Less than five years after it went live, the Large Hadron Collider has confirmed the existence of a Higgs boson, the particle which may explain how other particles get their mass.
The confirmation comes today (March 14), after a July 2012 announcement of the elementary particle's discovery. At the time, researchers strongly suspected they'd found a Higgs, but needed to collect more data. Since then, they've more than doubled the amount of data they have on the particle using the Large Hadron Collider (LHC), a 17-mille-long (27 kilometers) underground ring on the French-Swiss border where protons zing around at near the speed of light.
With a Higgs boson discovered, what more is there for this enormous and unusual piece of machinery to do? Lots, according to physicists.
For one thing, scientists are still working out whether the Higgs boson they've discovered fits the Standard Model of physics or if it better fits another theory. (So far, the Standard Model appears to be the winning candidate.)
And the hunt for the Higgs boson is just one of the ongoing projects at the particle accelerator. Other projects have such humble goals as explaining dark matter, revealing the symmetries of the universe and even looking for new dimensions of space, according to the U.S. Department of Energy and the National Science Foundation.
"It really is a machine that's capable of going to higher energies, maybe ultimately to a factor of seven times higher energy," said Peter Woit, a physicist at Columbia University. "Which means going to distances seven times smaller and basically looking for anything you can find."
Here are the major projects ongoing at the LHC:
ALICE (A Large Ion Collider Experiment @ CERN): By smashing particles together, scientists can recreate the first few milliseconds after the Big Bang, illuminating the early history of the universe. A detector 52 feet (16 meters) high and 85 feet (261 m) long enables scientists to study what's known as quark-gluon plasma. The researchers collide heavy ions, liberating their quarks and gluons (quarks are the constituent part of protons, which are held together by gluons). It takes a machine like the LHC to separate these atomic particles and study them individually.
ATLAS (A Toroidal LHC Apparatus): This is the experiment that observed a Higgs in July. But ATLAS's work isn't done. The LHC, and the ATLAS detector, are currently in shutdown mode, preparing for an energy increase. When LHC starts up again after 2013, the atom smasher will be able to fling protons at each other at 14 teraelectronvolts (TeV), double its previous 7 TeV.
ATLAS has a broad mission. It's a tool that can search for extra dimensions of space and supersymmetry, the idea that every known particle has a "superpartner particle," an important component of string theory. Supersymmetry would, in turn, help elucidate dark energy, which may exist in the vacuum of space and be responsible for the acceleration of the universe's expansion. ATLAS is also part of the search for dark matter, a mysterious form of matter that may make up more than 95 percent of the universe's total matter density, but which is virtually unknown. [Whoa! The Coolest Little Particles in Nature]
CMS (Compact Muon Solenoid): Like ATLAS, CMS is a jack-of-all trades. The detector is meant to explore the same questions about the origins of the universe and the fundamentals of matter.
LHCb (Large Hadron Collider beauty): The LHCb project studies how B mesons decay. Mesons are particles made of a quark and an antiquark bound together; a B meson contains a flavor of quark known as the "b-quark." Studying this decay helps scientists understand imbalances between antimatter and matter. During the Big Bang, matter and antimatter should have been created in equal amounts, leading physics theories suggest. Even so, the world is made up nearly entirely of matter, so the mystery remains: What happened to the antimatter?
The LHCb will also study the decay products of the Higgs boson particle.
LHCf (Large Hadron Collider forward): This project is just spacey. The LHCf is focused on the physics of cosmic rays, charged particles that flow through space. Ultra-high-energy cosmic rays remain a mystery to physicists, who hope to find out their origins with the help of the LHCf experiment, which is a joint collaboration with the Pierre Auger Observatory in Argentina and the Telescope Array in Utah.
TOTEM (Total Cross Section, Elastic Scattering and Diffraction Dissociation): The TOTEM detector is small by LHC standards, involving only about 100 scientists (projects such as ATLAS have thousands). The goal is to measure how particles scatter at small angles from proton-proton collisions in the LHC. Collisions studied by TOTEM include those where one proton or both protons survive the crash, enabling scientists to calculate the likelihood of a collision destroying both protons. Those numbers, in turn, tell researchers the probability of producing particular particles in a collision.
One thread connecting all experiments at the Large Hadron Collider is the hope that something new and unexpected will arise.
"There's certainly a long history in physics where you get the ability to look at things at much smaller and smaller scales, you see something you didn't expect," Woit told LiveScience. "They're hoping the LHC would find something that we hadn't thought of. And that hasn’t happened yet, and maybe it never will."
LiveScience's Tia Ghose contributed reporting to this story.
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