LUCID-3: the upgrade of the ATLAS Luminosity detector for High Luminosity LHC

LUCID-2 ($\textbf{LU}$minosity $\textbf{C}$herenkov $\textbf{I}$ntegrating $\textbf{D}$etector) has been the main luminometer for the ATLAS experiment during Run-2 (2015-2018) and Run-3 (2022-ongoing). Offline a precision on the $\mathcal{L}$ measurement for the entirety of Run-2 of 0.8% was achieved, and a similar precision is expected at the conclusion of Run-3. LUCID-2 however will not be able to produce competitive measurements of luminosity in the HL-LHC era, particularly due to the increased number of collisions per bunch crossing. Due to this, an upgrade to LUCID-2, LUCID-3, is under development. Multiple technologies and designs have been proposed, of which prototypes have been produced, installed and have been operating alongside LUCID-2. These prototypes and the results obtained with them are discussed in order to evaluate their potential effectiveness in the HL-LHC.