/sci/ - Science & Math

>>4799050
>only three generations of fermions

Experimental hints that point to three generations. The one which is most unequivocal comes from the Large Electron-Positron (LEP) ring at CERN, the machine which had to be decommissioned in 2000 to leave room for the Large Hadron Collider, due to start slamming protons against protons at 14 TeV this fall. What did LEP find ? Aleph, Delphi, L3, and Opal - the four experiments housed along the LEP beam - detected millions of Z bosons produced in 91 GeV electron-positron collisions in the nineties. By an extremely precise measurement of the Z cross section as a function of beam energy - what is called the Z lineshape – they could determine a parameter of the Z boson called its natural width: the inverse of its lifetime. The Z boson decays to fermion-antifermion pairs, and its lifetime would be significantly shorter than it is if a fourth species of neutrino existed. The LEP experiments were thus able to determine that only three neutrinos exist with a mass smaller than half the Z mass. Below you can see the Z lineshape and the three different curves one would observe if the number of light neutrinos were two, three, or four.

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>>1756416
mfw a fish licks the camera lens of the hydro bot.