Someone has run an experiment, and in this experiment they created a large amount of evidence that seems to say that quite an important particle in particle physics weighs something slightly different from what we thought it should.
This is important because the weight of that particle was predicted by our generally-accepted theory of how the universe works. If the weight is different, it means the theory hasn't taken into account everything that it should.
This is important because the weight of that particle was predicted by our generally-accepted theory of how the universe works. If the weight is different, it means the theory hasn't taken into account everything that it should.