New look at the proton

The spin of a particle can most easily be compared to the rotating movement of a spinning top. In the HERMES experiment at the HERA particle accelerator in Hamburg, physicists are investigating how the spin of protons can be explained by the characteristics of their building blocks: quarks and gluons. Van der Nat investigated a method to measure the contribution of the spin of the quarks to the total spin of the proton, independent of the contribution of the spin of the gluons. For this a quark is shot out of the proton by an electron from the particle accelerator, as a result of which two hadrons are formed. The direction and amount of motion of these two hadrons is accurately measured. This method, which Van der Nat applied for the first time, turned out to be successful.

Figure 1: The HERMES experiment (HERA measurement of spin). This photo shows that the entire experiment is mounted on rails and can be moved out of the ring of the particle accelerator (HERA). At the bottom left of the photo a piece of tube from the accelerator can be seen through which the electrons move (to the right).-Netherlands Organization for Scientific Research