Application of the missing mass method in the fixed-target program of the STAR experiment

Abstract

The search for short-lived particles is usually the final stage in the chain of event reconstruction and precedes event selection when operating in online mode or physics analysis when operating in offline mode. Most often such short-lived particles are neutral and their search and reconstruction is carried out using their daughter charged particles resulting from their decay. The use of the missing mass method makes it possible to find and analyze also decays of charged short-lived particles, when one of the daughter particles is neutral and is not registered in the detector system. One of the most known examples of such decays is the decay Σ− → nπ−. In this paper, we discuss in detail the missing mass method, which was implemented as part of the KF Particle Finder package for the search and analysis of short-lived particles, and describe the use of the method in the STAR experiment (BNL, USA). The method was used to search for pion (π± → μ±ν) and kaon (K± → μ±ν and K± → π±π0) decays online on the HLT farm in the express production chain. An important feature of the express production chain in the STAR experiment is that it allows one to start calibration, production, and analysis of the data immediately after receiving them. Here, the particular features and results of the real-time application of the method within the express processing of data obtained in the BES-II program at a beam energy of 3.85 GeV/n when working with a fixed target are presented and discussed.

The Compressed Baryonic Matter (CBM) Experiment at FAIR – Physics, Status and Prospects

“…This allows for identification of hadrons, light fragments and hypernuclei reconstruction by combining information from all detector sub-systems[106]. These algorithms have been adapted and successfully implemented in STAR experimentʼs express analysis chain for BES-II[107,108]. Moreover, procedures for determining the collision centrality have been developed by using charged particle multiplicities in STS and the energy of spectator fragments in PSD[109,110].…”

Cellular automaton based track finder in the STAR experiment (BNL, USA)

“…This allows the implementation to use more advanced versions of software products as they are developed. So, the KF Particle Finder package, which performs physical analysis of the events, in the HLT is more advanced in relation to the offline version and significantly surpasses it in terms of functionality, including such useful features as the Missing Mass Method [102,103], which makes it possible searching of the short-lived particles which decay into a charged fragment Figure 6.11: Scheme of online data analysis in their express processing on the HLT cluster of the STAR experiment [102]. and a neutron.…”