# Meet the first 4 quark hadron - Z(c)-3900 **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [June 28, 2013, 4:10pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134 "2013-06-28T16:10:05Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [June 28, 2013, 4:10pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/1 "2013-06-28T16:10:05Z")
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](http://physicsworld.com/cws/article/news/2013/jun/18/charged-charmonium-confounds-particle-physicists). 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 another[article](http://www.sciencenews.org/view/generic/id/351164/description/First_four-quark_particle_may_have_been_spotted) that is a more casual overview. ---
**Author:** ![Typo\_Knig](https://avatars.discourse-cdn.com/v4/letter/t/cdc98d/32.png) [@Typo\_Knig](https://boards.straightdope.com/u/Typo_Knig)\ **Post date:** [June 28, 2013, 5:11pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/2 "2013-06-28T17:11:42Z")
🆒 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. ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [June 28, 2013, 5:23pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/3 "2013-06-28T17:23:02Z")
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](http://www.fnal.gov/pub/today/archive/archive_2013/today13-06-28.html) 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. ---
**Author:** ![QuarkChild](https://avatars.discourse-cdn.com/v4/letter/q/c5a1d2/32.png) [@QuarkChild](https://boards.straightdope.com/u/QuarkChild)\ **Post date:** [June 28, 2013, 11:24pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/4 "2013-06-28T23:24:59Z")
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. ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [June 28, 2013, 11:38pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/5 "2013-06-28T23:38:28Z")
Yeah, I’m fuzzy on that too. But the [day before](http://www.fnal.gov/pub/today/archive/archive_2013/today13-06-27.html) they had this discussion which didn’t mention SUSY by name but . . . > [@](#): > > While top quarks are most commonly produced in pairs via the strong force, the _W_ boson, a weak force carrier, will rarely decay into a solitary top quark (also known as a truth quark) and a bottom (or beauty) quark. Certain models of new physics predict that this mode of single-top quark production would be enhanced with respect to the Standard Model. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [June 29, 2013, 2:27am UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/6 "2013-06-29T02:27:50Z")
An extra quark for Muster Mark! ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [June 29, 2013, 2:20pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/7 "2013-06-29T14:20:38Z")
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](http://en.wikipedia.org/wiki/Pentaquark)) 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](http://cerncourier.com/cws/article/cern/52348) 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_”. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [June 29, 2013, 2:58pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/8 "2013-06-29T14:58:05Z")
Notational clarification: > [@Pasta](#): > > _D_ and _D_\* meson The “\*” in this phrase isn’t for the footnote. It’s a modifier for the _D_, in this case indicating an excited state of the _D_. ---
**Author:** ![deltasigma](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@deltasigma](https://boards.straightdope.com/u/deltasigma)\ **Post date:** [June 29, 2013, 9:25pm UTC](https://boards.straightdope.com/t/meet-the-first-4-quark-hadron-z-c-3900/662134/9 "2013-06-29T21:25:35Z")
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.