Discovery of the Higgs boson

A new look at our world

Science and techno world topic: Physics

Speaking before a crowded auditorium Wednesday, July 4, the Director General of CERN Rolf Heuer has confirmed that two separate teams who worked on the Large Hadron Collider (LHC) are virtually certain to have discovered the Higgs boson, or as has been called the "God particle". Or at least, a particle entirely new exactly where we expected it to be the Higgs boson.

Picture: An artistic representation of a Higgs boson that emerges from a collision between protons.

It was the main purpose of the LHC, the giant particle accelerator built underground on the border between Switzerland and France: experimental search for traces of the particle that, according to the Standard Model of physics, explain why all objects in our universe have mass, and therefore, ultimately, the explanation why there are galaxies, planets and even humans. For this reason, the Higgs has been dubbed, somewhat 'emphatically, "the God particle." Peter Higgs, an English physicist who gave his name to the Higgs, was present at the press conference in Geneva, together with four other scientists who collaborated with him in the sixties to develop the theory. 

"Our data show clear signs of a new particle whose mass is in the region around 126 GeV," said Fabiola Gianotti, ATLAS spokesperson of the experiment. The GeV (gigaelectronvolt) is a unit of energy in particle physics is also used to measure the mass using the conversion to the famous equation of relativity E = mc ².

"The results are preliminary, but the signal at around 125 GeV is clear," continued Joe Incandela, a spokesman for CMS, another ongoing experiment at the LHC. "It really is a new particle. We know that to be a boson and boson is the heaviest ever observed. The implications are very significant and for this we must be extremely diligent in future searches and cross-checks."

The two research teams have worked in complete independence: neither of them knew the work presented by the other group. Both have reached the threshold of safety that sigma 5 (5 standard deviations, equal to a probability of 99.99995 percent). This means that there is only one chance in a million that the observed signal is the result of a fortuitous statistical fluctuation.

"It's hard not to be excited about these results," is the comment of Sergio Bertolucci, director of research at CERN. "Last year we had agreed that if by 2012 we had not found a new particle similar to that predicted by Higgs, we could exclude the existence in the standard model. While adopting all the necessary caution, it seems to me that we are at a turning point. “

While talking about achievement "historic," Heuer has long warned about the work that awaits physicists to confirm the identification of the particle and further test its properties. Although both teams are confident that the new particle has the expected mass for the Higgs boson, still need to determine if it behaves as expected and what is its role in the origins and existence of the universe.

"We should all be very proud of this moment, but we're just beginning," says Heuer.

"The next step," the official statement of the specific CERN, "will determine the precise nature of the particle and its significance in our understanding of the universe. Its properties are exactly those theoretically expected for the Higgs boson, the missing piece in the Standard Model of particle physics? Or is it something more exotic? The Standard Model describes the fundamental particles that compose all objects visible universe - including human beings - and the forces acting between them. But apparently the visible matter represents only 4% of all that is in the universe. If it proves a more exotic version of the Higgs boson, the new particle might help us to understand that 96 percent of ' universe that remains obscure. "

The missing piece

Higgs and his colleagues theorized the existence of the Higgs to explain why some subatomic particles, like electrons or quarks have a mass, while others, like photons, lack it. According to Higgs the entire universe would be surrounded by an invisible field, similar to a magnetic field, the one called the Higgs field. Each particle interacts with this field in different ways: if it moves within the field without relevant interactions, will not be provided with mass; more these interactions are, the greater it’s mass.

Photo: Physicist Peter Higgs: For 40 years, physicists have been searching for the Higgs boson.

The idea assumes that there is a particle associated with the Higgs field: the Higgs boson, in fact. According to the Standard Model, if the Higgs field does not exist, the universe would be very different, says Michael Peskin, a theoretical physicist at the National Accelerator Laboratory at Stanford University. "It would be very difficult to form atoms. So the world we know, in which matter is made of atoms, and electrons combine to form chemical bonds, could not exist without the Higgs field."

In other words, there would be no galaxies, no stars, no planets, no life on Earth, of course.

The teasing nature

Buried beneath the French-Swiss border, the Large Hadron Collider is essentially a tunnel 27 km long oval. Inside, proton beams are accelerated to a speed slightly less than that of light and then collide using magnetic fields.

In these battles high energy fundamental particles create "exotic", some of which, in all probability, have existed in nature only in the moments immediately after the Big Bang. These particles have very short life - very few fractions of a second - before decaying into other particles. So far the theory predicted that the Higgs boson would have had life too short to be observed directly, but it would be possible to detect particles generated from its decay.

The results announced in Geneva explain why hunting is so long and difficult. The new particle mass (125-126 GeV) is too high to be detected by the older generation of accelerators, lower-energy: as the LEP (Large Electron-Positron Collider), the predecessor of the LHC at CERN, which could only detect masses up to 115 GeV approximately.

On the other hand, a particle of 125 GeV, decaying, does not produce particles so unusual to be proved beyond doubt its existence. Apparently, the decay of the Higgs particle gives rise to relatively common, such as quarks, already produced millions of LHC.

"Well, it turns out that nature has been very naughty with us," says David Evans, a leading English team working on ALICE, another experiment of the LHC. "The mass range within which, we discovered, is the Higgs boson is what makes it more difficult to find."

To Giannotti, however, it is also a happy coincidence: "If the Higgs boson has the mass, it means that here at the LHC can detect it in many different final states. So we must thank nature."

The hunt continues

Even if the Higgs hunt was the main objective that led to the construction of the LHC, scientists work does not stop here. First, the data must be organized early in Geneva, reviewed by the scientific community and presented in the form of article for a magazine.

In addition, in the coming years we will have addressed other outstanding issues: for example, into which other particles are transformed when the Higgs decays. All this will serve to determine if the new particle behaves exactly like the one provided by the Standard Model.

ATLAS and CMS are also only two of the four main LHC experiments hosted by. The other two, ALICE and LHCb, are facing more fundamental problems of physics: for example the prevalence of matter over antimatter in the universe.

"To make a comparison with the Olympics, to find the Higgs boson is a little 'how to win a gold medal," said Evans. "But of course each country wants to win more than a medal, and I think that CERN will take home over the next several years."