Data and simulated data

Latest ATLAS event


The ATLAS collaboration has released 1 inverse femtobarn of data. The ATLAS Open Data datasets are available on this website and on the CERN Open Data portal.

One inverse femtobarn corresponds to approximately 100 trillion proton-proton collisions.

Simulated data

Simulated data, commonly named Monte Carlo (MC), are a key feature for the LHC experiments. These events are simulated using current theoretical models and are used to compare theory with real data.

The full simulation requires the following steps

  • Event generation: Hadronic final states using the proton-proton collisions are generated using programs relying on theoretical calculations, phenomenological models and experimental inputs.

  • Detector Simulation: Interaction of the generated particles inside the ATLAS detector is simulated.

  • Digitisation: The detector response is derived from the particle interactions and it is written in a format compatible with the real output of the detector. In addition, because of the high rate of collisions in the LHC, digitised signals from several simulated events can be piled-up to create samples with a realistic experimental background.

  • Reconstruction: Particle trajectories and energies from the detector are reconstructed. Such final samples are used by the physicists.

Comparing real data and simulated data

Real data and simulated data do not always agree. This can be due to various reasons, such as

  • the conditions not being exactly the same e.g. Energy, pile-up.

  • not all background processes are included in the simulated data,

  • the physics has not been exactly modeled by the theory.

If the data and simulated data does not agree, it is important that physicists understand why.

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