Whether it’s 2 mesons or a tetraquark I think is still to be determined, but what makes it especially interesting is that it is electrically charged. Apparently, ‘first order’ mesons are just a quark and its anti-quark. But here, one of the decay products is a charged pion.
There seems to be a lot of excitement about this because of implications it has for non-std physics but I haven’t seen anything that gives any details or seems willing to speculate.
Here’s anotherarticle that is a more casual overview.
Was this in your field? If you’d like to speculate on implications, please do. I’m guessing it has something to do with one of the less elegant versions of supersymmetry since they’re making such a big deal about it having a charge.
In today’s Fermilab news letter they talk about gluinos which apparently are one of the lightest SUSE particles and those are neutral so maybe this makes another version of the theory more likely. IDK.
That’s very interesting news, although I don’t quite see how this relates to beyond the Standard Model physics. This could be important for understanding QCD (the strong interactions), but I haven’t heard of “new physics” models predicting tetraquarks. Of course, it seems like every time there is the barest hint of an experimental signal beyond the SM, immediately a flurry of papers is produced relating it to some SUSY (or other) model. So perhaps we will see some people (not me) connecting the result to SUSY/etc. That would be interesting.
As QuarkChild notes, this doesn’t strain the Standard Model, and there isn’t really a connection to supersymmetry and kin. Rather, the unexpectedness of these states highlights the difficulty in performing QCD calculations at low energy.
We already know experimentally that 2-, 3-, and 6-quark states exist, among others. This new 4-quark state adds an exciting piece of information for the advancement of QCD theory*. And it’s further exciting just from the fact that folks have been looking for such exotica** (as well as finding false positives) for a very long time.
Related to this discovery is the X(3872) state, first observed a decade ago. You might notice the closeness of its mass (3872 MeV) to the one in the OP (3900 MeV). Indeed, the X(3872) is believed by many to be a four-quark particle, but since theoretical guidance is very poor one cannot be completely sure that it’s not just a new cc (charm-anticharm) meson. However, the cc possibility has recently been strongly disfavored by LHCb measurements. It may very well be that X(3872) and Z[sub]c[/sub] are both four-quark states and that we’ve been sitting on one for a decade, unable to confirm it as such because, well, this stuff’s hard. The molecule interpretation, for instance, would have each particle being a bound state of a D and D* meson, just different ones in the two cases.
This doesn’t mean that QCD as a fundamental theory is challenged by these data. Rather, the actual use of QCD to make predictions is tough in this energy regime, so tricks and shortcuts and “effective” models are used, and these all need pressure from experiment in order to improve. The newly state certainly apply said pressure.
** “Exotica” in this context (which you might see in related articles) is just jargon for “bound states of quarks other than the ones we’re most familiar with” rather than “evidence for something outside the scope of the Standard Model”.
For anyone who is interested, while Pasta gives a very good summary of the background involved, the Physics World article I link to in my OP goes into more depth including a discussion of why the charge of the new particle is important.
Thanks for posting, I wouldn’t have heard of this for a long time otherwise. A hot new discovery warms the cockles of this former scientist’s heart.