Too many X’s, Y’s and Z’s?

Abstract

The discoveries in 1974 of the so-called November revolution [1], as the name 'revolution' implies, were not just additions to our knowledge of nature. Instead they signalled a change in our understanding of the structure of matter. Of course, this change did not occur completely overnight. Many of the ideas were there before, accepted by some and doubted by others. As always, there were also plenty of wrong ideas and irrelevant pieces of information. Why were these discoveries so exciting and so significant? First, because those particles were made of an unknown charm quark, and second because the spectrum of such particles could be studied with great precision and it was just the spectrum one would expect on the basis of

Adiabaticity and color mixing in tetraquark spectroscopy

“…Perhaps more promising is the chain b → c + W − → c +c + d giving altogether (ccuūdc) after a uū pair creation. This could lead toD − + X, whereD is an anticharmed meson and X one of the new hidden charm resonances reviewed, e.g., in [18,19]. Another combination is (ccud) + (cū), with, however, a different topology of the quark diagram and thus different color and OZI suppression factors, as discussed by Lipkin in a different context [20].…”