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8 June 2012
Image above: Corrections to proton orbits in the LHC appear as regular dips in the instantaneous luminosity measured by CMS (beige) and ATLAS (green). Click for full size (Image: CERN).
The orbits of protons in the 27-kilometre Large Hadron Collider (LHC) have to be adjusted regularly to account for the gravitational effect of the moon.
In the graph above, the two lower curves (in beige and green) show the instantaneous luminosity measured last weekend – when the moon was full – by the two largest detectors at the LHC, CMS and ATLAS. Instantaneous luminosity is a measure of how many collisions happen per second in each experiment between the two beams of protons circulating in opposite directions in the LHC tunnel.
The LHC is so large that the gravitational force exerted by the moon is not the same at all points, which creates small distortions of the tunnel. And the machine is sensitive enough to detect minute deformations created by the small differences in gravitational force across its diameter.
As the moon rises in the sky, the force it exerts changes enough to require a periodic correction of the orbit of the proton beams in the accelerator to adapt to a deformed tunnel. The corrections appear as regular dips in luminosity (see graph above) as the LHC operator adjusts the orbits.
CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.
The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.
Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 20 Member States.
Find out more:
Quatum Diaries: Is the moon full? Just ask the LHC operators: http://www.quantumdiaries.org/2012/06/07/is-the-moon-full-just-ask-the-lhc-operators/
Images, Text, Credit: CERN.