Luminosity Determination in pp Collisions at sqrt(s)=7 TeV Using the ATLAS Detector at the LHC

TL;DR

This paper reports on the measurement and calibration of luminosity in proton-proton collisions at 7 TeV using the ATLAS detector, employing multiple methods to ensure accuracy and consistency.

Contribution

It introduces a multi-method approach for luminosity measurement and calibration in LHC proton collisions, with systematic uncertainty analysis and comparison to event generator predictions.

Findings

Luminosity measurements from different methods agree within 2%.

Residual time- and mu-dependence is less than 2%.

Systematic uncertainty in calibration is +/-11%.

Abstract

Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of mu, the average number of inelastic interactions per bunch crossing. Residual time- and mu-dependence between the methods is less than 2% for 0<mu<2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of +/-11, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most +/-2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation.