Marco Ferrero

A measurement of the Z γ production cross section in proton-proton collisions at a center-of-mass energy of 13.6 TeV is presented. Data corresponding to an integrated luminosity of 34.8 fb − 1 , collected by the CMS experiment at the LHC in 2022 are used. Events with an oppositely charged pair of muons or electrons, with an invariant mass corresponding to a Z boson, together with an isolated photon are selected. The measured fiducial cross section for the combined electron and muon channels is 1.896 ± 0.033 ( stat ) ± 0.054 ( syst ) ± 0.006 ( theo ) pb , in agreement with the standard model prediction of 1.922 ± 0.094 pb . Constraints on neutral triple gauge couplings generated by dimension-8 operators in a recently proposed effective field theory framework are determined for the first time.

A bstract: Event shape variables, constructed from the four-momenta of the final-state objects in an event, are sensitive to the predictions of quantum chromodynamics in multijet production. A measurement of five event shape variables is presented, using proton-proton collision data collected at a centre-of-mass energy of 13 TeV with the CMS detector during 2016–2018, corresponding to an integrated luminosity of 138 fb ^{− 1} . The variables are evaluated using the charged particles inside jets. After correcting for detector effects, their distributions are compared with the predictions from several models for multijet production. Overall, there is general agreement between several theoretical predictions and the data with scope for improvement of our understanding of QCD at different energy scales.

A bstract: A search is performed for dark matter produced in association with bottom quarks and a pair of electrons or muons in data collected with the CMS detector at the LHC, corresponding to 138 fb ^{− 1} of integrated luminosity of proton-proton collisions at a center-of-mass energy of 13 TeV. For the first time at the LHC, the associated production of a bottom quark-antiquark pair and a new heavy neutral Higgs boson (H) that subsequently decays into a leptonically decaying Z boson and a pseudoscalar (a) is explored. The latter acts as a dark matter mediator in the context of the two Higgs doublet model plus a pseudoscalar (2HDM+a). Multivariate techniques that target a wide range of mass configurations for the H and a particles are used. The observations are consistent with the expectations from standard model processes. Upper limits at 95% confidence level are set on the product of cross section and branching fraction of the new particles, ranging from 10 ^{− 2} pb for an H mass of 400 GeV to 10 ^{− 3} pb for an H mass of 2000 GeV. Constraints on the parameter space of a benchmark 2HDM+a model are derived and compared with expectations in the context of cosmological predictions.

Measurements of the spin correlation coefficients in the beam basis are presented for top quark-antiquark ( t t ¯ ) systems produced in proton-proton collisions at s = 13 TeV collected by the CMS experiment in 2016–2018, and corresponding to an integrated luminosity of 138 fb − 1 . The t t ¯ system is reconstructed from final states containing an electron or muon and jets. Together with the previously reported results in the helicity basis, these measurements are used to decompose the system into the Bell and spin eigenstates in various kinematic regions. The spin correlation coefficients are also used to evaluate properties of the t t ¯ quantum state, such as the purity, von Neumann entropy, and entanglement. All results are consistent with standard model predictions.

The macroscopic electrical response of small-pitch50 × 50 μm ² 3D pixel sensors was investigated by comparing experimental measurements with TCAD simulations. Selected trap parameters (introduction rates and capture cross sections) of the CERN (Folkestad) model, originally developed for fluences up to 8 × 10 ¹⁵ n _eq /cm ² , were varied to study their impact on the simulated characteristics and to assess the sensitivity in reproducing the measured behaviour. The analysis focuses on the I-V, C-V, and charge collection efficiency (CCE) characteristics at fluences of 1 × 10 ¹⁶ n _eq /cm ² and 2.5 × 10 ¹⁶ n _eq /cm ² . This work highlights how variations in trap parameters influence the performance of irradiated 3D sensors and supports the extension of the CERN model for 3D detectors operating at high fluence.