Award of Nobel Prize to Peter Higgs, 2013

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On 8 October 2013, Peter Higgs, Emeritus Professor of Theoretical Physics at Edinburgh University was awarded a Nobel Prize in Physics 'for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider'.

The Higgs boson

The Prize was awarded jointly to Professor Higgs and to the Belgian scientist François Englert, both of whom had helped formulate a theory of how elemental particles achieve mass. In 1964, while working as a lecturer in Mathematical Physics at the Tait Institute, Edinburgh University, Higg published a ground-breaking article which argued that mass was achieved through the existence of a new sub-atomic particle, which became known as the Higgs boson.

Higgs's hypothesis became central to the Standard Model of Physics, a unifying theory of the physical universe. This model posits that the fundamental forces of nature arise from laws of natures called symmetries which are transmitted by particles known as gauge bosons. The symmetry of the weak force should mean that its gauge bosons have zero mass, but experiments show that, on the contrary, they are actually very massive. In 1964, three groups of researchers devised a mathematical model, now known as the Higgs Mechanism, to explain in what circumstances gauge bosons might have mass. This showed that conditions for symmetry could be broken if an unusual kind of field, know known as the Higgs Field, existed throughout space and broke certain laws of the electroweak interaction. Some years later, scientists realized that the same field would also explain why other sub-atomic particles (electrons and quarks) have mass.

For many years scientists had no means of proving the existence of the Higgs Field and thereby showing that the Standard Model was substantially correct. The field could only be verified by finding a carrier particle which would be associated with it: the Higgs boson, a carrier particle which interacted with (and transferred mass to) other particles. This, however, would be very difficult to produce experimentally and would break apart in a minute fraction of a second.

CERN

It took over thirty years to develop colliders, detectors, and computers capable of searching for the Higgs boson. Finally, the development of the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research), Geneva, raised realistic hopes that the elusive particle might be created and detected. The LHC is a 27km circle, 100m beneath the ground, consisting of over 1200 magnets cooled to a temperature colder than outer space. The magnets are used to accelerate protons to fractionally below the speed of light and to smash them together. The collision recreates the conditions that existed just after the Bing Bang when Higgs bosons might first have existed. It was known, however, that the particle would be very rare. Only one in every hundred million collisions was expected to produce a Higgs boson. The Higgs boson would then decay almost immediately, meaning that its existence could only be proved by detecting the particles left by its decay.

ATLAS

Two teams, ATLAS (which included around 20 physicists from the University of Edinburgh) and its friendly rival CMS, were established to analyse LHC data for evidence of the existence of the Higgs boson. By the end of 2011, both teams were seeing tantalising hints that a particle was being created that behaved in the way expected of the Higgs boson. For their observations to be verified, however, around three times as much data would need to be produced and analysed. (By convention, in particle physics, an observation can only be claimed when the chance of misidentification is less than one in 3 million.) By 4 July 2012, both teams had gathered sufficient data for CERN to announce that the existence of a new particle, consistent with the Higgs boson, had been experimentally established. Further work would be needed, however, to analyse its properties and see if these were as predicted by the Standard Model. On 14 March 2013, CERN confirmed that the new particle had + parity and zero spin, two fundamental criteria of the Higgs boson. On 8 October 2013, it was announced that Higgs and Englert would share the 2013 Nobel Prize for Physics. Not owning a mobile phone, and having no other immediate way of being contacted, Higgs only learned that he had won the prize when congratulated by an acquaintance on the street.

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