Most people think they know what mass is, but they understand only part of the story. For instance, an elephant is clearly bulkier and weighs more than an ant. Even in the absence of gravity, the elephant would have greater massâ€”it would be harder to push and set in motion. Obviously the elephant is more massive because it is made of many more atoms than the ant is, but what determines the masses of the individual atoms? What about the elementary particles that make up the atomsâ€”what determines their masses? Indeed, why do they even have mass?
Unlike protons and neutrons, truly elementary particlesâ€”such as quarks and electronsâ€”are not made up of smaller pieces. The explanation of how they acquire their rest masses gets to the very heart of the problem of the origin of mass. The account proposed by contemporary theoretical physics is that fundamental particle masses arise from interactions with the Higgs field. A key player in physicistsâ€™ tentative theories about mass is a new kind of field that permeates all of reality, called the Higgs field. Elementary particle masses are thought to come about from the interaction with the Higgs field. If the Higgs field exists, theory demands that it have an associated particle, the Higgs boson. In short, this Higgs particle becomes the source of all
mass. Using particle accelerators (giant machines such as LHC), scientists are now hunting for the Higgs. Scientists are studying Higgs particle for not only it is important but it's existence is directly related to our existence in this universe.
The Higgs boson is named after Peter Ware Higgs (born 29th may 1929), a British theoretical physicist, who was one of six authors in the 1960s who wrote the ground-breaking papers covering what is now known as the Higgs mechanism and described the related Higgs field and boson.
On 4 July 2012, the two main experiments at the LHC (L
ollider), ATLAS (A T
) and CMS (C
olenoid), both reported independently the confirmed existence of a previously unknown particle with a mass of about 125 GeV/c2
(about 133 proton masses, on the order of 10-25
kg), which is "consistent with the Higgs boson" and widely believed to be the Higgs boson. They acknowledged that further work would be needed to confirm that it is indeed the Higgs boson and not some other previously unknown particle (meaning that it has the theoretically predicted properties of the Higgs boson) and, if so, to determine which version of the Standard Model it best supports.
One possible signature of a Higgs boson from a simulated protonâ€“proton collision. It decays almost immediately into two jets of hadrons and two electrons, visible as lines.
Finally found (Image: Thomas McCauley/Lucas Taylor/CERN/CMS Collaboration)
There's a 5-in-10 million chance that this is a fluke. That was enough for physicists to declare that the Higgs boson â€“ the world's most-wanted particle â€“ has been discovered. Rapturous applause, whistles and cheers filled the auditorium at CERN, near Geneva, Switzerland.
Almost 50 years after its existence was first predicted, the breakthrough means that the standard model of particle physics, which explains all known particles and the forces that act upon them, is now complete.
A Higgs boson with a mass of around 125 to 126 gigaelectronvolts (GeV) was seen separately by the twin CMS and ATLAS detectors at the LHC, each with a confidence level of 5 sigma, or standard deviations, the heads of the experiments announced today at CERN.
Even by particle physicists' strict standards, that's statistically significant enough to count as a particle discovery.
"I think we have it," said Rolf Heuer, director general of CERN, as he concluded a hotly-anticipated seminar.It's elementary
The Higgs boson gives all elementary particles mass, allowing for the existence of matter. It is the fundamental unit, or quantum, of the Higgs field, an all pervading entity that all particles must pass through. Some, like the photon, slip through unhindered â€“ they are massless. Others, though, must struggle like a fly trapped in treacle. The Higgs and its field are required by the standard model, but had never been conclusively detected before today's report.
The seminar was full of emotion and elation. An emotional Peter Higgs, who postulated the boson that is his namesake in 1964, wiped a tear from his eye as the teams finished their presentations in the Cern auditorium. "I would like to add my congratulations to everyone involved in this achievement," he added later. "It's really an incredible thing that it's happened in my lifetime."
"This is an important result and should earn Peter Higgs the Nobel Prize," Professor Stephen Hawking told BBC News.
There was also some humour: "It is very nice of the standard model boson to be at that mass," says Gianotti. "Because of that mass we can measure it. Thanks nature."
The physicists were a little reticent to call the discovery a "Higgs boson", preferring to call it the discovery of a "new boson".
That's because they don't yet know its properties â€“ and so can't confirm how similar it is to the Higgs of the standard model. "It's the beginning of a long journey to investigate all the properties of this particle," says Heuer.
One property that needs to be investigated is the particle's spin: the standard model says it should have a value of zero; a more exotic boson would give a value of two. Oliver Buchmueller of CMS says the LHC should be able to determine the new boson's spin by the end of 2012.
We know that the standard model is not complete â€“ it does not contain dark matter or gravity, for a start â€“ so a non-standard model Higgs could be very exciting.
"Everyone is not just excited about the discovery, but about the prospects this discovery offers to the field," says Heuer.ReferencesPaul Rincon Higgs boson-like particle discovery claimed at LHC
, BBC News Science and Environment, 4 July 2012. Link: http://www.bbc.co.uk/news/world-18702455
.Gordon Kane The Mysteries of Mass
, Published in The Frontiers of Physics
, Scientific American Special Edition, 2005