Tribute to Peter Higgs
Tribute to Peter Higgs
The doyen of particle physics and Nobel prize winner Peter W Higgs passed away on 8th April 2024. Peter Higgs is best known for ‘Higg’s Boson’, which in popular culture is known as ‘the God particle’.
Higgs Boson is one of the greatest discoveries in the last 100 years. By proposing the existence of this particle, Peter Higgs earned his position among the giants of modern physics like Albert Einstein and Stephen Hawking.
Peter Higgs was born on 29th May 1929 to an English father and a Scottish mother. His father was a sound engineer with BBC. He studied at King’s College London, gaining a PhD in theoretical Physics in 1954. He then joined the university of Edinburgh at the Scottish capital. He continued to do research and teaching at Edinburgh till he retired in 1996.
What Peter Higgs did was to solve a finely fundamental problem in Physics; how do fundamental particles acquire mass? The standard model of particle physics explains how fundamental particles interact with each other and constitute the universe as we know it. As per this model, matter is made of quarks and leptons. There are six types of quarks; up, down, charm, strange, top and bottom. Electrons, muons, I-particles and the three types of neutrinos (electron neutrino, muon neutrino, and the I-neutrino) form the family of leptons.
There are four fundamental forces through which the fundamental particles interact with each other; (i) gravitational, (ii) electro-magnetic, (iii) weak, and (iv) strong forces.
The strong force binds the quarks to form protons and neutrons, and the residual strong force binds protons and neutrons together into nuclei. The electro-magnetic force binds nuclei and electrons together forming atoms. The same force binds atoms together to form molecules. The gravitational force is responsible for the formation of large scale structures like planets, stars and galaxies. The weak force is the cause for certain kinds of nuclear decay.
The fundamental forces manifest through the exchange of mediating particles. The particles that mediates the electromagnetic force is the photon. For gravitational force we have the graviton and for the weak force the mediating particles are the W+, W-, and Zo particles. The strong force is mediated by gluons.
The standard model of particle physics is a remarkably successful theory. It is supported by experimental verifications with high accuracy. But in its formative years the theory could not explain how fundamental particles came to have mass and why different particles had different masses.
In the early 1960s physicists started modelling the behavior of fundamental particles using equations of quantum mechanics. The found that these equations had perfectly symmetric pattern if the fundamental particles were treated as massless. When the equations were modified by introducing the masses of the particles, the symmetry was spoiled and the equations became complex and inconsistent.
Peter Higgs came up with a path-break idea to solve this problem. He kept the equations symmetric by not arbitrarily introducing the particle masses. Instead, he proposed that all space is filled with a scalar field, the Higgs field. He then proposed a mechanism, whereby the fundamental particles interact with the Higgs field and acquire mass. It was suggested that different particles have different couplings to this field and hence they acquire different masses.
In 1964 Peter Higgs published his magnificent ideas in a research paper in Phy. Review Letters. Higgs ideas were not accepted by the scientific community immediately, but over the years scientists started seeing the merits of his theory.
The proposed Higgs field is an all pervading scalar field. The vibrations of this field should produce a particle which we now call the Higgs Boson. It is a boson because it is a spin zero particle. Theoretical calculations showed that Higgs boson itself has mass and it decays into certain other fundamental particles.
It took the scientific world almost half a century to experimentally locate Higgs Boson, and hence to confirm Higgs theory. Fundamental particles are produced and studied in the laboratory by the collision between particles accelerated to very high energies. To make collisions which can lead to the formation of Higgs bosons, we need to accelerate the colliding particles to extremely high energies. Such particle accelerators were not built till the early decades of the 21st century.
Active search for Higgs Boson started with LEP experiments at CERN in the 1990s and the Tevatron experiments at the Fermilab in the 2000s.
The European centre for Nuclear Research – CERN is an establishment collectively funded by European nations. Its main focus is on fundamental research in parcel physics. Fermilab is the premier particle physics laboratory in the United State.
Collided the particles at energies that reached upto 209 GeV. At Fermilab the Tevatron guided beams of protons and anti protons to the TeV range of energies before they collided. These collisions produced an array of particles which were studied extensively. Both LEP and Tevatron experiments could not observe the elusive Higgs boson, but they produced large amount of useful data which narrowed the search for Higgs boson.
In 2008 CERN commissioned the Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator. The LHC consists of a 27km circumference ring of abour 9000 superconducting magnets. This is an underground structure beneath Switzerland and France. Inside this circular structure two separate beams of protons travel in opposite directions at close to the speed of light. The beams are made to collide at four different locations around the accelerating ring, corresponding to the positions of four particles detectors; ATLAS, CMS, ALICE, AND LHCb.
One of the chief motivations of building such a gigantic particle accelerator and the detectors at CERN was to observe the Higgs boson among the products of the numerous proton-proton collisions. That would be a direct experimental verification of the theoretical foundations of modern particle physics.
Mathematically, the idea of Higgs field was elegant. It heavy particles like protons at extremely high energies are made to collide, then the disturbances in the Higgs field should produce a particle, the Higgs boson. This will be one among the many particles produced by these collisions. Higgs boson being unstable will almost instantly disintegrate into other particles. The trajectories of these particles can be traced and analyzed.
The historic moment came in 2012. At CERN’s Large Hadron Collider, scientists at the ATLAS and CMS detectors analysed the products of large number proton-proton collisions at 8 TeV energy. They found strong evidence for the Higgs boson with a mass of about 125GeV. On July 4th, 2012 the CERN scientists officially announced the observation of Higgs Boson.
A year later, in 2013 Peter Higgs was awarded the Nobel prize for physics. He shared the prize with Belgian Physicist Francois Englert. Englert had independently proposed the theory of Higgs field in 1964 along with his cowokers.
The successful validation of the Higgs field and the experimental observation of Higgs boson is a wonderful example of how elegant mathematical formulations indeed describe physical reality.
