What data get to travel in high energy physics? The construction of data at the large hadron collider

In present-day high-energy physics experiments, experimenters need to make various judgments in order to design automated data processing systems within the existing technical limitations. In this chapter, as a case study, I consider the automated data acquisition system used in the ATLAS experiment at the Large Hadron Collider (LHC) located at CERN, where the Higgs boson was discovered in 2012. I show that the design of this system involves both theoretical and experimental judgments each of which has different functions in the initial data journey through which usable data are constructed out of collision events detected by the ATLAS detector. I also explore what requirements the foregoing judgments impose on the LHC data in terms of usability, mobility and mutability. I argue that in present-day HEP experiments these aspects of data are distinct but related to each other due to the fact that they are subjected to some common requirements imposed by the theoretical and experimental judgments involved in the design of data acquisition systems.