'God Particle' Found? Search for the Higgs Boson Narrows
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Physics has a well-deserved reputation for being horrendously
complicated, but sometimes it's the simplest questions that lead to
truly profound insights. When Einstein asked himself, "What would
happen if you could ride on a beam of light?" for example, the answer
led him to the Special Theory of Relativity.
For the past few decades, particle physicists have been wrestling with
another deceptively simple question: Why does anything have mass? You
might wonder "why not?" But according to modern physics, you can't get
away that easily. The existence of mass — the property of matter that
gives gravity something to pull on — needs explaining.
(Photos: The Large Hadron Particle Collider)
Now, say two independent teams of scientists who revealed their
results at a symposium in Switzerland Tuesday morning, there are
experimental signs of an elusive particle formally known as the Higgs
boson — and informally known as the "God particle." If the Higgs is
really there, the existence of mass has finally been explained, and a
Scottish physicist named Peter Higgs is a lock for the Nobel prize.
It's a big "if," though, and nobody is making an actual claim. Indeed,
said Fabiola Gianotti, a member of one of the teams said at the
symposium. "We cannot conclude anything at this stage."
(Top 10 Scientific Breakthroughs)
But that hardly means there's nothing to say. The gathering took place
in a packed auditorium at the CERN laboratory outside Geneva — the
home of the mammoth Large Hadron Collider. The LHC, which is the
world's most powerful particle accelerator, works by taking subatomic
protons, sending them racing in opposite directions through a 17-mile
oval-shaped tunnel, then letting them smash together head-on at nearly
the speed of light. The impact is powerful enough to vaporize the
particles into tiny fireballs of pure energy, recreating conditions in
the first moments after the Big Bang. Then, just as in the early
universe, the energy re-condenses into particles. Among them may be
the elusive Higgs.
That's what physicists have been hoping for, anyway, since long before
the LHC was even built. It was way back in the 1960's that Peter
Higgs, of the University of Edinburgh, proposed what came to be known
as the "Higgs mechanism" (others came up with similar ideas, but his
is the name that stuck). The way it works is ... no, let's not go
there. Suffice it to say that there's a sort of energy field that
pervades the universe, and that when particles like protons, neutrons,
quarks and the rest interact with the Higgs field, they're rewarded
with mass. The Higgs boson helps broker the transaction.
(Photos: Seeking Beauty in Scientific Research)
When the Higgs condenses out of particle collisions, it immediately
decays into other particles, so physicists can't see it directly; they
can only reconstruct its existence from the debris, like a CSI unit
reconstructing what a bomb must have looked like from the fragments.
And since each mini-Big Bang creates so many particles that decay into
so many other particles, the reconstruction is incredibly difficult.
The good news is that the new hints of a Higgs in all of that particle
debris come from not one, but two entirely different detectors at the
LHC — the ATLAS (for "A Toroidal LHC ApparatuS") and the CMS (for
Compact Muon Solenoid). The two operate in different ways, as a sort
of mutual cross-check.
Both detectors have seen evidence of the Higgs — which is big news and
the reason for both the symposium and all of the speculation that
attended its announcement. But the less good news is that in
statistical terms, that evidence weighs in at what is known as the
three-sigma confidence level. No need to go here in too much detail
either, except to say you'd need to get to the five-sigma stage to
claim an actual discovery. "It's too early to draw a definite
conclusion," said Gianotti. "We need four times as much data."
(See "Higgs Boson May Have Been Found! (But Probably Not.)")
Getting that data requires many thousands of fireballs, and the LHC
accelerator will need another year or more to crank all of them out
and allow Gianotti and her colleagues to announce that they've indeed
discovered the Higgs boson. Or not. "The number of sub-three-sigma
discoveries that have turned out to be wrong," says Princeton
astrophysicist Michael Strauss, "is reasonably large."
You'd think that if the hunt for the Higgs comes to nothing it would
be a big disappointment for physicists. But it's not necessarily so.
Finding the Higgs would add a key missing brick to the edifice of the
so-called Standard Model of particle physics, which would be important
— but also just a bit dull.
(See "Why the Large Hadron Collider Matters: The Search for the 'God
Particle'")
"The great irony," Harvard theorist Lisa Randall told the New York
Times a day or two ago, "is that not finding a Higgs boson would be
spectacular from the point of view of particle physics, pointing to
something more interesting than the simple Higgs model." For
physicists, it turns out, "be careful what you wish," especially if
you're wishing for a Higgs, may truer than it seems.
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