Beam-induced and cosmic-ray backgrounds observed in the ATLAS detector during the LHC 2012 proton-proton running period

TL;DR

This paper analyzes beam-induced and cosmic-ray backgrounds in the ATLAS detector during the 2012 LHC run, introducing new methods for background monitoring and detailed correlation studies with beam parameters.

Contribution

It presents novel techniques for monitoring ghost charge and analyzing background sources, improving understanding of background origins during proton-proton collisions.

Findings

Ghost charge can be resolved in individual RF buckets.

Cosmic-ray muon induced fake jets are quantified and compared to simulations.

Background correlations with beam intensity losses are established.

Abstract

This paper discusses various observations on beam-induced and cosmic-ray backgrounds in the ATLAS detector during the LHC 2012 proton-proton run. Building on published results based on 2011 data, the correlations between background and residual pressure of the beam vacuum are revisited. Ghost charge evolution over 2012 and its role for backgrounds are evaluated. New methods to monitor ghost charge with beam-gas rates are presented and observations of LHC abort gap population by ghost charge are discussed in detail. Fake jets from colliding bunches and from ghost charge are analysed with improved methods, showing that ghost charge in individual radio-frequency buckets of the LHC can be resolved. Some results of two short periods of dedicated cosmic-ray background data-taking are shown; in particular cosmic-ray muon induced fake jet rates are compared to Monte Carlo simulations and to the fake jet rates from beam background. A thorough analysis of a particular LHC fill, where abnormally high background was observed, is presented. Correlations between backgrounds and beam intensity losses in special fills with very high $\beta^*$ are studied.