On November 30, 2009, the scientists at CERN were finally able to restart the experiments at the Large Hadron Collider (LHC) after a hiatus of more than a year. These experiments, which started slowly and gently because of complications last year with some faulty construction, will hopefully help us understand the origins of the universe, what the base particles of matter are, and how those particles are held together.

Restarting the LHC

When the LHC was restarted, it started with relatively low intensity beams and did not make those beams collide to ensure the integrity of the collider and its systems. Then, the scientists collided those beams to ensure that the energy was able to be handled and controlled and that the collection of data was working well. Up until that point, each beam only contained one proton bunch, but by December 4, 2009, the scientists began circulating multiple bunches.

The next step was to increase the energy in the beams. The LHC operators tested 450 GeV (gigaelectronvolts) before progressing to 1.18 TeV (teraelectronvolts). During all of these tests, the cryo-experts (technicians handling the temperature) and vacuum experts have intervened to adjust parameters in order to make the LHC work at peak performance and avoid another year-long shutdown.

How does the LHC work?

The LHC works by causing two beams of hadrons, composed of either protons or lead ions, to collide at 99.99% of the speed of light. These beams can gain energy up to 7 TeV, which will cause a collision of up to 14 TeV. To avoid collision with stray air molecules in the collector, the accelerator has been rendered a vacuum more sparse than the solar system, one comparable to that in interplanetary space. Also, in order to handle the high temperatures generated by these collisions, the accelerator is cooled to approximately -271.3°C, which is colder than outer space.

Six experiments

The LHC is composed of six unique experiments (ALICE, ATLAS, CMS, LHCb, TOTEM, and LHCf), which span a ring over a 26km circumference.

  • ALICE (A Large Ion Collider Experiment) studies quark-gluon plasma, a state of matter that scientists believe existed right after the Big Bang. By colliding the beams, scientists hope to generate enough energy to “melt” the protons and neutrons in the beams and creating the plasma.
  • The next two experiments are general purpose detectors. Their jobs include searching for the Higgs boson, extra dimensions, and particles of dark matter. ATLAS and CMS (Compact Muon Solenoid) use magnetic detectors to find these particles; however, the two experiments use vastly different technical solutions and designs to obtain their goals.
  • The LHCb (Large Hadron Collider beauty) is focused on discovering why our universe is composed almost entirely of matter and hardly any antimatter. This is accomplished by studying a particle called the “beauty quark” or “b quark.”
  • TOTEM (TOTal Elastic and diffractive cross section Measurement) is designed to measure the size of the proton and measure the LHC’s luminosity. TOTEM will also complement CMS’ data and help support the other LHC experiments.
  • LHCf ( Large Hadron Collider forward) simulates cosmic rays using the LHC’s own particle emissions. This will help scientists learn how cosmic rays’ interaction with Earth’s upper atmosphere leads to the particles that reach ground level.

Check out the TechRepublic gallery of LHC images.

A holiday break

The LHC is shut down for the holiday season. When they restart in 2010, the first thing tested will be to increase the intensity and energy to 3.5 TeV per beam. This level of energy marks the minimum necessary for the six experiment sites to achieve their full spectrum of tests.

Related resource: Read Crave’s recent interview with LHC scientist Dr. Paul Jackson.