Spin gymnastics at HERA

The HERA machine at the DESY laboratory in Hamburg is unique among particle accelerators because it collides electrons (or positrons) with protons at high energies. This allows physicists to study the structure of the proton at very short length scales. And when the accelerator starts running again this month, after an 18 week shutdown, it will be able to explore the proton in even greater detail thanks to a new-found ability to study these high-energy collisions using longitudinally polarized positrons.