The decay of $B \to J/\psi K_{S,L} $ is often referenced as "golden plate decay", for example in

If there is a B-decay into a CP-eigenstate, like the golden plate decay $B \to J/\psi K_{S,L} $, let [...]

(source: https://www.sciencedirect.com/science/article/pii/S0370269303017258)

Where does this expression come from?


When a particle physics experiment in a collider produces a certain particular outcome whose characteristics are unambiguous and which furnish strong evidence of an important effect or interaction, or direct experimental confirmation of a theoretical prediction, then the physics people refer to that one event as being "gold plated" as in "marvelous", "very valuable", or "totally cool".


The decay $B_d \to J/\psi K^0_s$ was targeted (successfully!) by the BaBar and Belle experiments that first demonstrated that CP violation occurred for B mesons, as predicted by Kobayashi and Maskawa. This is because it contained a single weak phase (so it could be interpreted unambiguously), had a relatively high branching ratio, and had a very clean experimental signature, both the $J/\psi$ and the $K^0_s$ giving sharp mass peaks as well as vertex information. Being so desirable it was therefore known to everybody as the 'gold plated' channel.( see for example the BaBar physics book, page 243 https://slac.stanford.edu/pubs/slacreports/reports19/slac-r-504.pdf)

'Golden plate' I had not heard before - it looks like it has been translated into another language and then back again.

Some people muttered that it was irrational to use the term 'gold plated', which implies that it only looks valuable on the surface. 'Solid gold' would be more accurate. But scientists are not always logical.


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