If we look at the table over mediator particles, there is another thing that differs the weak force from the others, the fact that the W- and Z-bosons have masses.
This is because of the ingenius Higgs mechanism. By introducing a new field, this time a spinless field, it turns out that the characteristics of vacuum changes! A photon travelling in vacuum may, for example, spontaniously create an electron-positron pair that later annihilates into a photon again.
By, in a similar way, interacting with a neutral Higgs field on their way through vacuum, the W- and Z-bosons "feel" a "resistance." This means that they become massive. This explanation is, so far, the only one that explains the masses of the W- and Z-bosons. The ultimate evidence that this is the correct answer to the problem with masses would be if spinnless Higgs particles could be found experimentaly. At all new accelerators the searching for Higgs particles has a high priority. Already, experiments at the LEP-accelerator at CERN outside Geneva have shown that if the Higgs particle exists, it has to be heavier than approximately 90 GeV.
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