It sounds like something that should be reported at the Onion, but here I am to tell you that the people who run the CMS detector at the LHC have just released their most recent results. Apparently, if there are extra dimensions, they haven't been hiding anywhere the LHC can find them. To add to the misery of extra dimension hunters, the data from Fermilab's D0 collaboration has also been used to not find extra dimensions.

No, seriously—with the LHC performing so well, the folks at CMS have a huge amount of data. And although the Tevatron is no more, the data remains, and the D0 folk have not been afraid to use it. Between the two of them, they have now eliminated a large range of possibilities when it comes to hidden dimensions, which puts some limits on the imagination of string theorists.

The two detector teams looked for the same signature of extra dimensions using the wave-like nature of particles. Every particle has a wavepacket, which is the wave-like nature of a particle that is confined by the particle's mass and motion to a region surrounding the particle's current location.

When a particle is confined in a box that has dimensions about the same size as its wavepacket, the reflections of the waves from the edges of the box will interfere. This interference pattern means that the particle will only be found in certain places and with certain energies.

If there are extra dimensions (such as in string theory and some other ideas), then the wavepacket should extend into those. If a dimension is curled up on itself, then it will act a bit like a box: any wavepacket that is longer than the dimension will also interfere with itself. Since the particle will only exist in places the wavepacket constructively interferes with itself, only certain particle masses are permitted.

Unfortunately, there are also three spatial dimensions that are, well, rather extended and very much unlike a box. These three dimensions allow the creation of particles with any mass. So, what D0 and CMS were searching for was a tiny blip of particle production at discrete masses on top of a huge and smooth background.

As the mass of particles increases, the length of their wavepacket gets smaller, so heavier particles allow one to see smaller sized dimensions. And for smaller dimensions, particles should appear at wider energy spacings, providing a relatively clear signature for extra dimensions—and, if they appear, we can even tell you how big they are.

Unfortunately, neither CMS or D0 turned up anything for dimensions with a radius of curvature that corresponds to energies below 260GeV for D0 and, depending on various parameters, 2.3-3.8TeV at CMS. I wish I could tell you what that meant in terms of the size of the dimension, but I have no idea.

As with all modern particle physics research, this is all about comparing what you measure to expectations based on the standard model of physics. But in this case, there is a relatively large uncertainty in how particle production couples to the extra dimensions. So the CMS results come with a wide energy range that depends on the unknown physics of the extra dimensions.

Even so, the LHC and Tevatron are still killing off the hopes and dreams of theoretical physicists everywhere. As with all things, we can expect this search to be continued, further narrowing the possible hiding places for extra dimensions.

Physical Review Letters, 2012, DOI: 10.1103/PhysRevLett.108.111801

Physical Review Letters, 2012, DOI: 10.1103/PhysRevLett.108.131802