The DAQ/HLT system of the ATLAS experiment

Abstract

The DAQ/HLT system of the ATLAS experiment at CERN, Switzerland, is being commissioned for first collisions in 2009. Presently, the system is composed of an already very large farm of computers that accounts for about one-third of its final event processing capacity. Event selection is conducted in two steps after the hardware-based Level-1 Trigger: a Level-2 Trigger processes detector data based on regions of interest (RoI) and an Event Filter operates on the full event data assembled by the Event Building system. The detector read out is fully commissioned and can be operated at its full design capacity. This places the responsibility on the High-Level Triggers system to select only events of highest physics interest that will finally reach the offline reconstruction farms. This paper brings an overview of the current ATLAS DAQ/HLT implementation and performance based on studies originated from its operation with simulated, cosmic particles and first-beam data. Its built-in event processing parallelism is presented and discussed.

The ALFA Roman Pot detectors of ATLAS

“…The To reduce these reflections the inner RP windows were subsequently covered by an anti-reflective paint which reduces the amount of reflected light by factors between three and five. 13 The cross talk in neighbouring MAPMT channels is about 4.5 % for the direct neighbours and 1 % for the diagonal neighbours. According to the fibres-to-MAPMT mapping scheme, the cross talk in direct MAPMT channels enhances the amount of hits in a distance of two, eight or ten fibres 13 Deflocculant Acheson Graphite.…”

“…13 The cross talk in neighbouring MAPMT channels is about 4.5 % for the direct neighbours and 1 % for the diagonal neighbours. According to the fibres-to-MAPMT mapping scheme, the cross talk in direct MAPMT channels enhances the amount of hits in a distance of two, eight or ten fibres 13 Deflocculant Acheson Graphite. with respect to the genuine track hit, visible in figure 13.…”

“…In case of a positive decision the data are transferred into the derandomising buffers of the motherboards, otherwise they are dropped. These buffers are the first part of the local DAQ system which provides data aggregation and transfer to the ATLAS-wide ReadOut System (ROS) [13] The data from the buffers are sent via optical links to the ReadOut Drivers (ROD) which are the ATLAS-wide interface between the detector-specific infrastructure and the ROS computers. ALFA utilizes the Muon ROD modules (MROD) which are designed for the ATLAS muon spectrometer [14].…”