As the CERN Twitter account helpfully pointed out today, it's been a whopping 40 years since the first experimental evidence for neutral currents was published in the journal Physics Letters. As a key clue in the quest to unify two of the fundamental forces of nature -- electromagnetism and the weak nuclear force -- it's no wonder CERN keeps bringing it up. It could be argued that the magnificent work of the Proton Synchrotron and the Gargamelle bubble chamber (pictured in the excerpt below) marked the transition of particle power across to Atlantic to Geneva.



You see, it wasn't just the discovery of neutral currents that was important. The mathematical unification of the forces relied on understanding the force-carrying particles associated with the weak force. Electromagnetism's massless photon was well understood, but the three gauge bosons of the weak force -- the W+, W- and Z0 -- were thought to have a mass. You could therefore make Ws and Zs if you supplied enough energy, but without knowing the mass (and therefore the energy) of your target boson, you wouldn't know how big to build your accelerator.

And this is where the neutral current experiments could help. Measurements from the Gargamelle experiment gave the hints physicists needed to make such a prediction. CERN took full advantage of these when designing and building the accelerator that would go on to discover the Ws and Z some ten years later, landing two CERN scientists Nobel Prizes almost immediately after.

You can read more about the unification of electromagnetism and the weak force - one of the grand achievements of 20th century science -- in Introducing Particle Physics: A Graphic Guide.