A quick post to advertise a new preprint my collaborators and I put on the arXiv today. It is called “Local Baryon Number at the LHC” and is by me, Joe – one of my PhD students, or Doctoral Researchers, as they are now officially called at UCL – and Pavel and Hridoy, two theory collaborators I’ve enjoyed working before¹, from Case Western Reserve² University. I will explain briefly what we have been doing.

There’s kind of fun mathematical-physics trail that’s been followed to end up with something we can compare to data.

Baryon number is a quantum number carried by quarks (baryons are particles like the proton, made of quarks), and is a global symmetry in the Standard Model. That means if you could somehow magically change baryon number everywhere in the universe, all at once, it would make no observable difference.

Global symmetries are little worrying to me. What do we mean by “all at once”, for example, when relativity tells us there is no unique, universal definition of simultaneity? Local symmetries, on the other hand, are very powerful. Usually referred to as “gauge” symmetries, they underlie the three forces of the Standard Model. The best explanation-by-analogy I could come up with for that is in my book “A Map of the Invsible” / “Atom Land“, and involves a badly-maintained snooker table.

Anyway, the trail being followed goes something like this: Make baryon number into a local symmetry. This introduces a new force, and an extra Higgs boson, but also generates some problems, or “anomalies” in the theory. To get rid of these as simply as possible, you are forced introduce a few other new particles. But one of these turns out to be a good candidate for Dark Matter; and the existence of this new force and these new particles could play a role in solving other issues with the Standard Model, for example how baryons get made in the first place³.

One of the interesting things about this theory is that the new stuff has to really not be too far out of reach in energy if it is going solve these problems, so we might be able to see it experimentally. Or it may be that things we have already measured have ruled it out already. My main goal as a scientist is to measure new things, but the reason for doing that is to test our ideas about the the way physics works. This can be testing the Standard Model itself, or confronting new theories like this one with the data.

So that’s what this paper does, essentially. It scopes out the way these new forces and particles might appear at the Large Hadron Collider (the LHC of the title) and compares those predictions with experiment. In a nutshell, we find several interesting ways the new particles might show up. One of these is in the illustration above, where a Dark Matter particle is produced along with a new exotic particle which travels some distance in the detector before decaying in a pion and another Dark Matter particle.

Some of the possible parameter space for the theory is ruled out already (we use Contur to do this, and the recent tau measurement plays a significant role) but much of it is still viable, and within reach of measurements we could make over the next few years.

Never bet against the Standard Model. But you never know, and there has to be something beyond it. This is, I think, as good a candidate as any. Either way, we should keep measuring.

1. See Dark Matter from Anomaly Cancellation at the LHC and Custodial Symmetry Breaking and Higgs Signatures at the LHC ↩︎
2. This used to confuse me, but there is no Case Western First Team University. This is the top one. ↩︎
3. The first place presumably being the Big Bang. ↩︎