A matter of understanding: In Search of the Higgs boson (the God Particle)

Nick Dallas investigates the Greek contribution to the recent discovery of the Higgs boson - alternatively known as the God particle

In July of this year, CERN (European Organisation for Nuclear Research) scientists reporting from the Large Hadron Collider (LHC) in Geneva claimed discovery of a new sub-atomic particle consistent with the Higgs boson, often dubbed the ‘God particle’. Champagne corks were popping in physics labs across the globe as physicists were overcome with emotion having reached this milestone event after a 45-year hunt.

However, one needs to take a step back to understand both the significance and complexity of these developments. Most importantly the discovery provides vindication for the so-called ‘Standard Model’ of physics which envisages that the known universe is made from twelve basic building blocks (a class of fundamental particles called fermions) and governed by four fundamental forces which are mediated by another set of particles called bosons. The Standard Model has been the reigning theory of particle physics for the last half century.

Every particle predicted by the Standard Model had been discovered with only the Higgs boson remaining elusive, until now. It has long been sought, for it is considered the key in resolving the mystery of how the universe began. The Higgs boson is associated with the Higgs field, an invisible field theorised to pervade the universe. As particles travel through this field they acquire mass proportional to the strength of their interaction with the field. The Higgs field together with the Higgs mechanism allows us to understand how particles attain mass.

Everything would be massless without such a mechanism in operation. It is believed that after the Big Bang, many particles had no mass but started to acquire mass as they interacted with the Higgs field which has the Higgs boson as its signature particle. The Higgs boson is named after Peter Higgs, an Edinburgh University physicist who proposed the existence of a particle that confers mass in a research paper published in 1964. It was mischievously named ‘the God particle’ by Nobel prizewinning physicist Leon Lederman.

Higgs himself is uncomfortable with this label not only because he is not a believer himself but is also conscious that the misuse of terminology might offend some people who are religiously inclined. Others may argue that the term ‘God particle’ is not misconstrued at all. In fact, it is one of the rare occasions where often publicity-shy scientists have been media-savvy and on the front foot.

If one considers the information age we live in, where we are bombarded with updates on the latest exploits and misdeeds of media and sports celebrities: the public’s attention span on science is in the near-zilch category. All this fanfare about the Higgs boson discovery would not have been possible without the existence of the LHC, the world’s largest and most powerful particle accelerator.

Lying in a tunnel 27 kilometres in circumference and as deep as 175 metres beneath the Franco-Swiss border, it took fifteen years to build, cost $10billion and required the collaboration of over 10,000 scientists and engineers from more than 100 countries. The LHC has around 9,600 magnets installed to steer protons travelling at fractionally under the speed of light. Some of these superconducting magnets are cooled to 1.9 Kelvin (-271° Celsius) using 10,800 tonnes of liquid nitrogen and a further 120 tonnes of liquid helium to eliminate any electrical resistance. Temperatures in excess of 100,000 times hotter than the centre of the Sun can be generated, a mere 1.6 trillion degrees Celsius, whilst up to 600 million collisions per second can occur.

At these temperatures ions melt into a quark-gluon plasma concoction, a state of matter believed to have existed at the onset of the Big Bang. Quarks and gluons are constituents in the Standard Model. To sample and record the results of these collisions, four gargantuan detectors have been positioned along the circular track. Meanwhile tens of thousands of computers across the globe are linked in a distributed network and used to analyse the 15 million gigabytes of collision data produced from LHC experiments annually.

By examining these collision trails and measuring certain properties like the speed, mass and electric charge of particles and their fragments, it is possible to work out the identity of a particle. Presently the LHC has achieved record proton smash collisions of 8 TeV (8 x 1012 electron Volts) but has a design capacity of 14 TeV. Such high energies are essential in detecting Higgs bosons. The LHC is truly a paradigm of international collaboration in physics as more than 7000 scientists from 85-plus countries are involved in the LHC and its six experiments. Two of the experiments involve the ATLAS and CMS general purpose detectors where there’s been a significant contribution from Greek physicists. Greece was one of the twelve founding member states of CERN in 1954 and Cyprus has recently become an associate member.

Greek institutes have participated in the design, construction and commissioning of the barrel muon systems of ATLAS and of the pre-shower detector and data acquisition system of CMS. A team lead by Professor Charikleia Petridou of the Aristotle University of Thessaloniki has built part of ATLAS’s muon spectrometer, a key device in detecting the Higgs boson. Kavala-born Professor Petridou worked at CERN for ten years before returning to Greece in 1995. She has played a leading role in Greece’s LHC involvement and is a passionate campaigner for science education. Another key Greek physicist, has been the enigmatic Professor Maria Spiropulu, considered one of the rising stars of high energy particle physics.

As a young girl growing up in Kastoria she dreamed of being an F-16 fighter pilot, then an astronaut, but finally finished up as an experimental physicist. After graduating from the Aristotle University of Thessaloniki, she completed her physics PhD at Harvard working at Tevatron in Chicago, which was the world’s most powerful particle accelerator before the LHC was commissioned. Presently she is involved with the CMS experiment at CERN while concurrently lecturing at Caltech (California Institute of Technology).

By being able to recreate and imitate the primordial particle soup associated with our universe’s birth pangs, the arrival of the LHC has ushered in a new era for physics research. LHC experiments may reveal the nature of dark matter, which is thought to hold galaxies together. The existence of super-symmetry, the nature of black holes and whether there are spatial dimensions beyond the familiar three known to exist will be on the research agenda for years to come. For Greek physicists, this represents an opportunity to not only carry out some cutting edge research but also collaborate at the highest international levels in particle physics. In the past they have shown that they can match it with the world’s best given the chance.

The present Greek crisis will no doubt put the nation’s science research funding and CERN involvement under the microscope. As always, the most talented will seek their fortunes abroad and continue the accustomed brain drain: an all too familiar haemorrhaging of Greece’s brightest. It will also be a pity if the uncertainties and strains brought about by Greece’s current predicament dissuade students from choosing scientific career paths at a time when research possibilities exist in unlocking the universe’s mysteries.

Further reading:

Leon Lederman and Dick Teresi, The God Particle: If the Universe Is the Answer, What Is the Question?, Mariner Books, New York, 2006.

Ian Sample, Massive: The Missing Particle That Sparked the Greatest Hunt in Science, Basic Books, New York, 2012.

Jim Baggott, Higgs: The Invention and Discovery of the ‘God Particle’, Oxford University Press USA, new York, 2012.