The LHCb PicoCal

The aim of the LHCb Upgrade II is to operate at a luminosity of up to 1.5 × 1034 cm−2 s−1 to collect a data set of 300 fb−1. The required substantial modifications of the LHCb electromagnetic calorimeter during Long Shutdown 4 (LS4) due to high radiation doses in the central region and increased particle densities are referred to as PicoCal. Several scintillating sampling ECAL technologies are currently being investigated in an ongoing R&D campaign in view of the PicoCal: Spaghetti Calorimeter (SpaCal) with garnet scintillating crystals and tungsten absorber, SpaCal with scintillating plastic fibers and lead absorber, and Shashlik with polystyrene tiles, lead absorber and fast WLS fibers. Timing capabilities with tens of picoseconds precision for neutral electromagnetic particles and increased granularity with denser absorber in the central region are needed for pile-up mitigation. Time resolutions of better than 20 ps at high energy were observed in test beam measurements of prototype SpaCal and Shashlik modules.