Characterization of new PMTs and fibers for the LUCID-3 prototypes.

Luminosity is a fundamental parameter in collider physics since it is related to cross-sections and collider performances. LUCID-2, the ATLAS luminometer during Run-2, was able to guarantee a precision of $1.7%$ in offline measurements. Similar performances are expected also for Run-3, but the current design will not be able to satisfy the requirement for Run-4. Therefore, a new LUCID must be built. For testing purposes, different prototypes for LUCID-3 were installed and will be used during Run-3. These prototypes use new types of PMTs and new optic fibers that require extensive characterization, from HV-gain profiles to fiber opacification under irradiation, which is the subject of this contribution.