A Forward Calorimeter (FoCal) is proposed as an addition to the ALICE experiment, to be installed in the LHC Long Shutdown 3. Its main physics motivation is to provide unique constraints on the low-x gluonic structure of protons and nuclei via forward measurements of direct photons. The unique experimental challenge involved is to discriminate single photons from pairs of very close-by photons originating from pi0 decays. This will require an electromagnetic calorimeter with clean two-shower separation on the mm scale followed by a conventional hadronic calorimeter. The design choice for the electromagnetic part is that of a hybrid SiW sampling calorimeter, using both Si-pad and Si-pixel sensors. Both are challenging technologies, where the Si-pixel based technology is key to the two-shower separation, and will have to go significantly beyond state of the art. An intensive R&D program for both SiW based technologies is ongoing at different laboratories. In this talk I will briefly discuss the physics motivation, the general design concept, and the current performance estimates. I will then report on the status of the R&D projects, including beam test results using a number of prototypes, among them the first full high-granularity digital pixel calorimeter. I will further discuss the future development steps and briefly comment on relations to medical applications of the technology.
Dominik Dannheim (EP-LCD)