Developments of the LHCb ECAL Upgrades

The LHCb electromagnetic calorimeter (ECAL) must be enhanced for Long Shutdown 3 (LS3) and upgraded for Long Shutdown 4 (LS4) to operate at higher luminosity, pile-up and radiation levels. The central region is particularly demanding and requires finer granularity, improved radiation hardness and precision timing. The current strategy combines radiation-tolerant spaghetti calorimeter (SpaCal) modules for the inner ECAL with upgraded Shashlik modules for the outer region. Beam-test results show that LS3 tungsten-absorber SpaCal (SpaCal-W) and lead-absorber SpaCal (SpaCal-Pb) prototypes with plastic fibres satisfy the present energy-resolution target and achieve timing better than 20 ps at high energies. For Upgrade II, a double-section SpaCal-W prototype with gadolinium aluminium gallium garnet (GAGG) crystal fibres reaches a time resolution of (18.5 ± 0.2) ps at 5 GeV while preserving competitive energy resolution. Ongoing research and development (R&D) on absorbers, fibres, light guides and readout supports the feasibility of the future LHCb ECAL upgrade programme.