By Denise Overbye, The New York Times, July 4, 2012
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| British physicist Peter Higgs arrived at CERN headquarters today |
ASPEN, Colo. —
Physicists working at CERN’s Large Hadron Collider said Wednesday that they
had discovered a new subatomic particle that looks for all the world like the Higgs boson, a potential key to an
understanding of why elementary particles have mass and indeed to the existence
of diversity and life in the universe.
The
British physicist Peter Higgs arrived at CERN's headquarters on Wednesday.
“I think we have it,” Rolf-Dieter Heuer, the director general of CERN,
said in an interview from his office outside Geneva, calling the discovery “a
historic milestone.” His words signaled what is probably the beginning of the
end for one of the longest, most expensive searches in the history of science.
If scientists are lucky, the discovery could lead to a new understanding of how
the universe began.
Dr. Heuer and others said that it was too soon to know for sure
whether the new particle, which weighs in at 125 billion electron volts, one of
the heaviest subatomic particles yet, fits the simplest description given by
the Standard Model, the theory that has ruled physics for the last
half-century, or whether it is an impostor, a single particle or even the first
of many particles yet to be discovered. The latter possibilities are
particularly exciting to physicists since they could point the way to new
deeper ideas, beyond the Standard Model, about the nature of reality. For now,
some physicists are calling it a “Higgslike” particle.
“It’s great to discover a new particle, but you have find out what its
properties are,” said John Ellis, a theorist at CERN, the European Organization
for Nuclear Research.
Joe Incandela, of the University of California, Santa Barbara, a
spokesman for one of two groups reporting data on Wednesday, called the
discovery “very, very significant.”
“It’s something that may, in the end, be one of the biggest
observations of any new phenomena in our field in the last 30 or 40 years,
going way back to the discovery of quarks, for example,” he said.
Here at the Aspen Center for Physics, a retreat for scientists that
will celebrate its 50th birthday on Saturday, the sounds of cheers and popping
corks reverberated early Wednesday against the Sawatch Range through the
Roaring Fork Valley of the Rockies, as bleary-eyed physicists watched their
colleagues read off the results in a webcast from CERN. It was a scene
duplicated in Melbourne, Australia, where physicists had gathered for a major
conference, as well as in Los Angeles, Chicago, Princeton, New York, London and
beyond — everywhere that members of a curious species have dedicated their
lives and fortunes to the search for their origins in a dark universe.
Nima Arkani-Hamed, a physicist at the Institute for Advanced Study in
Princeton, said: “I was really impressed. It’s a triumphant day for fundamental
physics. Now some fun begins!”
At CERN itself, 1,000 people stood in line all night to get into the
auditorium, according to Guido Tonelli, a CERN physicist who said the
atmosphere was like a rock concert. Peter Higgs, the University of Edinburgh
theorist for whom the boson is named, entered the meeting to a standing
ovation.
Confirmation of the Higgs boson or something very much like it would
constitute a rendezvous with destiny for a generation of physicists who have
believed in the boson for half a century without ever seeing it. And it affirms
a grand view of a universe ruled by simple and elegant and symmetrical laws,
but in which everything interesting in it, like ourselves, is a result of flaws
or breaks in that symmetry.
According to the Standard Model, which has ruled physics for 40 years,
the Higgs boson is the only visible and particular manifestation of an
invisible force field, a cosmic molasses that permeates space and imbues
elementary particles that would otherwise be massless with mass. Particles
wading through it would gain heft.
Without this Higgs field, as it is known, or something like it,
physicists say all the elementary forms of matter would zoom around at the
speed of light, flowing through our hands like moonlight. There would be
neither atoms nor life.
Physicists
said that they would probably be studying the new Higgs particle for years. Any
deviations from the simplest version of the boson — and there are hints of some
already — could open a gateway to new phenomena and deeper theories that answer
questions left hanging by the Standard Model: What, for example, is the dark matter that provides the gravitational
scaffolding of galaxies? And why is the universe made of matter instead of
antimatter?
“If the boson
really is not acting standard, then that will imply that there is more to the
story — more particles, maybe more forces around the corner,” Neal Weiner, a
theorist at New York University, wrote in an e-mail. “What that would be is
anyone’s guess at the moment.”
One intriguing candidate for the next theory they have been on the
watch for is called supersymmetry, “SUSY” for short, which would come with a
whole new laundry list of particles to be discovered, one of which might be the
source of dark matter. In supersymmetry there are at least two Higgs bosons.
Dr. Incandela said, “The whole world thinks there is one Higgs, but
there could be many of them.”
Michael Turner, a cosmologist at the University of Chicago and the
chairman of the physics center board, said, “This is a big moment for particle
physics and a crossroads — will this be the high water mark or will it be the
first of many discoveries that point us toward solving the really big questions
that we have posed?”
Wednesday’s announcement is also an impressive opening act for the
Large Hadron Collider, the world’s biggest physics machine, which collides
protons and only began operating two years ago. It is still running at only
half-power.
Physicists had been holding their breath and perhaps icing the Champagne
ever since last December. Two teams of about 3,000 physicists each — one named
Atlas, led by Fabiola Gianotti, and the other CMS, led by Dr. Incandela —
operate giant detectors in the collider, sorting the debris from the primordial
fireballs left after proton collisions. Last winter they both reported hints of
the same particle. They were not able, however, to rule out the possibility
that it was a statistical fluke.
Since then the collider has more than doubled the number of collisions
it has recorded.
The new results capped three weeks of feverish speculation and
Internet buzz as the physicists, who had been sworn to secrecy, did a breakneck
analysis of some 800 trillion proton-proton collisions over the last two years.
They were racing to get ready for a major conference in Melbourne that started
on Wednesday, where they had promised an update on the Higgs search.
In the end, the CERN council, which consists of representatives from
each of CERN’s 20 member states, decided that the potentially historic
announcement should come from the lab’s own turf first.
Up until last weekend, physicists from inside were reporting that they
themselves did not know what the outcome would be, though many were having fun
with the speculation.
“HiggsRumors” became one of the most popular hashtags on Twitter. The
particle also acquired its own iPhone app, a game called “Agent Higgs.”
Expectations soared when it was learned that the five surviving originators of
the Higgs boson theory had been invited to the CERN news conference.
On the eve of the announcement, in what was an embarrassing moment for
the lab where the Web was invented, a video of Dr. Incandela making his
statement was posted to the Internet and then quickly withdrawn. Dr. Incandela
said he had made a series of video presentations with alternate conclusions so
that the video producers would not know the right answer ahead of time, but the
one that was right just happened to get posted.
But the December signal was no fluke.
Like Omar Sharif materializing out of a distant blur of heated air
into a man on a camel in “Lawrence of Arabia,” what was once a hint of a signal
had grown over the last year, until it practically jumped off the chart. “I
believe it now; I didn’t before,” said a physicist who was one of the first to
see the new results but was not authorized to discuss them.
The new particle has a mass of about 125.3 billion electron volts, in
the units of mass and energy — Einstein showed they are the same — that are
favored by physicists, about as much as a whole barium atom, according to the
CMS group, and 126 billion according to Atlas.
Both groups said
that the likelihood that their signal was a result of a chance fluctuation was
less than one chance in 3.5 million, so-called “five sigma,” which is the gold
standard in physics for a discovery.
On that basis, Dr. Heuer said that he had decided only Tuesday
afternoon to call the Higgs result a “discovery.”
He said, “I know the science, and as director general I can stick out
my neck.”
Dr. Incandela’s and Dr. Gianotti’s presentations were repeatedly
interrupted by applause as they showed slide after slide of data bumps rising
like mountains from the sea.
Dr. Gianotti said at one point: “Why are you applauding? I’m not done
yet. This is just beginning. There is more to come.”
She noted that the mass of the putative Higgs made it easy to study
its many behaviors and channels. “So,” she said, “thanks, nature.”
Gerald Guralnik, one of the founders of the Higgs theory, said he was
glad to be at a physics meeting “where there is applause like a football game.”
Asked to comment after the announcements, Dr. Higgs seemed
overwhelmed, saying, “For me, its really an incredible thing that’s happened in
my lifetime.”
In quantum theory, which is the language of particle physicists,
elementary particles are divided into two rough categories: fermions, which are
bits of matter like electrons; and bosons, which are bits of energy and can
transmit forces, like the photon that transmits light.
Dr. Higgs of the University of Edinburgh, was one of six physicists,
working in three independent groups, who in 1964 invented the notion of the
cosmic molasses, or Higgs field. The others were Tom Kibble of Imperial
College, London, Carl Hagen of University of Rochester, Dr. Guralnik of Brown
University, and Francois Englert and the late Robert Brout, both of Université
Libre de Bruxelles.
One implication of their theory was that this cosmic molasses,
normally invisible and, of course, odorless, would produce its own quantum
particle if hit hard enough, by the right amount of energy. The particle would
be fragile and fall apart within a millionth of a second in a dozen different
ways depending upon its own mass.
Unfortunately, the theory did not say how much this particle should
weigh, which is what made it so hard to find. The pesky particle eluded
researchers at a succession of particle accelerators, including the Large
Electron Positron collider at CERN, which closed down in 2000, and the Tevatron
at the Fermi National Accelerator Laboratory, or Fermilab, in Batavia, Ill.,
which shut down last year.
Along the way the Higgs boson achieved a notoriety rare for abstract
physics. To the eternal dismay of his colleagues, Leon Lederman, the former
director of Fermilab, called it the “God particle,” in his book of the same
name, later quipping that he had wanted to call it “the Goddamn particle.”
Finding the missing boson was one of the main goals of Large Hadron
Collider.
Both Dr. Heuer and Dr. Gianotti said they had not expected the search
to succeed so quickly, a tribute they said, to the people who had built the
collider and the detectors and learned to run them efficiently. “It’s truly
amazing,” said Lisa Randall, a prominent Harvard theorist.
Dr. Heuer recently extended the current run of the collider an extra
three months, to the end of the year, during which the experimenters say they
expect to triple their data on the new particle, narrowing some its possible
identities.
The collider will then shut down for two years for major repairs. When
it starts up again, theories of both inner space and outer space could be up
for grabs.
Although they have never been seen, Higgs-like fields play an
important role in theories of the universe and in string theory. Under certain
conditions, according to the strange accounting of Einsteinian physics, they
can become suffused with energy that exerts an anti-gravitational force. Such
fields have been proposed as the source of an enormous burst of expansion,
known as inflation, early in the universe, and, possibly, as the secret of the dark energy that now seems to be speeding up
the expansion of the universe.
Knowing more about the new particle will help put those theories on
firmer ground, Dr. Turner of Chicago said.
So far the physicists admit, they know little. The CERN results are
mostly based on measurements of two or three of the dozen different ways, or
“channels,” by which a Higgs boson could be produced and then decay.
There are hints, but only hints so far, that some of the channels are
overproducing the Higgs while others might be underproducing, clues maybe that
there is more than the Standard Model at work.
“This could be the first in a ring of discoveries,” said Dr. Tonelli.
CERN will be examining the rest of the channels over the coming months
and years, and the idea that the Standard Model could be cracking is a prospect
that physicists find thrilling. Only time, and a few more trillions of proton
collisions, will tell.
In an e-mail, Maria Spiropulu, a professor at the California Institute
of Technology who works with the CMS team at CERN wrote about the Higgs, “I
personally do not want it to be standard model anything — I don’t want it to be
simple or symmetric or as predicted. I want us all to have been dealt a complex
hand that will send me (and all of us) in a (good) loop for a long time.”
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