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The aim of the LHCb Upgrade II is to operate at a luminosity of up to 1.5×1034 cm2s−1 to collect a data set of 300 fb−1. The required substantial modifications of the current LHCb electromagnetic calorimeter due to high radiation doses in the central region and increased particle densities are referred to as PicoCal. Modification of the ECAL already during Long Shutdown 3 (LS3) will reduce the occupancy and mitigate substantial ageing effects in the central region after Run 3. Several scintillating sampling ECAL technologies are currently being investigated in an ongoing R&D campaign: Spaghetti Calorimeter (SpaCal) with garnet scintillating crystals and tungsten absorber, SpaCal with scintillating plastic fibres and tungsten or lead absorber, and Shashlik with polystyrene tiles, lead absorber and fast WLS-fibres. Timing capabilities with tens of picoseconds precision 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 SpaCal and Shashlik prototype modules.
S. Kholodenko (Tue,) studied this question.