Characterisation and mitigation of beam-induced backgrounds observed in the ATLAS detector during the 2011 proton-proton run

Aad, G. and Abajyan, T. and Abbott, B. and Abdallah, J. and Khalek, S. A. and Abdelalim, A. A. and Abdinov, O. and Aben, R. and Abi, B. and Abolins, M. and AbouZeid, O. S. and Abramowicz, H. and Abreu, H. and Acharya, B. S. and Adamczyk, L. and Adams, D. L. and Addy, T. N. and Adelman, J. and Adomeit, S. and Adragna, P. and Adye, T. and Aefsky, S. and Aguilar-Saavedra, J. A. and Agustoni, M. and Aharrouche, M. and Ahlen, S. P. and Ahles, F. and Ahmad, A. and Ahsan, M. and Aielli, G. and Krasznahorkay, Attila and Pásztor, Gabriella and Tóth, József (2013) Characterisation and mitigation of beam-induced backgrounds observed in the ATLAS detector during the 2011 proton-proton run. JOURNAL OF INSTRUMENTATION, 8. ISSN 1748-0221

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Abstract

This paper presents a summary of beam-induced backgrounds observed in the ATLAS detector and discusses methods to tag and remove background contaminated events in data. Trigger-rate based monitoring of beam-related backgrounds is presented. The correlations of backgrounds with machine conditions, such as residual pressure in the beam-pipe, are discussed. Results from ded- icated beam-background simulations are shown, and their qualitative agreement with data is eval- uated. Data taken during the passage of unpaired, i.e. non-colliding, proton bunches is used to obtain background-enriched data samples. These are used to identify characteristic features of beam- induced backgrounds, which then are exploited to develop dedicated background tagging tools. These tools, based on observables in the Pixel detector, the muon spectrometer and the calorimeters, are described in detail and their efficiencies are evaluated. Finally an example of an application of these techniques to a monojet analysis is given, which demonstrates the importance of such event cleaning techniques for some new physics searches.

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