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The LHC has two experiments looking for the Higgs boson.

Image: CERN for the ATLAS and CMS Collaborations

A few months ago, scientists from the Large Hadron Collider announced they had found a new particle, one that could be the Higgs boson. The Higgs particle is thought to have properties explaining how other particles have mass. But the first signs of this new particle were detected over a year ago. So why did physicists wait this long to announce the discovery of the Higgs?

The Higgs boson is a very difficult particle to find. The Large Hadron Collider creates Higgs bosons by smashing other particles together at high speeds. Sometimes one of these collisions creates a Higgs particle. However, the Higgs is not stable; it lasts just millionths of a second before breaking down into other particles. It is these other particles that are detected.

Unfortunately, not every collision creates a Higgs boson. Even if one is created, it can be very difficult to tell the difference between the remains of a Higgs boson and the particles from an impact that didn’t create a Higgs. To be sure, scientists ran the experiment lots of times – around one billion collisions every second for over a year.

The scientists also predicted what results they might get if the Higgs particle didn’t exist. The real results were quite different to this prediction. But the scientists weren’t convinced – the difference could be random chance. They got some statisticians to check their results, and found that the chance of getting such different results by luck alone would be one in two million – very unlikely indeed.

Just to be certain, the Large Hadron Collider runs two experiments that look for the Higgs boson. The two experiments are built differently, so they get different types of results. They both detected evidence of a Higgs boson, and more importantly, both experiments agree on how much energy it takes to make a Higgs boson. So we can be very sure that these hardworking scientists have discovered a new particle.

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