When scientists at the European Organization for Nuclear Research (CERN) successfully collided twin proton beams at 7 TeV this week, it set a major milestone for the world's biggest and most expensive machine, the Large Hadron Collider (LHC), and marked the official start of the LHC research program. Now, particle physicists around the world are looking forward to a potentially rich harvest of new physics as the LHC begins its first long run at energy three and a half times higher than previously achieved at a particle accelerator.
After an early technical glitch threatened to delay the event, CERN scientists successfully collided two beams at 7 TeV for the first time in history. "It's a great day to be a particle physicist," said CERN Director General Rolf Heuer. "A lot of people have waited a long time for this moment, but their patience and dedication is starting to pay dividends."
CERN will run the LHC for 18 to 24 months with the objective of delivering enough data to the experiments to make significant advances across a wide range of physics channels. As soon as they have "rediscovered" the known Standard Model particles, a necessary precursor to looking for new physics, the LHC experiments will start the systematic search for the Higgs boson.
With the amount of data expected, called one inverse femtobarn by physicists, the combined analysis of ATLAS (A Toroidal LHC ApparatuS), one of the six particle detector experiments constructed at the LHC, and Compact Muon Solenoid (CMS) will be able to explore a wide mass range. CERN scientists said there's even a chance of discovery if the Higgs boson, a hypothetical elementary particle arising from the Higgs mechanism, has a mass near 160 GeV. If it's much lighter or very heavy, it will be harder to find in the first LHC run, the organization explained.
"We've all been impressed with the way the LHC has performed so far," said Guido Tonelli, spokesperson of the CMS experiment, "and it's particularly gratifying to see how well our particle detectors are working while our physics teams worldwide are already analyzing data. We'll address soon some of the major puzzles of modern physics like the origin of mass, the grand unification of forces and the presence of abundant dark matter in the universe. I expect very exciting times in front of us."
For supersymmetry, ATLAS and CMS will each have enough data to double today's sensitivity to certain new discoveries. Even at the more exotic end of the LHC's potential discovery spectrum, this LHC run will extend the current reach by a factor of two. LHC experiments will be sensitive to new massive particles indicating the presence of extra dimensions up to masses of 2 TeV, where today's reach is around 1 TeV. Following this run, the LHC will shut down for routine maintenance, and to complete the repairs and consolidation work needed to reach the LHC's design energy of 14 TeV.
"Two years of continuous running is a tall order both for the LHC operators and the experiments, but it will be well worth the effort," said Heuer. "By starting with a long run and concentrating preparations for 14 TeV collisions into a single shutdown, we're increasing the overall running time over the next three years, making up for lost time and giving the experiments the chance to make their mark."
Being a cryogenic machine operating at very low temperature, the LHC takes about a month to bring up to room temperature and another month to cool down. The organization said a four-month shutdown as part of an annual cycle no longer makes sense for such a machine, so CERN has decided to move to a longer cycle with longer periods of operation accompanied by longer shutdown periods when needed. Traditionally, CERN has operated its accelerators on an annual cycle, running for seven to eight months with a four- to five-month shutdown each year.