The LHCb level-2 trigger

The Level-2 trigger algorithm is presented. It is based on a b-lifetime tag, with track impact parameters being measured in the vertex detector and their momenta in the tracking stations. A preliminary study of the trigger performance on Monte Carlo events having already passed the level-0 and -1 triggers, shows that level-2 can achieve a minimum bias rejection factor of about ten, whilst preserving high efficiency for b-signal events.1