” said Dr Dave Newbold, head of the Bristol particle physics group. “The really exciting physics is all ahead of us, and it may not turn out to be what we expect.”
The LHC will shut down in 2013 for two years, allowing the equipment which steers and controls the proton beams to be upgraded. From 2015, the accelerator will operate with twice its current energy and three times the number of collisions, putting new discoveries within reach. Work on CMS is carried out in Bristol alongside the study of antimatter at the CERN LHCb experiment, and preparations for future facilities that will allow the Higgs to be ‘mass-produced’ and studied in detail.
Further information
What is the Higgs boson?
The Higgs boson is a type of elementary, sub-atomic particle that is widely believed to play a key role in shaping the way the Universe functions. Confirming its existence is one of the main objectives of the Large Hadron Collider (LHC), which is located at CERN (the European Organization for Nuclear Research) in Switzerland.
Why is the Higgs boson important?
Physicists have developed a theory called ‘the Standard Model’ to explain how the various types of elementary particle that make up the visible Universe interact. With the exception of neutrino physics, results from other particle physics experiments match the Standard Model extremely well - but only if one missing piece, the Higgs boson, is assumed to exist. Based on the particles discovered to date, the Standard Model could not otherwise explain why some particles have mass (e.g. electrons), while others don’t (e.g. photons which make up light). Theoretical physicists believe that the Higgs boson is the key.
So most physicists conclude that another elementary particle must exist – the Higgs boson – and that this gives other particles their mass. In terms of our understanding of matter and the basic forces shaping the Universe, this is a critical issue: without mass, there would be no matter.
How does the discovery of the Higgs boson compare to earlier scientific discoveries?
The search for the Higgs boson mirrors the discovery of the electron. The concept of the electron was first proposed in 1838 to explain the chemical properties of the atom but its presence was not confirmed by British physicist and Nobel prize winner JJ Thompson until 1897.
A century on, the electron’s existence underpins modern science. Manipulating or harnessing phenomena such as electricity, magnetism and thermal conductivity rely on our understanding of the electron – applications include cathode ray tubes (television), radiotherapy treatments for cancer patients, lasers (CDs, energy, manufacturing etc), microscopes, and, of course, particle accelerators like the LHC. Spintronics, the technique of manipulating electron ‘spin’, has the potential to bring us faster computers, increased data storage and more efficient photovoltaic cells.
Our search for knowledge about our Universe continues and it is impossible to determine where it will lead in terms of fundamental knowledge or applications. For example, we do not know why photons, the particles that make up light, have no mass.
JJ Thompson could not have predicted where his discovery of the electron would lead, and similarly we do not know where the discovery of the Higgs boson could lead. Each advance opens up a new frontier of science.
What does the Higgs boson actually do?
It’s believed that Higgs bosons are responsible for determining how much mass other types of elementary particle have. The theory goes as follows: countless numbers of Higgs bosons make up an energy field (‘the Higgs Field’) that extends throughout the Universe. When other types of elementary particle move through the Higgs Field, some do so very easily (like an arrow flying through the air); this results in them having little mass and, in some cases, no mass at all. But other, less ‘streamlined’ types of elementary particle don’t move through the Higgs Field so easily and this results in them having a relatively high mass.
Where does the name ‘Higgs boson’ come from?
Sub-atomic particles are divided into two categories: bosons and fermions. Generally speaking, bosons are force-carrying particles while fermions are associated with matter. The Higgs boson is named after Professor Peter Higgs, a theoretical physicist at the University of Edinburgh. Professor Higgs was one of a number of physicists who predicted the existence of what’s now known as the Higgs boson, which has been dubbed ‘the most sought-after particle in modern physics’. A number of other researchers, including Thomas Kibble of Imperial independently or jointly proposed a similar mechanism, but it has become generally known as the Higgs Mechanism.
How could you ‘see’ a Higgs boson?
You can not directly see a Higgs boson. It’s believed that, with the right experiment in place, a decaying Higgs boson would leave behind a detectable ‘footprint’ in the form of a unique configuration of other particles. Higgs bosons should (according to current theories) be created a few times in every trillion high energy particle collisions at the LHC.
What will happen if it is found?
Confirming the existence of the Higgs boson will provide vital evidence that the Standard Model accurately accounts for how and why energy and matter behave as they do. It would act as a springboard to further research and an improved understanding of the Universe. Ultimately, it may have spin-off benefits in fields as diverse as medicine, computing, electronics and manufacturing.
Discovering the Higgs boson would be the start of a new phase in particle physics – for example, dark matter, which forms 23 per cent of the Universe is not explained in the Standard Model, but the properties of the Higgs boson could point to which extensions of the theory are likely to be correct, setting the direction for particle physics research. Conversely, the properties of the Higgs boson could close off some theoretical options, so particle physics is set for a period of dramatic change if the Higgs is discovered.
Funding
The CMS research programme at Bristol is supported by the Science & Technology Facilities Council (STFC) http://www.stfc.ac.uk/.
