From the page: The LHC's eight sectors have all been cooled to 1.9 kelvin (-271 C, or -456 F) using cryogenic lines containing liquid helium. This operating temperature is colder than conditions in deep space, which is estimated to be 2.7 K. Zero K is the lowest temperature possible.
The magnets that bend particle beams around the LHC need to be this cold because at these low temperatures they become superconductors, channeling electric current with almost no power loss, and with zero resistance.
In the LHC experiments, two beams of protons will be fired in opposite directions through the ring between the magnets. They will reach close to the speed of light, and smash into one another at four collision points. The collisions are predicted to produce thousands of particles, which will be studied by the scientists, The results are expected to shed new light on the nature of the universe and its beginnings.