Since the initial data taking of the CERN LHC, the CMS experiment has undergone substantial upgrades and improvements. This paper discusses the CMS detector as it is configured for the third data-taking period of the CERN LHC, Run 3, which started in 2022. The entire silicon pixel tracking detector was replaced. A new powering system for the superconducting solenoid was installed. The electronics of the hadron calorimeter was upgraded. All the muon electronic systems were upgraded, and new muon detector stations were added, including a gas electron multiplier detector. The precision proton spectrometer was upgraded. The dedicated luminosity detectors and the beam loss monitor were refurbished. Substantial improvements to the trigger, data acquisition, software, and computing systems were also implemented, including a new hybrid CPU/GPU farm for the high-level trigger.

The $\gamma p\to \eta p$ reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold of 707 MeV to 1.4 GeV ($1.49⩽W⩽1.87$ GeV). Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz Microtron MAMI-C and momentum analyzed by the Glasgow tagging spectrometer were used for the $\eta$-meson production. Our accumulation of $3.8\times {10}^6$ $\gamma p\to \eta p\to 3{\pi }^{0}p\to 6\gamma p$ events allows a detailed study of the reaction dynamics. The $\gamma p\to \eta p$ differential cross sections were determined for 120 energy bins and the full range of the production angles. Our data show a dip near $W=1680$ MeV in the total cross section caused by a substantial dip in $\eta$ production at forward angles. The data are compared to predictions of previous SAID and MAID partial-wave analyses and to the latest SAID and MAID fits that included our data.

A search for decays to invisible particles of Higgs bosons produced in association with a top-antitop quark pair or a vector boson, which both decay to a fully hadronic final state, has been performed using proton-proton collision data collected at $${\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V}}$$s = 13 Te V by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 $$\,\text {fb}^{-1}$$fb - 1 . The 95% confidence level upper limit set on the branching fraction of the 125 $$\,\text {Ge}\hspace{-.08em}\text {V}$$Ge V Higgs boson to invisible particles, $${\mathcal {B}({\textrm{H}} \rightarrow \text {inv})}$$B ( H → inv ) , is 0.54 (0.39 expected), assuming standard model production cross sections. The results of this analysis are combined with previous $${\mathcal {B}({\textrm{H}} \rightarrow \text {inv})}$$B ( H → inv ) searches carried out at $${\sqrt{s}=7}$$s = 7 , 8, and 13 $$\,\text {Te}\hspace{-.08em}\text {V}$$Te V in complementary production modes. The combined upper limit at 95% confidence level on $${\mathcal {B}({\textrm{H}} \rightarrow \text {inv})}$$B ( H → inv ) is 0.15 (0.08 expected).