SWITZERLAND: Physicists are more
than 99 percent sure that they've found a new elementary particle that is
likely the long-sought Higgs boson.
Evidence for the new particle was
reported today (July 4) by scientists from the world's largest atom smasher,
the Large Hadron Collider in Switzerland. Researchers reported they'd seen a
particle weighing roughly 125 times the mass of the proton, with a level of
certainty that all but seals the deal it's the Higgs boson.
The Higgs, nicknamed the "God
particle" (to the chagrin of many scientists, who prefer its official
name), is thought to hold the key to one of the mysteries of the universe: Why
do things have mass?
Its discovery represents a major
step forward in our understanding of why the universe exists as it does, with
matter clumping together to form galaxies, stars, planets and us, scientists
say. [Top 5 Implications of Finding the Higgs Boson]
To be absolutely sure they've made a
true new discovery, rather than simply seen a fluke, physicists wait for enough
data so that their statistics reach a level called 5 sigma, meaning that there
is only a one in 3.5 million chance the signal isn't real.
"We observe in our data clear
signs of a new particle, at the level of 5 sigma, in the mass region around 126
GeV," said Fabiola Gianotti, spokesperson of LHC's ATLAS experiment. (GeV
stands for gigaelecton volts, a unit of mass roughly equivalent to the weight
of a proton.) Gianotti presented the findings to loud applause from physicists
gathered at CERN (LHC's home facility) to hear the LHC's results.
The LHC's CMS experiment saw signs
of a new particle with a mass of 125.3 GeV at a certainty level of 4.9 sigma.
"As a layman I would now say, I
think we have it," CERN director general Rolf Heuer said during a
presentation at the Geneva, Switzerland lab reporting the results today.
"Do you agree?" he asked the gathered physicists, who responded with
loud applause.
The Higgs boson is the last
undiscovered piece of the puzzle predicted by the reigning theory of particle
physics, called the Standard Model. Yet the model does not predict what its
mass is, so physicists have to search through a wide territory to find it. The
researchers can't yet be absolutely sure that the new particle they've found
actually is the Higgs.
"The work now is to actually
measure its quantum identity (all its quantum properties)," Caltech
physicist Maria Spiropulu, who was in the audience at the LHC announcement,
told LiveScience in an email. "Then we can say if it THE minimal standard
model Higgs or a Higgs look-alike. We have been propelled to the future of
particle physics towards the understanding of the fundamental properties of our
universe in its entirety."
The LHC is the most powerful machine
on Earth, capable of smashing protons together to produce huge explosions of
energy that transform into new and exotic particles inside its17-mile (27
kilometer) underground loop. Yet the Higgs boson is so rare only one out of a
trillion of the collisions inside the accelerator are likely to produce it, and
even then, it decays almost immediately into other particles.
"This is not a needle in a
haystack — it's much worse than a needle in a haystack," said Joe Lykken,
a theoretical physicist at the Fermi National Accelerator Laboratory (Fermilab)
in Batavia, Ill.
Over the past few years, researchers
have been able to exclude certain possible masses for the Higgs, narrowing the
possible window for Higgs further and further. Just this week, Fermi scientists
announced that data from the largest U.S. particle accelerator, the Tevatron
(which shut down last year), show the Higgs, if it exists at all, must have a
mass between 115 and 135 GeV.
In December 2011, the LHC teams
announced their latest findings, which restricted the Higgs to a mass
between115 and 130 GeV, though with less certainty than the new Tevatron
results.
"This is a really special
time," said Fermilab physicist Dan Green, a member of LHC's CMS
experiment, said Monday (July 2). "I remember when the top [quark] was
discovered 20 years ago. This is one of the most exciting weeks I've had for a
very long time." [9 Unsolved Physics Mysteries]
Today's findings come from the two
general-purpose experiments at LHC, ATLAS and CMS. Both observed particle
collisions independently and analyzed their observations separately. In fact,
scientists from each team were not allowed to tell each other what they found
until today, for fear their results would bias the other experiment's
researchers toward looking for the same results.
So this Higgss is what some of them called God's boson..
ReplyDelete