Performance of the ATLAS Tile Calorimeter

Abstract

Abstract. The Tile Calorimeter is the central section of the ATLAS hadronic calorimeter at the Large Hadron Collider. It is a key detector for the measurement of hadrons, jets, tau leptons and missing transverse energy. Because of its very good signal to noise ratio it is also useful for the identification and reconstruction of muons. The calibration and performance of the calorimeter have been established through test beam measurements, cosmic ray muons and the large sample of pp collisions. Results on the calorimeter performance are presented, including the absolute energy scale, time resolution, and associated stabilities. The ATLAS Tile CalorimeterThe ATLAS Tile Calorimeter (TileCal) [1] is the central hadronic calorimeter of the ATLAS detector [2] at the Large Hadron Collider (LHC). It is a sampling calorimeter using plastic scintillator tiles as active material and steel plates as absorber. The calorimeter has a total length of 12 m with a diameter of 8.5 m and its total thickness is 7.4 λ int at η = 0. It consists of three cylinders, one long barrel (LB) splitted into two readout partitions, LBA and LBC, and two extended barrels (EBs), EBA and EBC, covering |η| < 1.7.Each barrel is divided into 64 modules in azimuth, φ, giving a granularity of ∆φ ∼ 0.1. A schematic view of a module is shown in Figure 1 (a). Each module is further radially segmented in three layers of readout cells with a granularity of ∆η ∼ 0.1 for the first two layers and ∆η ∼ 0.2 for the third one. The cell segmentation is shown in Figure 1 (b) for a half of LB module and an EB module (LBA and EBA). In total, TileCal has 5182 cells. Each cell is read-out by two photomultiplier tubes (PMTs) from either side of it, except for special cells, via wavelength shifting fibres.TileCal is equipped with several systems to monitor and to calibrate each step of the readout: front-end readout circuit, PMTs and optics. The Charge Injection System [3] injects a well defined charge to the readout electronics to derive ADC to pC conversion factors, C ADC→pC , with 0.7 % precision. The laser system [4] sends light pulses to all the PMTs to monitor the PMT gain of each channels, giving a calibration constant C laser , with 1 ∼ 2 % precision. It is also possible to derive timing constants with the laser system. The optics are monitored by the C S system [5], where a radioactive cesium source traverses through all the tiles in order to equalize the response between individual channels and to monitor stability of optics elements. It gives a calibration constant, C C S , with a e-mail: shima.shimizu@cern.ch 0.3 % precision. The energy deposited in TileCal is reconstructed by applying these calibration constants aswhere E is the reconstructed energy in GeV and A is the signal amplitude in ADC counts. The last constant C pC→GeV is a factor to convert charge to electromagnetic scale energy and was determined from the test beam measurements in 2001-2003 using electron beams [6]. Operation of the Tile Calorimeter in the year 2012In case of a serious failure of on-...