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Experiments at the world’s most powerful particle collider have restarted at CERN, Europe’s particle-physics laboratory, after a three-year upgrade to its machinery. For its third run, the proton beams of the Large Hadron Collider (LHC) will circulate at higher intensities and record energies. Physicists want to use the collisions to learn more about the Universe at the smallest scales, and to solve mysteries such as the nature of dark matter.