Protons are strange

Credit: ATLAS Collaboration/CERN

The four elementary forces of nature are gravitation, electromagnetism, weak nuclear force (or interaction) and strong nuclear force (or interaction), These forces behave like a field with waves, but can be identified as a particle carrying its respective force.

Gravitation is being mediated by the (not yet observed) graviton, predicted in string theory; the other (so called) gauge bosons of the elementary forces are the photon for electromagnetism, the w- and z- boson for the weak nuclear force and the gluon for the strong interaction.

Gravitation we are all familiar with, but is a very weak force compared to the other elementary forces. Just one example: the electromagnetic force is about 10^{38} times stronger than gravitation. Think about a very small magnet able to pick up a paperclip against the gravitational force of the whole Earth at 6 \cdot 10^{25} kg. In string theory this weakness is explained by “dividing” the gravitational force into 6 or more curled up mini-dimensions at the Planck-length, the shortest length to have any relevance under quantum theory (about 6 \cdot 10^{-35} meter). String theory assumes elementary particles to be one dimensional strings, oscillating in and looping through these extra dimensions, hidden from our sight (because they’re small).

Gluons bind the protons and neutrons together in the atomic core and thus carry the strong nuclear interaction; w- and z-bosons carry the weak force. Weak interaction is responsible for radioactive decay.

To know more about these and other particles, particle accelerators smash particles into each other to see what happens. Will other particles appear as a result? What is the energy balance (as it has to even out exactly – no energy wasting in nature)? What behavior do we observe about momentum and spin of particles? Although it’s not clear if a lot of quantum mechanical properties of particles are ‘real’, they do behave like macro-world particles. It’s hardly possible for elementary particles to spin around their axis (if they were little spheres) as their rotation would exceed the speed of light in violation of fundamental laws of nature, but they show behavior that’s exactly the same as in the larger world.

New precision measurements of the W and Z boson cross sections show the proton contains more strange quarks than previously believed.
The protons collided by the LHC are not elementary particles, but are instead made up of quarks, antiquarks and gluons. But, the theory of the strong interactions – quantum chromodynamics (QCD) – does not allow physicists to calculate the composition of protons from first principles. Instead, QCD can connect measurements made in different processes and at different energy scales such that universal properties (“parton density functions” (PDFs)) can be extracted. These determine the dynamic substructure of the proton. … (CERN)

Credit: ATLAS Collaboration/CERN

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