The Most Significant Physics Breakthrough of 2012


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The ATLAS experiment at CERN – visualizing two protons colliding. Image by CERN

Selecting the top story in physics is difficult most years, but for 2012 there is no contest. The discovery of a “Higgs-like” particle at CERN’s Large Hadron Collider is the clear winner.

Higgs is number one on most everyone’s list and arguably the greatest scientific discovery in the 21st century to date.

Higgs and the Standard Model

We have observed a new particle consistent with a Higgs boson,” CERN director general Rolf Heuer announced to the world on July 4, 2012. Data from two independent teams showed that the particle had a mass of around 126 GeV (gigaelectron volts) – about 130 times the mass of a proton.

So what’s the big deal? The standard model of quantum mechanics – the most accurate and all-encompassing theory in the history of physics – predicts that all known matter in the universe is made up of 25 fundamental particles.

With the discovery of the top quark in 1995, experimental physicists had found all but one. The only particle missing was the Higgs boson – the one that explains why particles have mass.

All particles are bundles of energy and a momentum of quantum fields. The quantum field that produces the Higgs boson is called the Higgs field – proposed in 1964 by three independent groups of physicists and named after one of the researchers, English physicist Peter Higgs.

The Higgs field has been likened to a great invisible ocean that permeates all of space. Some particles, like photons (light particles) and gluons (nuclear force particles), do not interact with the Higgs ocean at all. So they have zero mass and travel through space at the maximum speed possible: the speed of light. Other particles, like electrons and quarks, do interact with the Higgs field – the more they interact with it the more mass they have. And because they have mass, they can never reach light speed.

Mass is a measure of an object’s resistance to being accelerated. The more massive the object, the harder it is to speed it up or slow it down. So when a particle with mass travels at a constant speed, there is no Higgs effect. It is only when it tries to change speed that the Higgs ocean comes into play.

Large Hadron Collider: Looking for the Higgs Boson

At the Large Hadron Collider, electric fields accelerate protons (which are made up of three quarks) through a 17-mile ring-shaped subterranean tunnel, nearly reaching the speed of light. Magnetic fields steer the photons in opposite directions through the tunnel to meet and collide head-on. Experimenters then look for traces of the Higgs particle in the collision debris.

Physicists cannot see the Higgs boson directly. As CERN explained in its Atlas News, “The Higgs Boson is an unstable particle, living for only the tiniest fraction of a second before decaying (transforming) into other particles. So experiments can observe it only by measuring the products of its decay.

Using this method, the ATLAS and CMS teams evaluated data from hundreds of trillions of proton-proton collisions. They arrived at the same conclusion: a new particle has been found and it is a boson – a particle with integer spin (a measure of a particle’s angular momentum).

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