The LHCb RICH Upgrade: from design to early performance

<!--HTML--><p>The first year of Run 3 has just concluded and for the LHCb experiment it has been the first chance to take data with the its brand new detectors. During LHC Long-Shutdown 2, the LHCb experiment underwent a major upgrade in order to be able to operate at the instantaneous luminosity of <span style="font-family:&quot;Calibri&quot;,sans-serif;font-size:11.0pt;mso-ansi-language:EN-GB;mso-ascii-theme-font:minor-latin;mso-bidi-font-family:&quot;Times New Roman&quot;;mso-bidi-language:AR-SA;mso-bidi-theme-font:minor-bidi;mso-fareast-font-family:Calibri;mso-fareast-language:EN-US;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;">2×10³³cm⁻²s⁻¹</span> and a reading data rate of 40 MHz with a fully software-based trigger. The RICH system of LHCb has been completely refurbished, installing new photon detectors (Multi-anode Photomultiplier Tubes), equipped with a custom external read-out chain. Furthermore the full optics and mechanics of the RICH1 detector have been redesigned to distribute the Cherenkov photons over a larger surface of the photon detector planes in order to reduce the unprecedented peak occupancy.&nbsp;</p><p>The overview of the RICH upgrade programme across the last decade will be described including the design, installation and commissioning phase. Finally the validation of the newly installed detectors, together with early performance studies from the first year of running, will be presented.</p>