Performance of the ATLAS Zero Degree Calorimeter

The ATLAS Zero Degree Calorimeter (ZDC) at the Large Hadron Collider (LHC) is a set of two sampling calorimeter modules symmetrically located at 140m from the ATLAS interaction point. The ZDC covers a pseudorapidity range of |η| <; 8.3 and it is both longitudinally and transversely segmented, thus providing energy and position information of the incident particles. The ZDC is installed between the two LHC beam pipes, in a configuration such that only the neutral particles produced at the interaction region can reach this calorimeter. The ZDC uses Tungsten plates as absorber material and quartz rods interspersed in the absorber as active media. The energetic charged particles crossing the quartz rods produce Cherenkov light, which is then detected by photomultipliers and sent to the front end electronics for processing, in a total of 120 individual electronic channels. The Tungsten plates and quartz rods are arranged in a way to segment the calorimeters in four longitudinal sections. The first section (the one closer to the interaction point) acts as an electromagnetic calorimeter (32X₀) while the remaining three act as a hadronic calorimeter (1.2λ each). Both ZDC arms have the first hadronic module transversely segmented in 24 channels and, in one of the arms, the electromagnetic module is transversely segmented in 64 channels for position information of the incident particles. Each ZDC module individually provides energy and trigger information using a dedicated set of quartz rods that are grouped together and connected to a photomultiplier tube. The ZDC is specially important in heavy ion physics, providing trigger and energy measurements of the spectator neutrons dissociated from the colliding nuclei. In fact, this is the only trigger available for ultra-peripheral interactions where very little activity is present at central rapidities. Besides its role in the heavy ions physics program, the ZDC can also be used to measure the for- ard neutral particle production in low luminosity proton-proton runs.