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 Ralf Seidl
      To study the strong interaction in nucleon structure and fragmentation


Nucleon spin structure

The spin structure of the nucleon (protons and neutrons) is still only partially understood. While the spin of the proton is of course known to be one half, its composition is still being investigated. In the naive quark-parton model the proton can be described by just three quarks with effective masses of about 1/3 of the proton masses each. Naively, also the spin of the proton was thought to be described by these three constituent quarks with two of the having their spins aligned and one antialigned to add up to the 1/2 of the proton. Hoever, the EMC experiment found that the quark spin contribution is much smaller and currently makes up about only 1/3 of the total proton spin. As the proton is not made up of constituent quarks but nearly masseless quarks, sea-quarks and the mediators of the strong interaction, gluons, all of these can contribute as can orbital angular momentum of them. The goal since the first findings have been to understand the spin decomposition in various high-energy experiments.

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Last modified: November 16, 2017