Just after 1 pm European time today, the LHC at CERN collided two beams of protons with a total center-of-mass energy of 7 TeV (seven trillion electron volts), three and a half times more energy than the proton-antiproton collisions at the Tevatron at Fermilab, and far greater than the 2.4 TeV achieved by the LHC in December 2009. This milestone clearly marks the beginning, at long last, of the first major physics run of the new accelerator.
We’ve been waiting a very long time for this. In the 1980s the field had its eyes fixed firmly on the SSC, the Superconducting Supercollider to be constructed in Waxahachie, Texas. After years of design, the go-ahead was given by President Bush in 1988 shortly after his election to construct the huge machine, which was to collide protons with 40 TeV energy. Alas, changes to the design sent costs rising, and, after spending over 2 billion dollars on tunnel boring and lab construction in Texas, the project was canceled by Congress in October 1993.
Those were dark days for particle physics. Any hope of pushing to higher energies seemed to lie in pushing ahead with the design of the LHC at CERN, which had been simmering along but was looking like it would be too little too late if the SSC came on line first. Nevertheless, the Tevatron was just starting to gather significant physics data, and the CDF and D0 experiments would soon discover the top quark, completing the picture of the standard model quarks.
With the SSC out of the picture work on the LHC really began in earnest. The magnet design was finalized and plans for constructing the machine began to gel. It would take many years to complete the engineering, prototyping, and industrialization of the magnet production, and a lot of money. In 1997 the US and CERN reached an agreement (brokered in part by Rep. Sensenbrenner of Wisconsin) whereby the US would contribute about $50 million per year over ten years to the machine itself. This was precedent-setting: never before had the cost of machine construction at CERN, or Fermilab, or SLAC been borne in such large part by a foreign entity. It was essentially the price of admission for the US community to participate in the large experiments ATLAS and CMS, to which the US has committed about half a billion dollars. So though the LHC and the experiments are in Europe, the US has a billion dollar investment in the projects. And now it is time to begin to reap the rewards.
In 1997 it was foreseen to have circulating beams in the LHC by 2005. Construction of the detectors was steady, and it is arguably the case that the experiments were ready before the accelerator. But the completion date of both sets of projects slipped, to 2006, then 2007, and then finally in 2008 all was ready. And, as we all know, in September 2008, after one week of beam commissioning, the LHC suffered a major magnet quench accident which damaged over a kilometer of the machine, necessitating a year-long repair campaign, and a reassessment of the path to the full design energy of 14 TeV.
A large portion if the machine has yet to be retrofit to prevent the type of accident experienced in 2008, but it was decided to operate the collider at 7 TeV and gather physics data in the next year. The energy will open up a new regime to explore for physics beyond the standard model, and we are ready and eager to do just that!
More on the physics in the next post…