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The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software. 

The production of 𝜂 and 𝜂′ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of 5.02 and 13TeV and proton-lead collisions are studied at a center-of-mass energy per nucleon of 8.16TeV. The studies are performed in center-of-mass (c.m.) rapidity regions 2.5<𝑦c.m.<3.5 (forward rapidity) and −4.0<𝑦c.m.<−3.0 (backward rapidity) defined relative to the proton beam direction. The 𝜂 and 𝜂′ production cross sections are measured differentially as a function of transverse momentum for 1.5<𝑝T<10GeV and 3<𝑝T<10GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for 𝜂 and 𝜂′ mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of 𝜂 mesons are also used to calculate 𝜂/𝜋0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as 𝜂 and 𝜂′ meson fragmentation. 

Abstract The centrality of heavy-ion collisions is directly related to the created medium in these interactions. A procedure to determine the centrality of collisions with the LHCb detector is implemented for lead-lead collisions at √ s NN = 5 TeV and lead-neon fixed-target collisions at √ s NN = 69 GeV. The energy deposits in the electromagnetic calorimeter are used to determine and define the centrality classes. The correspondence between the number of participants and the centrality for the lead-lead collisions is in good agreement with the correspondence found in other experiments, and the centrality measurements for the lead-neon collisions presented here are performed for the first time in fixed-target collisions at the LHC. 

Abstract The identification of charm jets is achieved at LHCb for data collected in 2015–2018 using a method based on the properties of displaced vertices reconstructed and matched with jets. The performance of this method is determined using a dijet calibration dataset recorded by the LHCb detector and selected such that the jets are unbiased in quantities used in the tagging algorithm. The charm-tagging efficiency is reported as a function of the transverse momentum of the jet. The measured efficiencies are compared to those obtained from simulation and found to be in good agreement. 

Abstract The first search for the doubly heavy baryon and a search for the baryon are performed using collision data collected via the experiment from 2016 to 2018 at a centre-of-mass energy of , corresponding to an integrated luminosity of 5.2 . The baryons are reconstructed via their decays to and . No significant excess is found for invariant masses between 6700 and 7300 , in a rapidity range from 2.0 to 4.5 and a transverse momentum range from 2 to 20 . Upper limits are set on the ratio of the and production cross-section times the branching fraction to ( ) relative to that of the ( ) baryon, for different lifetime hypotheses, at 95% confidence level. The upper limits range from to for the ( ) decay, and from to for the ( ) decay, depending on the considered mass and lifetime of the ( ) baryon.