Higgs Boson Q&A

  • The Higgs boson is a type of elementary, sub-atomic particle. Finding out whether or not the Higgs boson exists was one of the main objectives of the Large Hadron Collider (LHC), which is located at CERN (the European Organization for Nuclear Research) in Switzerland.
     
  • The LHC is the most powerful particle accelerator ever built. Beams of protons or ions are accelerated close to the speed of light and smashed into each other, recreating conditions that existed just after the Big Bang kick-started the Universe around 14 billion years ago. During this first moment of time the particles and forces that shaped our Universe came into existence.
     
  • The Higgs boson is named after Professor Peter Higgs, a theoretical physicist at the University of Edinburgh.
     
  • In particle physics the accepted standard for a ‘discovery’ is 5 sigma – or less than a one in a million chance of this being a co-incidence. By the time researchers collect enough data to reach this level they can also be confident of having ruled out any experimental or systematic errors.
     
  • Two experiments at the LHC (ATLAS and CMS) have been looking for the Higgs boson, using different methodologies - they can be used to check each other’s results, and it is their findings that were announced on July 4th 2012.
     

When was the Higgs boson found?

CERN announced that a new particle had been found, consistent with the Higgs Boson, on 4th July 2012. The scientists involved carried on collecting and analysing data, leading to their confirmation of the Higgs discovery in March 2013, at the Moriond conference.

The results from the ATLAS and CMS detectors, along with previous high energy physics experiments such as LEP and Tevatron, gradually eliminated areas of the energy spectrum where the Higgs boson was expected to exist. By 16 December 2011, results from both ATLAS and CMS pointed to an area of interest in the data in the 125-126 GeV range. Particle physicists focused their attention on this narrow energy range and their findings led to the announcements of the discovery.

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 matched the Standard Model extremely well - but only if one missing piece, the Higgs boson, was assumed to exist. 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 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 mirrored 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.

Over 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 will 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 different 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 predicted the existence of what’s now known as the Higgs boson, which was dubbed ‘the most sought-after particle in modern physics’. A number of other researchers, including Professor 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 cannot directly see a Higgs boson. With the right experiment in place, a decaying Higgs boson leaves 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.

When created in particle collisions at the LHC, the Higgs boson can decay into a pair of ‘Z bosons’, which further decay into other particles. These particles leave a distinctive signature in the ATLAS and CMS detectors that scientists can interpret. However, the same particles are also created in other ways during collisions, so to search for the Higgs, particle physicists were looking for an excess of these particles beyond that predicted as the background ‘noise’.

In particle physics the accepted standard for a ‘discovery’ is 5 sigma – or less than a one in a million chance of this being a coincidence. By the time researchers collect enough data to reach this level, they can also be confident of having ruled out any experimental or systematic errors. This is one of the benefits of having two experiments at the LHC that look for the Higgs boson (ATLAS and CMS) using different methodologies - they can be used to check each other’s results.

What happens now it has been found?

Confirming the existence of the Higgs boson acts 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.

But the Standard Model is not a complete description of fundamental interactions. The discovery of the Higgs is therefore the start of a new phase in particle physics, looking beyond the Standard Model to new theories. These theories, for example, include possible sources of “dark matter”, which forms 23% of the known Universe but is not explained by the Standard Model. Data from the LHC is already advancing knowledge on this front, and a detailed study of the properties of the Higgs boson, and searches for new and exotic particles, will provide vital clues to a deeper understanding of the fundamental nature of matter.

Can we switch off the LHC now?

Definitely not – finding the Higgs is just the start of understanding its properties and implications for particle physics. Also, the LHC has much wider science goals than simply finding the Higgs boson.

How much money has the UK invested in the LHC?

The Science and Technology Facilities Council (STFC) pays the UK contribution to the CERN budget, which is determined on a formula basis related to net national income. The current UK share of the CERN budget is 14.5%, £105M a year. STFC also supports UK participation in the four LHC experimental detector projects.

The UK invested more than £500 million in the construction of the LHC and its detectors, in funding direct to CERN and to the University groups in this country that were involved in the construction and preparation of the accelerator and of the experimental detectors.

Was any of the LHC built in the UK?

The UK has played a major role in the LHC’s design, development and operation, with 15 University groups and the STFC Rutherford Appleton Laboratory involved in the design and construction of the four detectors. At CERN, many key roles are held by UK personnel. UK scientists and engineers have been central to all the major LHC developments, from Professor Higgs’ theoretical work that underpins the research, the initial LHC proposals, detector design and build, day-to-day operation of the LHC, and now data analysis.

During the construction phase of the LHC, CERN spent a significant proportion of its budget with industry. UK industry has played its part in the accelerator project, from construction to the present day – contracts worth £22 million in 2012 alone.

Recent examples include

WS Atkins, winning a contract in September 2013 for more than £300,000 of civil engineering works. Also in September, Centronic were contracted to supply about £600,000 of pressurised ionisation chambers for radiation monitoring. Arcade, a heating and ventilation firm have won several contracts, their most recent in September taking the value to £1million in total.

Gate Informatic is a Swiss company, but a large part of their contract comes to the UK for the supply and maintenance of Network-Attached storage clusters for Oracle real application cluster databases and servers.

How many UK scientists are involved?

The LHC and the experiments run there are large, international collaborations. There are more than 200 UK nationals employed by CERN, of whom more than half are in the scientific grades. In addition, more than 560 UK scientists regularly work at CERN.

Key UK CERN personnel include:

  • Sir Christopher Llewellyn Smith FRS, Director-General of CERN (1994-1998)
  • Roger Cashmore, CERN Deputy Director General (1999-2003)
  • Dr Lyn Evans – LHC Project Manager (1994-2010)
  • Jim Virdee, Spokesperson of CMS (2006-2010 and deputy (1993-2006)
  • John Ellis, CERN Division leader Theory
  • Dr Steve Myers – CERN Director of Accelerators and Technology
  • Dr Paul Collier, CERN Head of Beams Division
  • Ian Bird – CERN LHC Computing Grid Project Leader
  • Dave Charlton, Spokesperson of ATLAS

Science and Technology Facilities Council Switchboard: 01793 442000