Performance of the 3D pixel tracker of the CMS Precision Proton Spectrometer and search for Anomalous Quartic Gauge Couplings in exclusive vector boson pair production with proton tagging

<!--HTML-->The Precision Proton Spectrometer (PPS) of the Compact Muon Solenoid(CMS) experiment at the Large Hadron Collider (LHC) is a near-beam magnetic spectrometer that measures protons surviving the collision in the CMS interaction point (IP). Because of the LHC magnetic fields, protons that lost part of their energy in the interaction are bent outside the beam envelope and can be detected. Located ~ 200 m away from the IP on both sides of CMS, the PPS stations provide a tracking and timing measurement of the outgoing protons, thus determining their kinematic properties.<br>This valuable information represents a unique extension of the physics capabilities of CMS, as it allows the entire final state of central exclusive production (CEP) events to be reconstructed. In fact, CEP consists in processes which produce a central state while the protons survive the interaction. The central state kinematics, reconstructed with the CMS detectors, can thus be matched with the ones inferred from the proton measurement and used to effectively identify CEP events.<br>The PPS has taken data during Run 2 (2016-2018), collecting more than 100 fb$^{-1}$ of integrated luminosity. During operation the detector is subject to a high and non-uniform irradiation. To cope with this, the tracking detectors were equipped with 3D silicon pixel sensors, read out by the chips developed for the Phase I upgrade of the CMS central pixel tracker. Because of the non-uniform radiation damage in the readout chips, a thorough characterization of the tracking efficiency along the data-taking was carried out, followed by extensive studies of the PPS proton reconstruction performance.<br>The PPS will take data in Run 3 (2022-2025), with completely new detectors. The tracker will be equipped with a new type of 3D silicon pixel sensors and different readout. The detector has been characterised and integration tests have been performed in preparation of the data-taking. An innovative movement system has been designed and implemented, which will allow to spread the irradiation across the detectors, making it more uniform and effectively extending their lifetime. The detector has recently been installed and is currently under commissioning.<br>A search for anomalous quartic gauge couplings (AQGC) in exclusive vector boson pair production with proton tagging has been performed with Run 2 data. The decay channel in which both vector bosons decay into quarks, which are reconstructed as a single large-radius jet because of their Lorentz boost, has been studied. No excess with respect to the Standard Model predictions has been detected and limits on dimension-6 and dimension-8 AQGC effective field theory couplings have been set.