On 5 April 2015, after two years of maintenance and upgrades, the Large Hadron Collider (LHC) started up at the collision energy of 13 teraelectronvolts (TeV). The decision to begin the LHC’s second run at 13 TeV has been taken in order to optimise the delivery of particle collisions for physics research, and thereby speed the route to potential new physics. An electronvolt is a unit of energy or mass used in particle physics. One eV is extremely small, and units of a million electronvolts, MeV, or a thousand million electronvolts, GeV, are more common. The LHC will ultimately reach 7 million million electronvolts, or 7 TeV per beam. One TeV is about the energy of motion of a flying mosquito.