LHC physics? I like it!

When asked why I called the new particle “Higgs like”, rather than just “Higgs”, I used to joke that it’s because I like it. And indeed I do. But now we can confidently drop the ‘like’: this new particle is almost undoubtedly a Higgs.

What leads me to say that with such confidence is the skill and dedication of the Higgs analysis teams from ATLAS and CMS. Over the last few months they have shown that a number of key properties of the new particle all point to it being a Higgs: the way it interacts with other particles agrees with theoretical predictions for a Higgs particle, and its quantum properties of spin and parity are as required for a Higgs.

The question we need to ask now is what kind of Higgs is it? Is it the Higgs of the Standard Model of particle physics? If so, then one of the crowning achievements of 20^th century physics will be complete, with a theory that fully explains the behaviour of the particles that make up the visible Universe, along with all of their interactions with the exception of gravity. Or is it a Higgs boson associated with a theory, such as supersymmetry, that goes beyond the Standard Model, perhaps accounting for some of the 96% of the Universe that is not visible?

This question will take much longer to answer. For now, the analyses of ATLAS and CMS are both fully consistent with a Standard Model Higgs particle, but they are not yet precise enough to differentiate between the Standard Model and theories that go further. It is the precise measurement of the way the new particle interacts with other particles that will allow that differentiation to be made, ultimately letting us know whether we have closed a major chapter in humankind’s exploration of the Universe, or whether we have opened a new one. Either way, it remains very fair to say that I very much like the way that the LHC physics programme is developing.

Rolf Heuer