LHC sees first low-energy collisions

The Large Hadron Collider is back in the business of colliding particles. Today low-energy protons met in the hearts of the four Large Hadron Collider experiments. These test collisions will help the ALICE, ATLAS, CMS and LHCb collaborations calibrate their detectors in preparation for the high-energy collisions scheduled for early June. “Our detectors need to be able to distinguish between two particles separated by about the width of a human hair,” says Fermi National Accelerator Laborator...