ALFA detector is part of the ATLAS Roman Pot detector dedicated to measure protons scattered at very small angles. ALFA aims to study elastic and diffractive events in special runs with reduced luminosity and optimized beam optics. Precision of the measurement depends on the correct positioning of the ALFA detector with respect to the actual beam position. For this purpose track-based procedure is used which utilizes tracks of beam halo and elastic protons collected during physics data taking. This poster presents results of fast and robust alignment of ALFA detectors during LHC Run 2. The alignment constants are used in analysis of diffractive events and also serve as preliminary values in elastic analysis. Precise measurements of the elastic cross sections required dedicated more precise measurement

The purpose of the ATLAS Roman Pot (ARP) detector is to measure protons scattered at very small angles. ARP aims to study elastic and diffractive events, exclusive production and photon induced interactions. In LHC Run 2, ARP participated in the ATLAS high-luminosity data taking. In addition, several special runs with reduced luminosity were taken. Any cross section measurement requires good understanding of the particle reconstruction efficiency. This task is particularly complicated in case of forward protons where actual beam condition is important part of the working environment. Modeling of the very forward region in terms of primary particle flux and inactive material producing secondary particle is generally not precise. An overlay technique of MonteCarlo signal events with zero-bias collider data overcomes these difficulties and may provide better understanding of the proton reconstruction efficiency. Proposed plots present results of the proton reconstruction efficiency with the ALFA detector.