A simulation of a particle collision inside the Large Hadron Collider, the world's largest particle accelerator near Geneva. When two protons collide inside the machine, they create an energetic explosion that gives rise to new and exotic particles.
updated 6/17/2011 7:15:57 PM ET 2011-06-17T23:15:57

We'll have to take physicists' word for it that "one inverse femtobarn" is a lot. That's the milestone recently reached by the world's largest atom smasher, the Large Hadron Collider.

Inside the circular machine, which is buried 574 feet underground near Geneva, Switzerland, scientists accelerate protons to speeds approaching that of light, and then crash them into each other to produce energetic wrecks that can give rise to new and exotic particles.

The Large Hadron Collider (LHC) at the CERN physics lab began operating in 2008, and has been ramping up its power levels and the intensity of its particle beams. On Friday at 4:50 a.m. ET, the amount of data accumulated by two LHC experiments called ATLAS and CMS clicked over from 0.999 to 1 inverse femtobarn.

A "barn" is a unit of area, about equal to the cross-sectional area of the nucleus of a uranium atom. The prefix "femto" means 10−15 or 0.000000000000001, and an inverse femtobarn is a measurement of particle collisions per area — in other words, how many atoms actually smash together inside the machine.

The more particle collisions that LHC creates, the better its chances of discovering new physics.

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"This is a superb achievement, which demonstrates the outstanding performance of the accelerator and of the operation team," Fabiola Gianotti, spokeswoman for the ATLAS experiment, said in a statement. "The ATLAS physicists, in particular students and postdocs, are working hard and with great enthusiasm to produce exciting results, from precise measurements of the known particles to searches for the Higgs boson and other new phenomena. It's really a gorgeous moment!"

The Higgs boson is one of the atom smasher's most prized targets. Physicists think this theoretical particle, also dubbed the God particle, might be responsible for giving other particles mass. Though the Higgs has long been predicted to exist, it has never been seen. Many researchers are holding out hope that LHC will finally be powerful enough to create it.

"With the LHC running at much higher intensity than initially foreseen, signals of new physics might appear any moment in our data," said CMS spokesman Guido Tonelli. "Hundreds of young researchers all over the world are actively searching for new particles such as the Higgs boson, supersymmetric particles or new exotic states of matter. If nature is kind to us, we could have major breakthroughs even before the end of this incredibly exciting year."

You can follow LiveScience senior writer Clara Moskowitz on Twitter @ClaraMoskowitz. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

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Interactive: Inside the big bang machine

Explainer: What’s a hadron? Tour the particle zoo

  • Image: Elementary particles

    The Standard Model of particle physics is one of science's most successful theories, enabling the development of devices ranging from light bulbs, to microwave ovens and television, to quantum computing devices. The Standard Model is also one of the oddest theories, because it lays out a dizzying menagerie of hundreds of subatomic particles. At its heart are 16 types of elementary particles ... plus at least one more mysterious particle that scientists are spending billions of dollars to detect.

    Click on "Next" to get the full rundown.

  • Quarks

    Image: Quarks and gluons
    Berkeley Lab

    Six "flavors" of quarks have been detected: up and down, charm and strange, top and bottom. Quarks are almost always found in different combinations, bound together by gluons (more on those later). Particles built up from quarks and gluons are called hadrons. The Large Hadron Collider is so named because it's a large collider that smashes hadrons together.

    Three-quark combinations fit in the category of baryons. The best-known baryons are the proton (with two up quarks and one down quark) and the neutron (with two down quarks and one up quark).

    Particles that have one quark and one antiquark fit in the category of mesons. For example, the pion, or pi meson, contains an up quark and an anti-down quark.

  • Leptons

    Image: Single electrons in helium
    Brown University

    Six "flavors" of leptons have been detected: The negatively charged electron is the best-known lepton — along with its antimatter counterpart, the positron. This photo shows the path of single electrons passing through liquid helium, in an experiment devised by Brown University researchers.

    The muon is also negatively charged, but it's about 207 times as massive as the electron. ("Who ordered that?" physicist Isidor Rabi reportedly asked.) The negatively charged tau particle is even bigger — 3,477 times as massive as the electron — but it decays into other particles in less than a trillionth of a second.

    Each of those leptons has a neutrino associated with it: the electron neutrino, the muon neutrino and the tau neutrino. Neutrinos interact only weakly with other particles, and they zip through our planet virtually without a trace. Physicists only recently determined that they have mass, but there's still a great deal of mystery surrounding the ghostly particles.

  • Force carriers

    Image: Graviton

    The Standard Model sets aside a category for particles that are associated with force fields. The effect of a field can be viewed as involving an exchange of such force-carrying particles.

    Four elementary force-carrying particles have been detected. The best-known force carrier is the photon — which plays a part in the electromagnetic spectrum, including visible light. The gluon binds quarks together through the strong nuclear force. The weak nuclear force involves the exchange of W and Z bosons. The W boson can carry a positive or a negative charge, while the Z boson is neutral.

    If gravity could be incorporated into the Standard Model, the force-carrying particle would be called the graviton (shown here in an artist's depiction). However, gravitons have not yet been detected, and at least for now, such particles are not accounted for in the Standard Model.

  • Bosons vs. fermions

    Image: Bosons vs. fermions
    Rice Univ. via AIP

    All force-carrying particles are bosons, but not all bosons are force carriers. The difference has to do with a property known as particle spin. Particles with a fractional spin value (for example, electrons, protons and neutrons) are fermions. Two identical fermions cannot occupy the same quantum state. This is a property that keeps electrons from collapsing into a jumble, and thus makes chemical reactions possible.

    All particles with a whole-integer spin value are classified as bosons, and such particles can occupy the same quantum state even if they're identical. The photon is the best-known type of boson.

    Even atoms can be classified as fermions and bosons. This photo shows how atom clouds of lithium-7 (bosons) and lithium-6 (fermions) behave at low temperatures. The bosons collapse into a compact cloud, while the fermions can't squeeze that closely together.

  • The mysterious Higgs

    Image: Higgs as seen by CMS
    Ianna Osborne / CERN / CMS Collection

    The Higgs boson is the only particle predicted by the Standard Model that has not yet been detected. The Higgs is the main quarry for physicists at the Large Hadron Collider. This image is a simulation of the Higgs' signature as it might appear in one of the LHC's detectors.

    The Higgs boson, named after Scottish theorist Peter Higgs, is thought to be associated with a field that endows some particles (such as the weak nuclear force's W and Z bosons) with mass, while leaving the electromagnetic force's photons without mass.

    This Higgs field may have played a role at the very beginnings of the universe: Physicists believe that at the highest energies, the electromagnetic and weak nuclear forces were unified, but something led to "electroweak symmetry breaking" as the infant cosmos cooled. That would be why the electromagnetic force and the weak nuclear force are distinct in the current universe. The Large Hadron Collider could shed new light on this mysterious Higgs mechanism.

  • Why so complicated?

    Image: Particle zoo
    Tim Jones / McDonald Observatory / HETDEX

    Hadrons and leptons? Baryons and mesons? Fermions and bosons? Sometimes it seems as if particle physicists set up these classifications just to keep outsiders totally confused. But for researchers, these occasionally overlapping categories are useful for figuring out how different types of particles interact with each other.

    In a sense, it's as if we've been talking about the game of chess but have gotten only to the point of naming the different pieces on the board: black pieces and white ones, pawns and knights, bishops and rooks, kings and queens. The real meaning of the game comes out when you start studying how the pieces perform and interact.

    To delve into the deeper meaning of the Standard Model, you can visit The Particle Adventure at Lawrence Berkeley National Laboratory, "A Subatomic Venture" at CERN, or Particle Physics UK.

Photos: How the biggest collider was built

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  1. Heart of the machine

    A worker stands inside the ATLAS detector, surrounded by its eight toroidal magnets, just before the installation of the machine's calorimeter. ATLAS, the largest particle detector at Europe's Large Hadron Collider, sits inside an underground cavern as big as a cathedral. (Maximilien Brice / CERN) Back to slideshow navigation
  2. Mission control

    Members of the ATLAS detector team monitor operations at their control room on the campus of Europe's CERN particle-physics research center. A cutaway view of the particle detector can be seen on the computer screen at far right. (Claudia Marcelloni / CERN) Back to slideshow navigation
  3. Down the hole

    The last of 1,746 superconducting magnets is lowered into the Large Hadron Collider's beamline tunnel via a specially constructed pit in April 2007, as seen in this fish-eye view. Dipole magnets like this one produce a magnetic field that is 100,000 times stronger than Earth's, to bend beams of subatomic particles around the circular accelerator. (Claudia Marcelloni / CERN) Back to slideshow navigation
  4. Making the connection

    A welder works on the interconnection between two of the Large Hadron Collider's superconducting magnet systems in the collider tunnel. (Maximilien Brice  / CERN) Back to slideshow navigation
  5. Wheel of fortune

    One of the wheel-shaped slices of the ATLAS muon detector is lowered into a cavern for assembly into a giant device designed to look for evidence of exotic subatomic particles such as the Higgs boson. The Higgs particle is thought to play a key role in producing the property of mass in the universe. (Claudia Marcelloni & J. Pequenao / CERN) Back to slideshow navigation
  6. The theorist and the experiment

    World-famous theoretical physicist Stephen Hawking takes a look at the Large Hadron Collider's underground beamline during a visit in September 2006. (CERN) Back to slideshow navigation
  7. Pulling the trigger

    Each experiment at the Large Hadron Collider requires a "trigger," a combination of hardware and software that decides which collisions are significant enough to pass along for further analysis. This is a fish-eye view inside the trigger chambers for the ALICE detector's muon spectrometer. (Aurelien Muller / CERN) Back to slideshow navigation
  8. Inside the big bang

    A technician from the ALICE installation team works on gas pipes for the detector. ALICE is designed to study lead-ion collisions so intense that they re-create the conditions that existed just after the big bang. (A. Saba & Mona Schweizer / CERN) Back to slideshow navigation
  9. Cycles within cycles

    Technicians often use bicycles to get around the Large Hadron Collider's 17-mile-round tunnel. (Maximilien Brice / CERN) Back to slideshow navigation
  10. Dwarfed by science

    The LHCb detector is designed to study why matter dominates over antimatter in the universe. The worker peeking out from the concrete barriers at left is dwarfed by the detector's lip-shaped magnet assembly at right. (CERN) Back to slideshow navigation
  11. The PC farm

    CERN's Computer Center stores the quadrillions of bytes of data generated by experiments at the Large Hadron Collider and distribute the information to thousands of researchers around the world, using a network known as the LHC Computing Grid. (Maximilien Brice / CERN) Back to slideshow navigation
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