The Standard Model has worked beautifully to predict what experiments have shown so far about the basic building blocks of matter, but physicists recognize that it is incomplete. Supersymmetry is an extension of the Standard Model that aims to fill some of the gaps. It predicts a partner particle for each particle in the Standard Model. These new particles would solve a major problem with the Standard Model – fixing the mass of the Higgs boson. If the theory is correct, supersymmetric particles should appear in collisions at the LHC.
At first sight, the Standard Model seems to predict that all particles should be massless, an idea at odds with what we observe around us. Theorists have come up with a mechanism to give particles masses that requires the existence of a new particle, the Higgs boson. However, it is a puzzle why the Higgs boson should be light, as interactions between it and Standard-Model particles would tend to make it very heavy. The extra particles predicted by supersymmetry would cancel out the contributions to the Higgs mass from their Standard-Model partners, making a light Higgs boson possible. The new particles would interact through the same forces as Standard-Model particles, but they would have different masses. If supersymmetric particles were included in the Standard Model, the interactions of its three forces – electromagnetism and the strong and weak nuclear forces – could have the exact same strength at very high energies, as in the early universe. A theory that unites the forces mathematically is called a grand unified theory, a dream of physicists including Einstein.
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