We Could Be About to Break the Standard Model of Physics

Back in December there was an announcement from the folks at the Large Hadron Collider (LHC) at CERN. They tentatively revealed that there had been a ‘bump’ in the data. It was a tentative announcement as they didn’t yet have enough data to say that it was confirmed, they were not yet at the 5 sigma level of certainty, the gold standard level of proof required for a conclusive discovery.

Why, then, bother to announce anything at all? This is the exciting part: if, with the collection of more data, the bump turns out to be real rather than an anomaly then it would break the Standard Model (SM) of physics. This would be HUGE. Bigger than the discovery of the Higgs a few years back.

The SM is the bedrock of modern physics, it is a description of all the particles in the universe along with three of the fundamental forces of nature; the weak nuclear force, the strong nuclear force and electromagnetism. The model was proposed in its current form in the 1970s. Back then some of the particles present in the model were only theoretical, they had never actually been observed. As we have built ever larger particle colliders we have been able to discover these theoretical particles and more firmly etch their place within the model.

The SM has worked surprisingly well; too well, some might say. Whilst it’s great that all those decades ago we were able to make such accurate predictions about the fundamental particles of the universe no one was expecting it to do so perfectly, which is what has happened so far. This is bad because ultimately we want to discover new things, not just confirm what we already suspected.

Below you can see the SM as it stands today.

Note the quantity in the top left portion of each section. It is a number followed by the unit eV/c², this is the mass of the particle in electron volts. Electron volts are a measure of energy but because mass and energy are essentially equivalent it is possible to express the mass of a particle in this way. You can see that the photon has a mass of 0 which is what allows it to travel at the speed of light. Some of the particles are much bigger than the others with masses measured in mega or even giga-electron volts, the famous Higgs boson having a mass of 126 GeV/c² for example.

Let’s get back to the new data. Below you can see the preliminary data from the ATLAS experiment at the LHC. The scale across the bottom is giga-electron volts and the red line is basically what we would expect to see by chance. Around the 700-750 giga-electron volts mark you should see a little bump that deviates from the red line. This is what has gotten all the physicists so excited.

If it is born out then this new particle is huge, both literally and figuratively. 750 GeV is massive in particle terms, more than 4 times the size of the already bulky Higgs boson. But more important than that is the fact that this is completely unexpected. No model currently in existence predicted this, it is new physics and that is incredibly exciting.

Right now the LHC is spending the summer recreating these events and it is hoped that before it closes for the winter it will have gathered enough evidence to confirm that this is real. If they do then you can expect it to be the lead item in the international news that day; if not, then, well, we probably won’t here much at all. I’m really hoping it’s the former.