Thursday, July 20, 2017

Has the weak force ever been measured as a force?


Gravitational and electrostatic forces are everyday phenomenon, and continue to be tested by sophisticated experiments at various distances.


Rutherford measured the electrostatic repulsion of alpha particles from nuclei.


At higher incident energies when the projectile energy is sufficient to overcome electrostatic repulsion and distances of a few fermi can be probed, an attractive nuclear force shows up in the angular distribution as well.



But has the weak force ever been measured as a force?


I understand there is some subtleties here, since in quantum mechanical systems (like nuclear scattering for example) we use a potential form (nuclear plus electrostatic) and interpret the angular distribution by propagating an incident wave to get the angular distribution. So I wonder if a deflection in a scattering experiment due to the weak interaction would be good enough even if it might be difficult to interpret as strictly a force.


Related:


Weak force: attractive or repulsive?


Can the weak force create a bound state?


The charges of the forces



Answer



If by "force" you mean a change of energy and momentum but not the type or number of particles involved, then weak neutral currents would be the answer.


These were predicted by Salam, Glashow & Weinberg, and observed by the Gargamelle experiment in 1973. There a particle was observed to start moving, after interacting with an (unobserved) neutrino.


The interaction there is mediated by exchange of a Z boson, which while massive, is uncharged and spin-1, similar to a photon.



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