Wing Sheung Chan

The Large Hadron Collider and the ATLAS detector 39 thus have a shorter shower length. For this reason, the EMCal is placed closer to the ID, followed by the hadronic calorimeters. The EMCal has a barrel part that covers | η | < 1 . 475 and two end-caps (EMEC) on both sides of the detector that cover 1 . 375 < | η | < 3 . 2 . All parts of the EMCal use liquid argon (LAr) as the active material and lead plates as absorber. Because of the finer structure of EM showers, the EMCal has a finer granularity than its hadronic counterparts. In most of the covered region, the EMCal has three sampling layers. The first layer has strips of granularity ( ∆ η × ∆ φ ) 0 . 0031 × 0 . 025 which measures η precisely and a thickness of 4.3 radiation lengths ( X 0 ). The second layer contains most of the EMCal materials. It has a granularity of 0 . 025 × 0 . 025 and a thickness of 16 X 0 . The third layer has a coarser granularity of 0 . 05 × 0 . 025 and a thickness of 2 X 0 . Other than the three main sampling layers, the EMCal also has a presampler in the region | η | < 1 . 8 that corrects for energy lost upstream of the detector. The entire EMCal is around 1.5 nuclear interaction lengths thick, meaning that it is mostly transparent to hadrons. The hadronic calorimeters The hadronic calorimeters are designed to induce hadronic showers and measure them. There are three hadronic calorimeters in ATLAS: the scintillator tile calorimeter (TileCal), the LAr hadronic end-cap calorimeter (HEC) and the LAr forward calorimeter (FCal). The tile calorimeter covers the region | η | < 1 . 0 with its barrel and the region 0 . 8 < | η | < 1 . 7 with its extended barrels. It uses scintillating tiles as active material and steel as absorber. Both the barrel and the extended barrels have three layers. From the closest to the beam axis to the farthest, the three layers of the barrel are 1.5, 4.1 and 1.8 interaction lengths ( λ ) thick. For the extended barrels, the three layers are 1 . 5 λ , 2 . 6 λ and 3 . 3 λ thick. The first two layers have a granularity ( ∆ η × ∆ φ ) of 0 . 1 × 0 . 1 while the last layer has a granularity of 0 . 2 × 0 . 1 The hadronic end-cap calorimeter consists of two wheels installed on each side of the detector directly behind the EMEC. The coverage of the HEC slightly overlaps with that of the TileCal and FCal, spanning from | η | = 1 . 5 to | η | = 3 . 2 . Each end-cap wheel has four layers and uses copper plates as active material. The granularity of the HEC is 0 . 1 × 0 . 1 in 1 . 5 < | η | < 2 . 5 and 0 . 2 × 0 . 2 in 2 . 5 < | η | < 3 . 2 . The forward calorimeter is located close to the beam line where it can detect particles in the very forward region 3 . 1 < | η | < 4 . 9 . There are three modules in each end-cap. The module closest to the nominal collision point is made of copper and aims at measuring EM interactions. The remaining two modules are made of tungsten and are devised to measure hadronic interactions. The FCal measures a thickness of approximately 10 λ .