The Beam is Back

A little over a year after the highly publicized start-up and break-down of the LHC, the damage has been repaired, new protection systems are in place, and all sectors are cold and ready for beam. Yesterday, the first injection test of 2009 was completed— beams of protons and heavy ions were successfully threaded into the LHC beampipe from its predecessor, the Super Proton Synchrotron (SPS). The beams were allowed to flow as far as the first experiments in both directions, ALICE on the clockwise side, LHCb on the other.

The publicity of the turn-on events will be somewhat more subdued this time around. Of the main steps toward high-energy collisions— first circulating beam, 0.9 TeV collisions (accelerated purely by the SPS), 2.2 TeV collisions (breaking the Tevatron’s world record of 1.96 TeV), and 7 TeV collisions— the media will only be invited for the last; the others will be covered by press releases. Circulating beams are planned for the last week of November, with first collisions and a ramp-up to 2.2 TeV in December, followed by a Christmas break. Holding two 1.1 TeV beams in the ring will only require a modest 2,000 Amp currents in the magnets, far from the 8,500 Amp tests that caused the short last year. Early next year, the machine will be checked-out for running at 7 TeV (6,000 Amps in the magnets). After collecting a sizeable quantity of data and experience, the collision energy will be further raised to something between 8 and 10 TeV. While this might be less exciting than the original plan, it’s great for long-term scientific goals because the four experiments will have a year to calibrate on Standard Model processes and obtain a detailed map of the structure of the proton at smaller and smaller lengths scales (the “parton distribution functions”), which is a crucial factor in many calculations. When we do reach beyond the frontier set by the Tevatron’s collision energy and accumulated dataset, we’ll understand our detectors and the shape of the proton well enough to be sure that what we’re seeing is not just a mistake.

A few weeks ago, I watched PBS’s Journey to Palomar about the building of the Palomar telescope and was rather struck by the parallels with the LHC. Huge crowds flocked to Corning, NY in 1934 to watch the pouring of the glass for its enormous 200-inch mirror, and radio commenters were calling it the most significant event of the 20^th century, including the Great War. Contrary to the opinions of astronomers of the day, many expected the great telescope to finally reveal cities on Mars. At the first pouring, spectators witnessed the result of a miscalculation: the high temperature of the glass melted some of the cores in the mold, causing them to float up to the glass surface, ruining the mirror. A second pouring was attempted months later, closed to the public, and this time it was successful.

The telescope took until 1949 to complete, but when observations began, they revolutionized astronomy. The evolution of stars through the main sequence was finally understood. Cepheid variables measured the distances to galaxies 3 million light years away, allowing us to observe the history of the universe through its expansion. Palomar is still a working instrument, making discoveries today: hopefully the LHC will share the same fate.