Speakers
Christoph Michael Langenbruch
(CERN)
Christoph Michael Langenbruch
(CERN)
Description
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 analytsis. For this reason the
LHCb data acquisition system -- trigger -- plays a key role in selecting signal
events and rejecting background. In contrast to previous experiments at hadron
colliders, the bulk of the LHCb trigger is implemented in software and deployed
on a farm of 20k parallel processing nodes. This system, called the High Level
Trigger (HLT) is responsible for reducing the rate from the maximum at which the
detector can be read out, 1.1 MHz, to the 5 kHz which can be processed offline,
and has, on average, 20 ms to decide whether to accept an event. The inherent
flexibility of this software trigger allowed LHCb to run at twice its design
instantaneous luminosity in 2012. Simultaneously, the HLT performed far beyond
the nominal design in terms of signal efficiencies, in particular for charm
physics. It also showcased a number of pioneering concepts, for example : the
deployment of an inclusive multivariate B-hadron tagger as the main physics
trigger of the experiment, buffering of events to local disks in order to
leverage the otherwise idle resources when the LHC does not produce collisions,
and simulation-free event-by-event trigger efficiency corrections. This talk
will cover the design and performance of the LHCb trigger system, and discuss
planned improvements beyond LS1, in particular plans for real-time detector
alignment and calibration in order to allow the trigger to perform offline
quality selections, as well as plans for the LHCb upgrade trigger.
Primary authors
Gerhard Raven
(NIKHEF (NL))
Johannes Albrecht
(Technische Universitaet Dortmund (DE))
Vladimir Gligorov
(CERN)
