Speaker
Heather Russell
(McGill University)
Description
The ATLAS experiment aims at recording about 1 kHz of physics
collisions, starting with an LHC design bunch crossing rate of 40
MHz. To reduce the large background rate while maintaining a high
selection efficiency for rare physics events (such as beyond the
Standard Model physics), a two-level trigger system is used.
Events are selected based on physics signatures such as the presence
of energetic leptons, photons, jets or large missing energy. The
trigger system exploits topological information, as well as
multivariate methods to carry out the necessary physics filtering for
the many analyses that are pursued by the ATLAS community. In total,
the ATLAS online selection consists of nearly two thousand individual
triggers. A Trigger Menu is the compilation of these triggers, it
specifies the physics selection algorithms to be used during data
taking and the rate and bandwidth a given trigger is
allocated. Trigger menus must reflect the physics goals of the
collaboration for a given run, but also take into consideration the
instantaneous luminosity of the LHC and limitations from the ATLAS
detector readout and offline processing farm. For the 2017 run, the
ATLAS trigger has been enhanced to be able to handle higher
instantaneous luminosities (up to 2.0x10^{34}cm^{-2}s^{-1}) and to
ensure the selection robustness against higher average multiple
interactions per bunch crossing.
In this presentation we describe the design criteria for the trigger
menu for Run 2. We discuss several aspects of the process of planning
the trigger menu, starting from how ATLAS physics goals and the need
for detector performance measurements enter the menu design, and how
rate, bandwidth, and CPU constraints are folded in during the
compilation of the menu. We present the tools that allow us to
predict and optimize the trigger rates and CPU consumption for the
anticipated LHC luminosities. We outline the online system that we
implemented to monitor deviations from the individual trigger target
rates and to quickly react to changing LHC conditions and data taking
scenarios. Finally we give a glimpse of the 2017 Trigger Menu,
allowing the listener to get a taste of the vast physics program that
the trigger is supporting.
Primary author
Evelyn Thomson
(University of Pennsylvania)