The LHCb experiment and its upgrades

LHCb is a detector experiment at the Large Hadron Collider dedicated to heavy flavour physics. It was initially proposed for studies of rare decays and CP violation of B mesons, while now its physics program covers CP violation and rare decays of heavy flavour hadrons, spectroscopy and heavy flavour production, W / Z bosons, and heavy-ion physics. The LHCb detector has a tracking system consisting of the vertex locator, a magnet generating magnetic field in the vertical direction, and tracking stations both located upstream and downstream of the magnet. The particle identification at LHCb is provided by two ring imaging Cherenkov counters, calorimeters and muon detectors. The LHCb detector smoothly operated for over 10 years by 2018 in two LHC Runs and accumulated 9 inverse-femtobarn proton-proton collision data on which a plethora of physics results have been published. The high-quality scientific data empowered by excellent tracking and particle- identification performance have profoundly changed the landscape of flavour physics and studies of heavy hadrons. In the operation up to 2018, the LHC beams are adjusted using so-called "luminosity leveling" technique to maintain a stable and relatively low luminosity at the LHCb collision point. During the past Long-Shutdown 2 of the LHC, the LHCb detector has gone through Upgrade I, to enable operation at a luminosity five times of the initial designed value. All subdetectors of the tracking system have been rebuilt using novel technologies, and all other subsystems have gone through major upgrade such as replacement of the whole front-end electronics. The upgraded LHCb detector solved the yield saturation problem of hadronic final states, by completely removing the hardware trigger, allowing for a more flexible and intelligent trigger flow including real-time full event reconstruction. The installation has been completed in 2023, and the experiment is expected to collect data of 50 inverse-femtobarn by end of Run 4 around 2032. The LHC will be upgraded to the High-Luminosity Large Hadron Collider (HL-LHC) before Run 4. In order to fully exploit the potential in flavour physics at the HL-LHC, LHCb is planning an ambitious Upgrade II which will allow further increase of luminosity by a factor of 7.5. The goal of the Upgrade II is to collect a data sample of 300 inverse-femtobarn in the whole lifetime of the LHC, achieving ultimate experimental precision to many key flavour observables such as the CKM parameters, and probing the new physics beyond the Standard Model at an unprecedented sensitivity. With many technical challenges imposed to the detector such as pile-up, high occupancy and radiation damage, the collaboration is redesigning subsystems using the most state-of-the-art technologies and carrying developments for the purpose.