HLT homepage

Maintained by Eric van Herwijnen

Last update: December 16, 2011









The High Level Trigger (HLT) is the second (and last) level of trigger of LHCb, running after the L0 trigger. Its input and output rates are 1MHz and 3KHz respectively. It consists of a C++ application that runs on every CPU of the Event Filter Farm (EFF), which contains between 1000 and 2000 computing nodes. Currently there are 26110 tasks available on the EFF.

The HLT application has access to all detector data in one event, but given the 1 MHz output rate of the L0 trigger and the limited CPU power available, the HLT aims at rejecting the bulk of the events by using only part of the full information which is available.

A brief description of the HLT trigger design can be found here.



Description of the HLT

Notes, presentations and meetings

Performance (old results for HltSys v2r0)


TisTos tool for the HLT

For the developers:

Information on DSTs of benchmark channels

HLT online reference guide

Archive of obsolete material:

Twiki with information for HLT developers (Establish or monitor an alley / add an algorithm / reconstruct …)

Python tools for HLT Studies: modules, scripts, examples Information on HLT for general public