Operation of the ATLAS end-cap calorimeters at sLHC luminosity: An experimental study

The expected increase of luminosity at sLHC by a factor of ten with respect to LHC luminosities has serious consequences for the signal reconstruction, radiation hardness requirements, and operations of the ATLAS liquid argon calorimeters (EMEC, HEC, FCAL) in the Endcap, respectively forward region. Small modules of each type of calorimeter have been built and exposed to a high intensity proton beam of 50 GeV at IHEP/Protvino [1]. The beam is extracted via the bent crystal technique, offering the unique opportunity to cover intensities ranging from 10⁶ pps up to 10¹² pps. This exceeds the deposited energy per time expected at sLHC by more than a factor of 100. In addition, the machine has been operated with the full RF bunch structure preserved and with 5 empty bunches between filled bunches. Thus the gap between two filled bunches was about 1 ¿s. This operation mode enables the unique opportunity to study the high flux response of the calorimeters not affected by pile-up from previous bunches and to reconstruct a clean signal of the response over the full drift time of electrons in the liquid argon gap. The correlation between beam intensity and the read-out signal has been studied. Also the dependence of the HV currents as well as calorimeter module temperature on the beam intensity has been measured.