The detector nal state is the core element of particle physics analysis as it de nes the physical characteristics that form the basis of the measurement presented in a published paper. Although they are a crucial part of the research process, detector nal states are not yet formally described, published in papers or searchable in a convenient way. This paper aims at providing an ontology pattern for the detector nal state that can be used as a building block for an ontology covering the whole particle physics analysis life cycle.
Particle Physics, the study of the fundamental building blocks and forces of our universe, involves some of the largest experimental apparatus ever constructed, like the ALICE, ATLAS, CMS, and LHCb experiments located at the Large Hadron Collider (LHC) at CERN. Each of these \experiments" is a very large collaboration of physicists who work as a team to design, build, and operate the particle detectors and to produce measurements characterizing the particles that make up the universe. The measurements are inherently statistical in nature: often billions or trillions of particle collisions are analyzed to determine probabilities or probability densities associated with a given physical process. Because many of the experiments collect multi-purpose data, careful attention must be paid to de ning the measurement that is to be made.
Despite the many thousands of papers published since the advent of particle physics in the 1940s, the eld has no formal way of representing or classifying experimental results { no metadata accompanies an article to formally describe the physics result therein. A number of scenarios would be enabled with such a representation. For example, a physicist from ATLAS, or a theorist, could search an external database for previous work done by CMS in order to compare results. Even a physicist inside ATLAS could search an internal database for previous examples similar to a planned analysis; a substantial amount of time and e ort can be saved by starting from some preexisting work.
We intend to address this situation with our ontology design pattern. Results in particle physics take many forms, but all are based on the selection of a target set of characteristics, a detector nal state that de nes the ingredients of the measurement. The fundamental unit of particle physics is the individual interaction of a set of particles, or an \event." An event could, for example, be captured from a single interaction of counter-rotating particles in a collider or from the collision of a high-energy cosmic ray in the atmosphere. The selection characteristics refer to properties of an event and can describe the presence or absence of speci c particles observed by the detector in the aftermath of the collision, or potentially more global properties of the products produced in the collision, such as the total energy released. Since the physics results we wish to describe and preserve in a repository are all based on the selection of one or more detector nal states, this is a necessary ingredient of an ontology covering the whole particle physics analysis life cycle.
Competency questions have been recognized as a good approach to detect and generalize the modeling requirements from multiple domains that an ontology can represent. They are queries that a domain expert would be expected to run against a knowledge base. For the proposed nal state ODP, such competency questions include: 1. Retrieve all analyses requireing particles to have an invariant mass near the
Z pole. 2. Retrieve all analyses that used jets in the nal state. 3. Retrieve all analyses that veto extra leptons. 4. Retrieve all analyses requiring large missing energy. 2
This section presents the detector nal state pattern by discussing the more interesting classes, properties, and axioms. Description Logics (DL) [2] notation is used to present the axioms. To encode the pattern, we make use of the logic fragment SROIQ as de ned in [4], which is the basis for the OWL 2 DL standard [3]. The proposed ODP has been formally encoded using the Web Ontology Language (OWL).1 A schematic view of the pattern is shown in Figure 1. DetectorFinalState: A detector nal state (DetectorFinalState) formally describes and structures information about a physics analysis (measurement) that is de ned by its use of a common set of particle physics characteristics. As such, it must describe those characteristics of the fundamental \event" that have been selected to make the measurement. It is de ned, amongst other features, by a set of particles/objects (PhysicsObjects) contained in the event and by global quantities formed by performing some operation on the ensemble of objects contained 1 The pattern can be downloaded from www.dropbox.com/sh/0upr45j1awd4q0d/AAAw9BQ2eZIWBIh_rBpP1Uu1a?dl=0. in an event (EventLevelQuantity). Both particles/objects and the ensemble measurements are referred to in this pattern as nal state objects (FinalStateObject).
With the following axioms, we enforce that (
In order to select events of interest, these objects are subject to selection criteria that are used to de ne a collection of events that serves as the basis for a physics measurement, and hence must be captured in the pattern. A detector nal state (DetectorFinalState) then conveys numerical information describing the selection. This numerical information is referred as the selection criteria (SelectionCriteria) which models a complex boolean set of unary and binary restrictions. We make use of the classes And and Or to de ne complex selection criteria.
(
(6) (7) In order for these quantities to have meaning, each of the FinalStateObjects requires a BaseDe nition that describes the criteria for the creation of the Final
An example typical selection could be \retrieve all detector nal states involving some electron with pT > 40 GeV." In this case, the selection requires a particular type of nal state object and has a restriction of 40 GeV, a Physical
pT , which is shorthand for the momentum of a particle in the plane transverse to the beam axis. In general, a SelectionCriteria must indeed have a FirstArgument specifying a value and a SecondArgument specifying of which PhysicalQuantity this value is an instance, with some sort of binary operator (< or >, for example) specifying the desired relationship.
For more information as to how information is stored using the pattern see www.dropbox.com/sh/0upr45j1awd4q0d/AAAw9BQ2eZIWBIh_rBpP1Uu1a?dl=0. We not only include terminological axioms in our ontology but also populate the pattern using data from existing publications [1]. 3
This paper proposes a generic ODP to capture the common core of experimental results from particle physics research. More speci cally, it provides a precise description of a detector nal state which can be used to assign meaningful metadata to the output produced by LHC. In future iterations we plan to extend axiomatization and populate it using real-world data to validate its usability.