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

LUCID has been the ATLAS main luminometer for the LHC Run-2 data taking (2015-1018), achieving very good performance (0.8% total uncertainty on luminosity) and a similar performance is expected also for Run-3 (2022-2025). Due to the harsher condition at the HL-LHC, the present LUCID will not be able to operate reliably. Therefore, the detector will be completely redesigned, using both new and proven technologies. Prototype detectors for the new running conditions have already been developed and installed and are under testing for the entire Run-3. They are a PMT-based detector, which uses the quartz window as Cherenkov medium and is positioned further from the beampipe, a low-rate PMT detector, located in the shadow of one of the ATLAS shieldings, and a fiber detector, in which fiber bundles are used as Cherenkov-light emitter and transmitter. In this contribution, the motivations for the redesign of the detector and the first results obtained with the prototypes are discussed.