Crystal Fibers for the LHCb Calorimeter Upgrade

The Large Hadron Collider beauty (LHCb) experiment is one of the four main particle detectors located at the Large Hadron Collider. After the high-luminosity upgrade of the accelerator, the expected radiation dose faced by the LHCb electromagnetic calorimeter will reach peak values of 1 MGy in the centermost part, an amount not tolerable by the currently employed Shashlik technology, which demands a novel radiation hard design. In addition, a time resolution of few tens of picoseconds and a cell lateral size of about 2 cm are planned for track reconstruction purposes by the collaboration. In this article, the crystal spaghetti design was evaluated, a sampling geometry where scintillating crystal fibers are embedded in the dense absorbing material. The prototype was tested at CERN super proton synchrotron (SPS) with muons and electrons measuring an energy resolution of 3% for electrons at 20 GeV, tilting the prototype by 3° both horizontally and vertically with respect to the incident beam, and a time resolution of 79 ps. The results presented in this article show the feasibility of the design.