Speaker
Sebastian Neubert
(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, but
resource limitations mean that 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 like for example CDF or D0, 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 20 ms in which to process and accept/reject each event.
In order to minimize systematic uncertainties, the HLT was designed from the outset
to reuse the offline reconstruction and selection code. During the long shutdown it
is proposed to extend this principle and enable the HLT to access offline quality
detector alignment and calibration, by buffering events on the HLT nodes for long
enough for this alignment and calibration to be performed and fed into the HLT algorithms.
This will in turn allow the HLT selections to be tightened and hence will
significantly increase the purity of the data being written for offline analysis.
This contribution describes the proposed architecture of the HLT beyond LS1 and
the technical challenges of implementing a real-time detector alignment and calibration
in the LHC environment.
Authors
Gerhard Raven
(NIKHEF (NL))
Johannes Albrecht
(Technische Universitaet Dortmund (DE))
Vladimir Gligorov
(CERN)
