The Large Hadron Collider (LHC) marked an impressive first on Wednesday 25th July when it accelerated an atom for the first time. The acceleration of the lead ion is hoped to be the first step towards reliable production and study of gamma rays and may eventually lead to the production of never before observed massive particles.
The particle accelerator usually uses protons to create high-energy collisions, a process which led to the discovery of the Higgs Boson. This was the first time that lead atoms, all with a single electron were inserted into the LHC by operators and successfully accelerated.
The achievement is impressive because an atom in this state is extremely delicate, it is difficult to accelerate it without stripping the single electron from the atomic nucleus, a process known as ionisation. The test was also an important step towards CERN’s ‘Physics Beyond Colliders’ project, specifically, it’s ‘GAMMA FACTORY’ concept.
“We’re investigating new ideas of how we could broaden the present CERN research programme and infrastructure,” says Michaela Schaumann, an LHC Engineer in Charge. “Finding out what’s possible is the first step.”
The LHC’s normal operations consist of creating proton-proton collisions. Before the equipment’s winter shutdown, operators replace the protons with atomic nuclei consisting of protons and neutrons. But the real fun starts for a short few days before shutdown during machine development. This is when particle physicists are encouraged to experiment with the LHC a little bit more freely.
During this series of tests, the operators injected groups of lead ions into the LHC and attempted to maintain them in a beam. The first 24 groups of lead ions were maintained in a low-power beam for roughly an hour, the second test of 6 groups was maintained as a beam for 2 hours with the LHC operating at full power.
As mentioned above, the challenge in accelerating atoms is preventing electrons from being stripped. If this happens the atom reacts differently to the magnetic fields which control their trajectory through the LHC. If too many atoms within a beam veer off course and crash into the accelerator’s walls, the LHC ‘dumps’ that beam. This is done to protect the LHC and its magnets.
The aim of these tests is to ascertain if the LHC can be used as a ‘gamma-ray factory’. The process would see accelerated atoms being hit with a laser. This will stimulate the electrons of the atom to jump to a higher energy level. The higher energy state is only temporary, however. When the electron drops down to its previous energy state it emits a photon. The process is known as stimulated emission.
What is different in this circumstance, is that whereas the electron would normally emit a low-frequency and thus low-energy photon, the fact that the atom is travelling through the LHC at near light-speed will cause the wavelength of the emitted photon to ‘squeezed’. As the wavelength is the inverse of the frequency of photons, this also causes an increase in frequency and a subsequent increase in energy. Thus the produced photons would be those of gamma rays.
Researchers hope that these produced gamma-ray beams will be of such high energy that by the equivalence of energy and matter they produce both normal matter particles such as quarks and electrons but also massive particles previously unseen by physicists. This may include the particles which comprise dark matter, the mysterious substance that comprises approximately 80% of all the matter in the observed universe.
Of course, this is a long way from fruition, but the successful acceleration of atoms certainly represents a first step in the correct direction.