As elementary school students we learn that all matter is made of atoms. Later, we learn that atoms are made of protons, neutron and electrons. If we are lucky perhaps even later in school we learn that protons and neutrons are made of even smaller particles called quarks. Unfortunately, this is where, for most of us, our education about the fundamental nature of the stuff around us ends. Physics’ standard model (pictured to the left) for the structure of matter tells us that matter consists of a small number of particles (six quarks, six leptons, five gauge bosons). Until yesterday, one particle had been predicted for several decades and not yet discovered – the Higgs boson.
Official news from Europe came in the wee hours of the morning of Wednesday, July 4th. The Higgs boson had been discovered independently and conclusively by two teams, both working at CERN’s Large Hadron Collider. The discovery met the particle physics criteria of a five sigma detection threshold, meaning that there is less than a 1 in 1 million chance of the evidence being a statistical fluke - for comparison the chance of you being struck by lightning this year is greater than that. Physicists around the globe partied like it was 1999. Why such excitement from a typically sedate group?
To give a scientific answer - the Higgs boson is the predicted manifestation of a theory that provides an explanation for why elementary particles have mass. The idea put forward by Peter Higgs (below) and five other scientists in the 1960s was that space is filled with a field that impedes the motion of elementary particles. This interaction between the particle and the field is what gives the particle mass. The theory goes on to predict that if this field exists, then a massive, very short-lived particle (the Higgs boson) must also exist. The discoveries in the 1990s of the W and Z bosons predicted by a related theory gave further credence to the elusive particle’s existence. Now we have word that the proton collisions at CERN have produced the Higgs boson. The search for the Higgs boson was the primary reason for building the Large Hadron Collider – it was just out of reach of the less powerful Tevatron at Fermilab in the United States that ceased operations last year due to budget cuts. The investigation of this particle’s specific properties, which will be studied at CERN for the next several years, has the potential to bring an even deeper understanding of the underlying principles that govern our universe.
There are still a number of questions left to be answered. Our understanding of the contents of our universe is still incomplete. The Higgs does not shed light on dark matter that is needed to hold galaxies together nor does it explain dark energy which is causing our universe to accelerate in its expansion. There is perhaps a sixth boson still to be discovered that carries gravitational force between particles – the graviton. The answers to these and other mysteries are discoveries for another day.
Today, thanks to this discovery of the Higgs (the picture below shows the ATLAS detector one of the two detectors involved in the Higgs discovery), physicists celebrate a more certain vantage point from which to explore the structure of matter and the nature of our universe. Many alternative theories can now be rejected and new theories will be guided and constrained by observations of the Higgs. To further understand the excitement for the Higgs boson, consider the impact made by the discovery of the electron in 1897. That discovery ushered in an explanation for the structure of the atom, the periodic table of elements, and a new way of understanding chemistry. Subsequent work led to the development of cathode ray tubes, transistors, and computer chips. The electronic revolution that has changed our way of life over the past century flows from the discovery of the electron. What leap of understanding might result from the discovery of the Higgs boson?