The LHCb trigger system: performance and outlook

The LHCb experiment is a spectrometer dedicated to the study of heavy flavor at the LHC. The rate of proton-proton collisions at the LHC is 15 MHz, of which only 5 kHz can be written to storage for offline analysis. The trigger system plays a key role in selecting signal events and rejecting background, and is comprised of a hardware level (L0), reducing the rate to the maxi- mum at which the detector can be fully read out, and a High Level Trigger (HLT) -implemented in software and deployed on a farm of roughly 25000 parallel processing cores- responsible for reducing the rate to the 5 kHz which can be processed offline. The LHCb trigger system allowed LHCb to run at twice its design luminosity in 2012, and performed beyond the nominal design in terms of signal yields. The design and performance of the selection algorithms are discussed in the context of the 2012 data taking, and planned improvements for RunII are presented