CERN physicists find hint of Higgs boson

^{Genesis 1.1-5: The First Day}

¹In the beginning, God created the heavens and the earth. ²The earth was without form and void, and darkness was over the face of the deep. And the Spirit of God was hovering over the face of the waters.

³And God said, "Let there be light," and there was light. ⁴And God saw that the light was good. And God separated the light from the darkness. ⁵God called the light Day, and the darkness he called Night. And there was evening and there was morning, the first day.

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http://www.latimes.com/news/science/la-sci-higgs-boson-20111214,0,7076752.story

By Eryn Brown, Los Angeles Times

December 14, 2011

 

Physicists find 'tantalizing hints' of Higgs boson 'God particle'



Higgs candidate event from the ATLAS experiment. A proton-proton collision in the ATLAS detector, the bright green rods illustrate two detected photons produced in the high energy collision. These could be the result of a Higgs boson being produced and decaying into two photons.

Two teams of scientists at the Large Hadron Collider near Geneva say they detected 'tantalizing hints' of the elusive Higgs boson, or 'God particle,' but no definitive proof.

Physicists announced Tuesday that they had detected "tantalizing hints," but not definitive proof, of the long-sought Higgs boson, the so-called God particle that is crucial to physicists' understanding of why mass exists in the universe.

Two large teams of scientists based at the Large Hadron Collider near Geneva separately saw what they believe are telltale tracks of the maddeningly elusive particle in the aftermath of about 400 trillion proton collisions carried out since January.

Neither group had solid enough evidence to announce an official discovery, they reported. But the fact that both teams generated similar results — and that those results were in good alignment with the predictions of theoretical physicists — indicated that scientists may be closing in on the Higgs at last.

"It's looking very good," said UC Davis theoretical physicist John Gunion, who was not involved in the experiments but has been following them closely. "What's really important is that both teams see the same thing."

The results were presented Tuesday afternoon in a packed auditorium at the Large Hadron Collider, which is operated by CERN, the European Organization for Nuclear Research.

The collider sends beams of protons hurtling toward each other at nearly the speed of light. Two massive detectors, known as ATLAS and CMS, analyze the subatomic particles released by the collisions. Certain patterns are thought to indicate that a collision has produced a Higgs boson.

Both teams reported possible Higgs sightings that suggested the particle has a relatively light mass, somewhere around 125 billion electron volts.

But the margins of error for those sightings were still considerable: The ATLAS team said its calculations came with a statistical significance of about 2.3 sigma and the CMS team said its was about 1.9 sigma.

Once the teams' results are carefully combined, the significance could rise above 3 sigma, Caltech physicist Sean Carroll said. Physicists require a significance of at least 3 sigma before considering a finding "evidence," and they need to reach the 5-sigma threshold to declare they've made a "discovery."

Data from additional experiments will allow both teams to narrow their margins of error and determine whether the Higgs signal is real, said Fabiola Gianotti, a physicist on the ATLAS team.

"By the end of 2012 — sooner, if we are lucky — we should be able to have the final word," Gianotti told those gathered at CERN.

In a post on the Cosmic Variance blog, Carroll compared the news to "rushing to the tree on Christmas morning, ripping open a giant box, and finding a small note that says 'Santa is on his way! Hang in there!'"

The CERN results have been eagerly anticipated by physicists hoping to find experimental support for the Standard Model of particle physics, the theory that explains how subatomic particles interact to make up the building blocks of the universe.

But an important piece of evidence supporting the Standard Model never materialized: the Higgs boson. It is the particle associated with the so-called Higgs field, an energy field that gives mass to particles through a process known as the Higgs mechanism. (All are named for University of Edinburgh physicist Peter Higgs, one of several scientists who proposed the idea during the 1960s.)

If the theory is correct, scientists should be able to detect the Higgs boson, or multiple Higgs bosons, by smashing subatomic particles together at high energies, simulating conditions in the early universe.

Older particle accelerators, including the Tevatron at Fermilab in Batavia, Ill., were able to narrow the range of possible masses for the Higgs, but they weren't powerful enough to find the particle. The search was one of the primary reasons for building the $5-billion Large Hadron Collider.

Whether additional data prove or rule out the existence of the Higgs boson next year, scientists said, there are many years of physics research left to conduct at the collider.

If the particle is there, researchers will investigate its properties. If the particle isn't there, "then something else has to show up in our experiments," said Markus Klute, an MIT physicist who works with the CMS team.

Either way, he said, "we start a new chapter in Higgs physics."

eryn.brown@latimes.com

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http://news.cnet.com/8301-30685_3-57342044-264/cern-physicists-find-hint-of-higgs-boson/

by Stephen Shankland

December 13, 2011 6:33 AM PST

These red lines show how the LHC's Atlas experiment registered the arrival of four particles called muons. They could have been the byproducts of a short-lived Higgs boson--or they could have been more humdrum events. CERN's LHC particle accelerator will continue smashing protons into each other to spot the statistical significance that means the Higgs really has been found. (Credit: CERN)

Researchers at the CERN particle accelerator have found "intriguing hints" of the Higgs boson, a moment of major progress in years of previously unfruitful searching for the elusive subatomic particle.

The search for the Higgs boson is the top priority of CERN's massive and expensive Large Hadron Collider near Geneva, Switzerland. Its Atlas experiment showed a statistically suspicious increase in activity that indicates the Higgs could be pinned down with a mass of 126 giga-electron-volts, and showing some important agreement, its independent CMS experiment found a possible result nearby at 124GeV.

"We observe an excess of events around mass of about 126 GeV," CERN physicist and Atlas leader Fabiola Gianotti said in slides presented today at a CERN seminar to physicists who applauded her results. That equates to about 212 quintillionths of a gram; by comparison, a proton is more than 100 times lighter with a mass of 0.938GeV.

Her small sentence carries big import for physics. That's because the Higgs boson, thought by some to endow other particles with mass, is a key missing ingredient in physicists' understanding of what makes the universe tick. It's predicted by the Standard Model of particle physics, but no one has been able to confirm its existence or nature.

"The Higgs could be the first link in a chain of discovery. This is what we hope," said Guido Tonelli of the Universita degli Studi di Pisa and leader of the CMS project, in a news conference after the seminar. Another year of continued data gathering should be enough to provide a conclusive answer on this particular matter, the physicists said.

Gianotti called the findings "beautiful results" at the seminar, but stopped well short of declaring victory because there's not enough data for statistical certainty. "It's too early to draw definite conclusions...We believe we have built a solid foundation on the exciting months to come."

Finding the Higgs boson is essentially a matter of checking for a variety of events--or their absence. The LHC's detectors have been gradually ruling out ranges of possible mass for the Higgs boson.

"The window for the Higgs mass gets smaller and smaller," and today we saw "intriguing hints" of its possible nature, said CERN Director General Rolf Heuer. "We have not found it yet. We have not excluded it yet. Stay tuned for next year."

Inside the Large Hadron Collider (photos)

The Higgs boson isn't observed directly, but rather is detected by extremely rare side effects of collisions between protons smashing into each other. To increase the likelihood of collisions, the LHC operators have been gradually increasing the beam intensity.

CERN physicist Fabiola Gianotto describes scientific results

from the Large Hadron Collider's search for the Higgs boson.

(Credit: Screenshot by Stephen Shankland/CNET)

Gianotti also said the CMS results predict with a 95 percent confidence level that the Higgs boson has a mass between 115.5GeV and 131GeV.

Another experiment, the Compact Muon Solenoid (CMS), also helped narrow down the possible mass of the Higgs boson. Its results showed with a 95 percent confidence level that the particle can't be between 127GeV and 600GeV, Tonelli said.

The CMS experiment also found "a modest excess of events" that could be evidence of the Higgs boson between 115GeV and 127GeV, Tonelli said in a presentation at the seminar. "The excess is most compatible with a Standard Model Higgs hypothesis in the vicinity of 124GeV and below, but the statistical significance is not large enough to say anything conclusive."

One of the big mysteries that physicists hope to plumb with the Higgs is an idea called supersymmetry. The Standard Model predicts a wide range of particles, of which the Higgs is the last to be pinned down. But with supersymmetry, each of the conventional elementary particles in the standard model, including the Higgs, has a companion. If there's only one Higgs boson, it's part of the Standard Model. But with supersymmetry, there have to be at least five Higgs bosons. Supersymmetry would double the number of particles to resolve physics problems in a similar way that the prediction--and later discovery--of antimatter did decades ago.

If the Higgs boson weighs about 125GeV, it would match many physicists' general expectations--but also carry some importance. That's because it's at the light end of the range of possibilities, and physicists believe a particle that light needs another particle from the sypersymmetry collection to anchor it.

"Our expectation is that you have something heavy. It could be something related to SUSY," Tonelli said, referring to the nickname for supersymmetry theory. "Or maybe not," he added.

The CMS, or Compact Muon Solenoid, is not what most people would call compact. It's one of the two general-purpose experiments at the Large Hadron Collider with which physicists hope to detect the Higgs boson. (Credit: Maximilien Brice/CERN)

When it comes to mass, physicists liken the Higgs boson to groupies at a party. Heavy particles interact strongly with Higgs bosons, equivalent to a lot of people swarming a celebrity and making it harder for the famous person to start moving and, once moving, harder to stop. Particles with little mass are those that interact weakly with Higgs bosons, making them more fleet-footed.

"A heavier particle is nothing more that one than has more interactions with the Higgs particle as it passes through the vacuum," said Lawrence Sulak, chairman of Boston University's physics department.

If the Higgs boson is precisely measured in the next year, the LHC can be used to look further down the same pathway, Tonelli added, possibly finding supersymmetric particles--"if they are in the energy range of the LHC."

Such particles would likely be vastly heavier--many thousands, perhaps millions, of GeVs, he said.

That would be quite a coup: supersymmetric particles are a possible explanation for dark matter, material that in the universe outweighs the ordinary matter of which we're made but that generally interacts with ordinary matter only through gravitational pull.

To find harder particles, CERN plans an LHC upgrade that will let protons be smashed together at twice today's energy level. "Hopefully we'll explore a large region of masses," Tonelli said. And then, the supersymmetry work can begin in earnest. "A lot of parameters are still open, a lot of SUSY models are still open and are waiting to be excluded or confirmed," he said.

The LHC is a huge, phenomenally complex instrument built in a circular subterranean tunnel 27 kilometers in circumference. It can accelerate protons fast enough that, when they collide, they reproduce energy levels found only in the earliest moments of the universe after the Big Bang.

Updated at 7:26 a.m. PT and 10:44 a.m. PTwith further detail.

Fabiola Gianotti's conclusions about the LHC's Atlas experiment results about the search for the Higgs boson

(Credit: Screenshot by Stephen Shankland/CNET)

Guido Tonelli's conclusions about the LHC's CMS experiment results about the search for the Higgs boson.

(Credit: Screenshot by Stephen Shankland/CNET)