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Abstract A Large Ion Collider Experiment (ALICE) has been conceived and constructed as a heavy-ion experiment at the LHC. During LHC Runs 1 and 2, it has produced a wide range of physics results using all collision systems available at the LHC. In order to best exploit new physics opportunities opening up with the upgraded LHC and new detector technologies, the experiment has undergone a major upgrade during the LHC Long Shutdown 2 (2019–2022). This comprises the move to continuous readout, the complete overhaul of core detectors, as well as a new online event processing farm with a redesigned online-offline software framework. These improvements will allow to record Pb-Pb collisions at rates up to 50 kHz, while ensuring sensitivity for signals without a triggerable signature. 

A search is presented for high-mass exclusive diphoton production via photon-photon fusion in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$in events where both protons survive the interaction. The analysis utilizes data corresponding to an integrated luminosity of $103{\mathrm{fb}}^{-1}$collected in 2016–2018 with the central CMS detector and the CMS and TOTEM precision proton spectrometer (PPS). Events that have two photons with high transverse momenta ( $p_{\mathrm{T}}^{\gamma }>100\mathrm{GeV}$), back-to-back in azimuth, and with a large diphoton invariant mass ( $m_{\gamma \gamma }>350\mathrm{GeV}$) are selected. To remove the dominant inclusive diphoton backgrounds, the kinematic properties of the protons detected in PPS are required to match those of the central diphoton system. Only events having opposite-side forward protons detected with a fractional momentum loss between 0.035 and 0.15 (0.18) for the detectors on the negative (positive) side of CMS are considered. One exclusive diphoton candidate is observed for an expected background of 1.1 events. Limits at 95% confidence level are derived for the four-photon anomalous coupling parameters $\left|{\zeta }_1\right|<0.073{\mathrm{TeV}}^{-4}$and $\left|{\zeta }_2\right|<0.15{\mathrm{TeV}}^{-4}$, using an effective field theory. Additionally, upper limits are placed on the production of axionlike particles with coupling strength to photons $f^{-1}$that varies from $0.03{\mathrm{TeV}}^{-1}$to $1{\mathrm{TeV}}^{-1}$over the mass range from 500 to 2000 GeV. © 2024 CERN, for the CMS and TOTEMs Collaboration2024CERN 

The central exclusive production of charged-hadron pairs in $pp$collisions at a center-of-mass energy of 13 TeV is examined, based on data collected in a special high- ${\beta }^{*}$run of the LHC. The nonresonant continuum processes are studied with the invariant mass of the centrally produced two-pion system in the resonance-free region, $m_{{\pi }^{+}{\pi }^{-}}<0.7$or $m_{{\pi }^{+}{\pi }^{-}}>1.8\mathrm{GeV}$. Differential cross sections as functions of the azimuthal angle between the surviving protons, squared exchanged four-momenta, and $m_{{\pi }^{+}{\pi }^{-}}$are measured in a wide region of scattered proton transverse momenta, between 0.2 and 0.8 GeV, and for pion rapidities $\left|y\right|<2$. A rich structure of interactions related to double-pomeron exchange is observed. A parabolic minimum in the distribution of the two-proton azimuthal angle is observed for the first time. It can be interpreted as an effect of additional pomeron exchanges between the protons from the interference between the bare and the rescattered amplitudes. After model tuning, various physical quantities are determined that are related to the pomeron cross section, proton-pomeron and meson-pomeron form factors, pomeron trajectory and intercept, and coefficients of diffractive eigenstates of the proton. © 2024 CERN, for the CMS and TOTEMs Collaboration2024CERN 

A<sc>bstract</sc> A search for the central exclusive production of top quark-antiquark pairs ($$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$) is performed for the first time using proton-tagged events in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 29.4 fb⁻¹. The$$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$decay products are reconstructed using the central CMS detector, while forward protons are measured in the CMS-TOTEM precision proton spectrometer. An observed (expected) upper bound on the production cross section of 0.59 (1.14) pb is set at 95% confidence level, for collisions of protons with fractional momentum losses between 2 and 20%. 

Abstract The Precision Proton Spectrometer (PPS) of the CMS and TOTEM experiments collected 107.7 fb -1 in proton-proton (pp) collisions at the LHC at 13 TeV (Run 2). This paper describes the key features of the PPS alignment and optics calibrations, the proton reconstruction procedure, as well as the detector efficiency and the performance of the PPS simulation. The reconstruction and simulation are validated using a sample of (semi)exclusive dilepton events. The performance of PPS has proven the feasibility of continuously operating a near-beam proton spectrometer at a high luminosity hadron collider. 

Abstract A generic search is presented for the associated production of a Z boson or a photon with an additional unspecified massive particle X,$${\textrm{pp}}\rightarrow {\textrm{pp}} +{{\textrm{Z}}}/\upgamma +{{\textrm{X}}} $$ $\text{pp}\to \text{pp}+\text{Z}/\gamma +\text{X}$, in proton-tagged events from proton–proton collisions at$$\sqrt{s}=13\, \textrm{TeV}$$ $\sqrt{s}=13\text{TeV}$, recorded in 2017 with the CMS detector and the CMS-TOTEM precision proton spectrometer. The missing mass spectrum is analysed in the 600–1600 GeV range and a fit is performed to search for possible deviations from the background expectation. No significant excess in data with respect to the background predictions has been observed. Model-independent upper limits on the visible production cross section of$${\textrm{pp}}\rightarrow {\textrm{pp}} +{{\textrm{Z}}}/\upgamma +{{\textrm{X}}} $$ $\text{pp}\to \text{pp}+\text{Z}/\gamma +\text{X}$are set.