Speaker
Dr
Simon George
(Royal Holloway)
Description
The High Level Trigger (HLT) of the ATLAS experiment at the Large Hadron Collider
receives events which pass the LVL1 trigger at ~75 kHz and has to reduce the rate to
~200 Hz while retaining the most interesting physics. It is a software trigger and
performs the reduction in two stages: the LVL2 trigger should take ~10 ms and the
Event Filter (EF) ~1 s.
At the heart of the HLT is the Steering software. To minimise processing time and
data transfers it implements the novel event selection strategies of seeded,
step-wise reconstruction and early rejection. The HLT is seeded by regions of
interest identified at LVL1. These and the static configuration determine which
algorithms are run to reconstruct event data and test the validity of trigger
signatures. The decision to reject the event or continue is based on the valid
signatures, taking into account pre-scale and pass-through. After the EF, event
classification tags are assigned for streaming purposes.
Several powerful new features for commissioning and operation have been added:
comprehensive monitoring is now built in to the framework; for validation and
debugging, reconstructed data can be written out; the steering is integrated with the
new configuration (presented separately), and topological and global triggers have
been added.
This paper will present details of the final design and its implementation, the
principles behind it, and the requirements and constraints it is subject to. The
experience gained from technical runs with realistic trigger menus will be described.
Summary
The final version of the software for first LHC collisions will be presented. There
have been major changes, significant experience and a new design drawn up and
implemented since the CHEP '06 paper.
Primary author
Dr
Simon George
(Royal Holloway)
Co-authors
Dr
Andreas Hoecker
(CERN)
Dr
Carlo Schiavi
(INFN, Sezione di Genova)
Christiane Risler
(Humboldt-Universitaet Berlin)
Dr
Gordon Fischer
(Humboldt-Universitaet zu Berlin)
Dr
Jiri Masik
(University of Manchester)
Dr
Joerg Stelzer
(CERN)
Dr
Johannes Haller
(Universitaet Hamburg)
Dr
Martin zur Nedden
(Humboldt-Universitaet zu Berlin)
Dr
Nicolas Berger
(CERN)
Mr
Till Eifert
(Universite de Geneve)
Dr
Tomasz Bold
(University of California, Irvine)
Dr
Valeria Perez Reale
(CERN)
Dr
Xin Wu
(Universite de Geneve)
