Finding the God particle: Understanding Higgs Boson

Recently the discovery of Higgs Boson made a great splash on the world media and everyone seemed very excited about something that is so remote from our daily life, that the rest of us were left incredulous about it.

In school, we all learn to define mass as a measure of the ‘inertia’ of a body, and understand the ‘inertia’ to mean the innate resistance of a body to any change in its state of movement (of which rest is a special case). We also learn that Newton taught us that the force is equal to the mass times the acceleration of a body. The question is, why do we resist change in movement? Why is there a difference between the amounts of force required to make different bodies move? For a long time scientists have been postulating that there is something very fundamental about this resistance to change in state of motion but have not been able to pin it down. Now they have.

Let me take an analogy. If you walk on land it is easier than walking in water—clearly our inertia—for the same mass is different depending on the surrounding medium. So physicists postulated that even when we think there is vacuum, there is some ‘field’ pervading the Universe and when we move, this field resists our movement—like water particles that resist our movement in water. 

Professor Peter Higgs and his colleagues gave us a mathematical formulation under which this could be described in great detail. The field is called Higgs field.

But to go back to our analogy, the additional resistance we feel in water is because water particles are dense and hard to push. The similar particle of Higgs field was the Higgs particle. But the exact nature of the Higgs particle was not known and hence the detailed properties of this field that we experience as resistance to motion were not understood. It is like a fish in the sea not being aware of the water molecule. Once the fish knows the water particles and its properties, it will understand why hot water is easier to swim and when and why does water freeze at a certain time. It can then go on to study the relation between sunlight and the resistance it faces while swimming and so on. Just as a round or flat fish faces more resistance than a streamlined fish—a body which sticks more with the Higgs field will face greater resistance in the Higgs field and hence will have more inertia. Simple.

Higgs boson is this proverbial water molecule of the Higgs field—like water molecule of ‘sea field’.

So experimenters have been working hard to isolate these Higgs particle so that we can study them. The problem is that the Higgs particle is very heavy and lives for such a short while that it is not easy to separate it out. In fact the amount of energy needed to isolate a Higgs particle is so large that we had to employ one of the largest accelerators ever built to isolate it—to temporarily extract it from its field and have a quick look at it before it disintegrates into other known particles.

CERN achieved it and Prof. Higgs (together with a Belgian colleague called Prof. Francois Englert) got the Nobel Prize for predicting the existence of Higgs field and the Higgs particle. So how come the people who discovered it did not get a Nobel Prize? Well, that is because from various other studies scientists had a suspicion that the mathematical formulation that Higgs gave was probably correct. But we did not have the exact idea of its mass. We had never held it and observed it. CERN did this for us. It determined the exact mass of this Higgs particle. But the experimenters were not awarded a Nobel Prize, this time probably because the ATLAS and CMS Experiments at CERN that made the measurements are huge team efforts without any person whom you could specify as the real leader. Alfred Nobel’s will does not allow the giving of the Physics prize to an organisation—it specifically mentions individuals. In 1982 on the other hand, the Nobel committee did give the prize to Rubbia and van der Meer, who in 1982 discovered the W and Z bosons—which had been predicted as far back as 1961 and were on pretty solid theoretical ground by 1973.

So what next? Well, we can continue to use the simile of the fish in water for world in Higgs field. Now that we know what is the exact nature of this particle that is giving us resistance we can look at it in detail. We can start asking questions like why is the resistance to Higgs Field exactly identical to the pull of gravity—why is our inertia same as our mass? We can also look for other properties of Higgs field—its relation to formation of the Universe—to the formation of fundamental particles and so on. We can also start worrying about the Higgs field and the birth of the Universe and its relation to other aspects of the Universe. 

Like a fish that has learnt that water molecules make up the water in which it swims, we now have a vast new perspective about the Universe and start to study it in considerably more detail. 

This is the reason why the scientists were so excited when they found the Higgs particle and held it in their technology based ‘hands’. So what does this Higgs look like—well it is heavy about 133 times as heavy as a hydrogen atom—that is heavy as far as fundamental particles go. It is also a ‘boson’. This defines some of its basic properties—at the simplest level it means that two Higgs particles can sit together without fighting—as opposed to the other particles called ‘fermions’, two of which cannot be in the same state. The Higgs field is also unique in another way. If we move at constant velocity, we do not experience any resistance! All this and more is now amenable to studies and science is richer for it.

So if you are a physicist working on fundamental physics these are exciting times. 

(The author wants to thank Prof. Sreerup Raychaudhuri of TIFR for going through the manuscript and ensuring that it is scientifically correct)

Dr Mayank Vahia is a scientist working at the Tata Institute of Fundamental Research since 1979. His main fields of interest are high-energy astrophysics, mainly Cosmic Rays, X-rays and Gamma Rays. He is currently looking at the area of archeo-astronomy and learning about the way our ancestors saw the stars, and thereby developed intellectually. He has, in particular, been working on the Indus Valley Civilisation and taking a deeper look at their script.