Horrible title! [1] [2] There is no box.

They are studing the formation of particles formed by a charm quark and an anti-charm quark, called "charmonium".

In their simulations they get a version of "charmonium" that is not rotaing, and also a version that is rotating. The non-rotating and the rotating version have different properties, in particular the mass. It's part of the weird quantum mechanics properties. (I'm skiping some details, in part becuse they are very complicated, in part becuse I don't remember them and in part becuse I never knew them.) IIUC the different mass agree with the mass obtained in experimental results.

The exact calculations with quarks are extremly complicated, so they use in a computer a standart method that use a grid/array to simulate a small region of the universe. Since the grid represents a small cube, the press release decided to call it a box.

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[1] It's the original title as asked in the guidelines. This is not a complain agaisnt the OP, but a complain agaisnt whoever wrote the press release.

[2] The titles of the research papers are:

* Scalar and Tensor Charmonium Resonances in Coupled-Channel Scattering from Lattice QCD

* Charmonium and resonances in coupled-channel scattering from lattice QCD

I think both are fine. For HN I'd prefer a shorter version "Charmonium and resonances in scattering from lattice QCD" because in this short version I can imagine what every word means.