The High Level Trigger and Express Data Production at STAR
Wayne Betts, Jinhui Chen, Yuri Fisyak, Hongwei Ke, Ivan Kisel, Pavel Kisel, Grigory Kozlov, Jeffery Landgraf, Jerome Lauret, Tonko Ljubicic, Yugang Ma, Spyridon Margetis, Hao Qiu, Diyu Shen, Qiye Shou, Xiangming Sun, Aihong Tang, Gene Van Buren, Iouri Vassiliev, Baoshan Xi

TL;DR
The STAR experiment developed a dual real-time data processing framework with a High Level Trigger and Express Data Production system to enable rapid event selection, calibration, and analysis during the Beam Energy Scan phase-II at RHIC.
Contribution
This paper introduces a novel dual real-time framework combining HLT and xProduction for efficient data processing and analysis in high-energy physics experiments.
Findings
Enabled prompt reconstruction of hypernuclei
Demonstrated scalability for high-luminosity experiments
Provided rapid, analysis-ready datasets for collaboration
Abstract
To meet the demands of the Beam Energy Scan phase-II (BES-II) program, the STAR experiment at RHIC developed a dual real-time framework consisting of a High Level Trigger (HLT) and an Express Data Production system (xProduction). The HLT operates online within the Data Acquisition (DAQ) chain on a multicore CPU cluster, with optional acceleration using Xeon Phi coprocessors. It employs parallelized algorithms, such as the Cellular Automaton track finder, for fast tracking, vertexing, and event filtering, enabling real-time event selection and detector monitoring. In parallel, xProduction runs independently of the DAQ loop and performs near offline-quality calibration and reconstruction within hours. Using the express data stream, enhanced by HLT selections, and the STAR calibration framework, it enables early physics analysis and provides collaboration-wide access to analysis-ready…
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