Abstract
The detector description is an essential component to analyze data resulting from particle collisions in high energy physics experiments. The interpretation of data from particle collisions typically requires auxiliary data which describe in detail the state of the experiment. These accompanying data include alignment parameters, parameters describing the electronics as well as calibration- and environmental constants. We present a mechanism to manage such data in multiple simultaneous versions depending on their validity. The detector conditions data are made available to the physics algorithms through a number of transient objects grouped to collections. Such a collection represents a coherent slice of all conditions data necessary to process one or several events depending on the valid interval of the slice being the intersection of the individual conditions. A multi-threaded application may hold several such collections in parallel depending on the time-stamps of the events currently processed. Once prepared, these collections are read-only and can easily be shared between threads with minimal requirements for locking and hence minimal overhead. We deliberately restrained ourselves from providing a persistent data solution, which in the past were fields of expertise of the experiments, but rather provided the necessary hooks to populate the conditions cache. We will present the use-cases that have driven the development, the main design choices and details of the implementation.
Highlights
The development of a coherent set of software tools for the description of high energy physics detectors from a single source of information has been on the agenda of many experiments for decades
In this context it is indispensable for data processing applications, which analyze the detector response of particle collisions with high precision to have access to basic detector information such as the geometry, and to other time dependent data
In general each condition is valid for a given period of time, the Interval of Validity (IOV); in practice many or at least several items have the same interval of validity
Summary
The development of a coherent set of software tools for the description of high energy physics detectors from a single source of information has been on the agenda of many experiments for decades In this context it is indispensable for data processing applications, which analyze the detector response of particle collisions with high precision to have access to basic detector information such as the geometry, and to other time dependent data. These data include environmental measurements such as temperatures and pressures used to recalibrate e.g. the response of gaseous sub-detectors, and derived quantities, which may be the result of lengthy computational work such as alignment constants to model geometrical imperfections.
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