Long-sought Higgs particle probably found, scientists say

The white circle marks where the tracks of the Large Hadron Collider lie underground. (Courtesy CERN).

Scientists at the European Laboratory for Particle Physics, CERN, near Geneva announced on Wednesday that a particle fitting the correct description had been found, though there remains the unlikely possibility it is a misidentification.

"We have reached a milestone in our understanding of nature," CERN director general Rolf Heuer said. "The discovery of a particle consistent with the Higgs boson opens the way to more detailed studies... which will pin down the new particle's properties, and is likely to shed light on other mysteries of our universe," he added.

The final building block

The Higgs boson is the final building block that has been missing from the "Standard Model," a working picture of nature that mainstream physicists rely on and that describes the structure of matter in the universe. The Higgs boson combines two forces of nature and indicates that they are, in fact, different aspects of a more fundamental force. The particle is also responsible for the existence of mass in elementary particles - the quality we feel as weight.

Physicists have been hoping for an overarching theory of nature that can unify the four basic forces known in the universe: the weak force responsible for radioactivity; the electromagnetic force; the strong force responsible for the existence of protons and neutrons, the core of the atom; and gravitation.

The first step in the journey to unify the forces would be completed with the discovery of the Higgs particle: the union of two elementary forces - the electromagnetic and weak force, to become the "electroweak" force. One aspect of the Higgs boson, named after the Scottish physicist Peter Higgs, manifests itself in the giving of mass to the carriers of the weak force, known as "W" and "Z" particles.

Almost the speed of light

In the effort to discover the Higgs boson, unify the fundamental forces and understand the origin of mass in the universe, scientists built the world's largest machine. It's a particle accelerator nestled in a 27km long circular tunnel, 100m beneath the border between France and Switzerland, in the European particle physics laboratory, CERN, near Geneva.

This accelerator, the Large Hadron Collider, speeds up beams of protons, subatomic particles in the core of the atom, up to 99.999998% (the speed of light is 300 000km/second) the speed of light - that means the particles are travelling at a speed of 299 999994km/second. According to Einstein's theory of relativity, this increases their mass by 7 500 times. The accelerator aims the beams straight at each other, causing collisions that release so much energy, the protons themselves explode. For much less than the blink of an eye, conditions similar to those that existed in the universe in its first fraction of a second are found in the accelerator.

As a result, particles of matter are turned into energy, in accordance with Albert Einstein's famous equation describing the conversion of matter into energy: E=mc2. The system then cools back down, and energy turns back into particles.

Data analysed from a thousand trillion proton collisions

The collisions produce energetic particles, some of which exist for extremely short periods of time. The only way to discern their existence is to identify the footprints they leave behind. For this purpose, a variety of particle detectors were developed, each optimized for capturing particular types of particles.

The scientists analysed data from a thousand trillion proton collisions. In these, Higgs bosons are expected to arise along with many other similar particles. Evidence to suggest the existence of the Higgs arises through searches for anomalies in the collected data in comparison with the expected data if such a particle does not exist. This search focuses on the estimated mass of the particle: 126 trillion electron volts (Gev), the units of mass used for atomic-scale particles. When the scientists do manage to find such anomalies, they must then rule out the possibility that it is due to statistical fluctuation.

The calculations carried out by scientists in recent weeks have revealed, with a high degree of statistical significance, a new particle with a mass similar to the expected mass of the Higgs, the researchers announced. Their wording is purposely cautious, leaving room for the possibility that a new particle other than the Higgs can be found within this mass range.

The biggest day of my life'

The probability that this is, indeed, another particle, is quite low, they added, but if that does turn out to be the case that could point to some interesting scientific possibilities in its own right. "We stated last year that in 2012 we would either find a new Higgs-like particle or exclude the existence of the Standard Model Higgs. With all the necessary caution, it looks to me that we are at a branching point," said CERN research director Sergio Bertolucci.

"This is the biggest day of my life," said physicist Eilam Gross of the Weizmann Institute of Science in Rehovot, Israel, a senior member of the international scientific team involved in the research. "I have been searching for the Higgs since I was a student in the 1980's. Even after 25 years, it still came as a surprise. No matter what you call it - we are no longer searching for the Higgs but measuring its properties."

Source: Weizmann Institute of Science, CERN and World Science World Science Net