From Beam to Particle

• At the beginning of the particle journey, it starts with a negative hydrogen ion beam in the Linac 4. Just like the protons that go to the LHC, it all starts with a humble bottle of hydrogen. Hydrogen anions are accelerated in Linac 4 and upon injection in the PS booster the electrons are stripped away and the protons continue into the accelerator complex. To produce antiprotons, we smash the proton beam into a proton rich metal target (iridium). In this collision, secondary particles get created, including among other things antiprotons.
• These antiprotons get directed to the Antiproton Decelerator (AD), where they can be slowed down to about 10% of the speed of light and sent to one of many experiments in the antimatter factory.
• A new element in the journey of the Antiproton is the ELENA-Ring (Extra Low Energy Antiproton). It’s a new decelerator, that is capable of slowing antiprotons down even further than the AD (to about 1.5% of the speed of light). ELENA opens two new possibilities: The first one is that every experiment in the Antimatter Factory can get antiprotons and don’t have to wait for the particle beam because another experiment is currently measuring. And the second and more important thing is, that we get the antiprotons at a much lower kinetic energy, increasing the efficiency with which we can catch and cool them. Ultimately giving us more experimental time and more antihydrogen!

Why decelerate?

In order to make (anti)matter from “nothing” you need as a minimum the energy given by Einstein's famous formula E=mc². In practice you need somewhat more to make the process efficient. Antiproton production therefore requires high energy (10s of GeV) collisions (proton beam onto a metal target), and thus collision products are also fast.

Normally, every accelerator at CERN does accelerate (as the name indicates). But for our experiments, we run an accelerator backwards (a decelerator). Slow antiprotons are easier for us to catch in our trap, and by catching them we can observe and manipulate them much more precisely than if they were in a beam.

More about antimatter and its history at CERN, you can find here.