# Laser calibration of the ATLAS Tile Calorimeter during LHC Run 2

## TL;DR

This paper details the laser calibration system for the ATLAS Tile Calorimeter during LHC Run 2, demonstrating its stability, calibration accuracy, and ongoing performance monitoring of photomultiplier tubes.

## Contribution

It introduces the upgraded Laser II calibration system and describes methods to achieve precise calibration and stability for the calorimeter during Run 2.

## Key findings

- Calibration stability better than 0.8%
- Response correction uncertainty of 0.5%
- Effective monitoring of detector performance

## Abstract

This article reports the laser calibration of the hadronic Tile Calorimeter of the ATLAS experiment in the LHC Run 2 data campaign. The upgraded Laser II calibration system is described. The system was commissioned during the first LHC Long Shutdown, exhibiting a stability better than 0.8% for the laser light monitoring. The methods employed to derive the detector calibration factors with data from the laser calibration runs are also detailed. These allowed to correct for the response fluctuations of the 9852 photomultiplier tubes of the Tile Calorimeter with a total uncertainty of 0.5% plus a luminosity-dependent sub-dominant term. Finally, we report the regular monitoring and performance studies using laser events in both standalone runs and during proton collisions. These studies include channel timing and quality inspection, and photomultiplier linearity and response dependence on anode current.