For the first time ever oxygen ions are currently circulating in the LHC accelerator at CERN in Geneva for special experiments. All detectors are observing this unknown territory in their own way.
In the 21-kilometer-long underground LHC ring, protons are normally accelerated in two directions to nearly the speed of light, after which they collide in the detectors. In the measurement campaign from June 29 to July 9, oxygen will circulate in one direction. Collisions between oxygen ions will also be studied, as well as similar experiments with neon. The CERN physicists jokingly refer to this as “a breath of fresh air” in the accelerator.
The tests are intended to collect measurement data for numerous studies, ranging from cosmic rays to quark-gluon plasma and the strong nuclear force. Until now, apart from protons, experiments with colliding heavy ions have been carried out from time to time, mainly for the Alice experiment.
Exciting
Nikhef is involved in three of the four major detector experiments in the LHC. In addition to Alice, these are ATLAS and LHCb. These days, they are each collecting as much measurement data as possible from the collisions.
The experiments are particularly exciting for Alice. Normally, this experiment, with significant input from Nikhef Utrecht, studies colliding heavy ions. The immense energy involved briefly creates a plasma of quarks and gluons that may also have existed at the time of the Big Bang.
Oxygen is heavier than a proton (the nucleus of hydrogen), but much lighter than lead. The experiments thus shed light on the intermediate area between Alice’s quark-gluon physics and ordinary high-energy physics.
The LHCb detector, also an important Nikhef project, allows argon gas into its detector vacuum at certain moments, causing the proton beam to collide with large molecules that are virtually stationary. Such fixed target experiments provide different insights than colliding beams.
Technically difficult
The experiments with oxygen and neon at CERN were preceded by lengthy preparations. All the LHC’s pre-accelerators and control systems, as well as its superconducting magnets, had to be adjusted to the much heavier particle beams.
The current first run with a proton beam colliding with an oxygen beam is technically the most difficult because the circulating particles differ enormously in mass. Without corrections, the beams would repeatedly collide at different locations instead of precisely at the heart of the detectors. With additional corrections, this is now possible, according to CERN.
