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arXiv 1806.08475hep-exphysics.ins-det
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运行2中在LHC处使用ATLAS触发器进行实时数据分析

Real time data analysis with the ATLAS Trigger at the LHC in Run-2

Pierre-Hugues Beauchemin

摘要:

ATLAS探测器的触发选择能力已显着增强的LHC运行-2,以应付更高的事件率和大量的同时相互作用(堆积)每质子束交叉。一个新的硬件系统,旨在分析实时事件拓扑的水平-1在2017年全面投入使用。预计将于2018年实时使用的基于硬件的轨道重建系统旨在以其全输入速率向高级软件触发器提供轨道信息。高级触发器选择主要依赖于类似离线的重建技术,并且在某些情况下依赖于多变量分析方法。尽管2017年下半年LHC运行突然发生变化,导致堆积增加,因此触发算法的CPU使用率也增加,但由于触发系统的鲁棒性和冗余性,以及与LHC和其他实验一致的调平光度方案的使用,在线运行的触发器组(所谓的触发菜单)只进行了微小的修改。本报告简要而全面地回顾了ATLAS触发系统在2017年的实时性能。将考虑触发器的最相关参数(收集信号的效率和输出数据速率)以及在高级触发器CPU群上实时运行的算法的某些方面的细节。

英文摘要:

The trigger selection capabilities of the ATLAS detector have been significantly enhanced for the LHC Run- 2 in order to cope with the higher event rates and with the large number of simultaneous interactions (pile-up) per protonproton bunch crossing. A new hardware system, designed to analyse real time event-topologies at Level-1 came to full use in 2017. A hardware-based track reconstruction system, expected to be used real-time in 2018, is designed to provide track information to the high-level software trigger at its full input rate. The high-level trigger selections are largely relying on offline-like reconstruction techniques, and in some cases multivariate analysis methods. Despite the sudden change in LHC operations during the second half of 2017, which caused an increase in pile-up and therefore also in CPU usage of the trigger algorithms, the set of triggers (so called trigger menu) running online has undergone only minor modifications thanks to the robustness and redundancy of the trigger system, and the use of a levelling luminosity scheme in agreement with LHC and other experiments. This presentation gives a brief yet comprehensive review of the real-time performance of the ATLAS trigger system in 2017. Considerations will be presented on the most relevant parameters of the trigger (efficiency to collect signal and output data rate) as well as details on some aspects of the algorithms which are run real-time on the High Level Trigger CPU farm.

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