Much has been said about the Higgs boson, mostly how great it would be to find it. But what about if we do not find it? Could that be useful? In fact, yes, that’d be a great discovery.

Finding the Higgs or proving beyond any doubt that it does not exist, will be equally useful as Rolf Heuer, CERN Director General reminded the audience at the recent European Physics Society meeting. The first outcome would be immediately gratifying: job done! But excluding a Higgs boson, at least one of the kind predicted by the Standard Model, our current theoretical model, will put theorists on the right track. What we need is not the Higgs boson per se but understanding how it all works.

The Higgs boson is the simplest solution to the Brout–Englert–Higgs mechanism, a mathematical trick named after the three physicists who developed it. This is what we need to provide mass to all elementary particles such as the electrons, the quarks, and all the heavy bosons we have seen here at CERN and elsewhere, namely, the W and Z bosons. Without this mechanism, the current equations we have to describe elementary particles only produce massless particles. And we know these particles all have a mass, as witnessed countless times in our detectors.

The Brout–Englert–Higgs mechanism also solves another fundamental problem called “unitarity violation”. In simple words, unitarity means that the sum of all probabilities is equal to one. Imagine having marbles of three different colors in a bag. Say we have 20% red ones and 50% yellow ones. I do not need to tell you the remainder, the green marbles, account for 30%. We can all guess that. But if unitarity was violated in this case, the green marbles would account for something different from 30%. The sum of all probabilities would not be 100%. You’d think I was losing my marbles…

This is exactly what theorists know will happen with the sum of all the different ways a particle can decay. They will start being different from one once we look at higher energies. The Brout–Englert–Higgs mechanism stabilizes all that and brings back minimal sanity. Without it, we know all the equations we have to describe the world of elementary particles will cease to work.

This is precisely why theorists are so confident we are bound to find something new with the Large Hadron Collider or LHC. This new accelerator is powerful enough to bring us in the energy regime where we know the equations start failing. So new particles, linked to new layers of the theory we have not yet been able to explore, are bound to show up. They are needed to stabilize the current theoretical framework we have to describe nature. We know something is missing, we simply don’t quite know what this new something might be.

Many models already exist that would preserve unitarity and explain the origin of mass. It needs not be the Standard Model Higgs boson. This is just the simplest explanation. It could be something more complex, in the form of “Technicolor” or extra dimensions. There are many models out there; we simply need to be nudged in the right direction. What we will discover with our detectors will reveal which model is the right one.

Finding the Higgs or not finding it will tell us which way to go.

— Pauline Gagnon

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