W Adam’s research while affiliated with Institut für Hochenergiephysik Wien and other places

A bstract The measurements of the Higgs boson (H) production cross sections performed by the CMS Collaboration in the four-lepton (4 ℓ, ℓ = e , μ) final state at a center-of-mass energy $\sqrt{s}$ = 13 . 6 TeV are presented. These measurements are based on data collected with the CMS detector at the CERN LHC in 2022, corresponding to an integrated luminosity of 34.7 fb − 1 . Cross sections are measured in a fiducial region closely matching the experimental acceptance, both inclusively and differentially, as a function of the transverse momentum and the absolute value of the rapidity of the four-lepton system. The H → ZZ → 4 ℓ inclusive fiducial cross section is measured to be ${2.89}_{-0.49}^{+0.53}{\left({\text{stat}}\right)}_{-0.21}^{+0.29}\left({\text{syst}}\right)$ fb, in agreement with the standard model expectation of ${3.09}_{-0.24}^{+0.27}$ fb.

Data analyses in particle physics rely on an accurate simulation of particle collisions and a detailed simulation of detector effects to extract physics knowledge from the recorded data. Event generators together with a geant -based simulation of the detectors are used to produce large samples of simulated events for analysis by the LHC experiments. These simulations come at a high computational cost, where the detector simulation and reconstruction algorithms have the largest CPU demands. This article describes how machine-learning (ML) techniques are used to reweight simulated samples obtained with a given set of parameters to samples with different parameters or samples obtained from entirely different simulation programs. The ML reweighting method avoids the need for simulating the detector response multiple times by incorporating the relevant information in a single sample through event weights. Results are presented for reweighting to model variations and higher-order calculations in simulated top quark pair production at the LHC. This ML-based reweighting is an important element of the future computing model of the CMS experiment and will facilitate precision measurements at the High-Luminosity LHC.

A bstract A measurement of the top quark pair ( $\textrm{t}\overline{\textrm{t}}$ t t ¯ ) production cross section in proton-proton collisions at a centre-of-mass energy of 5.02 TeV is presented. The data were collected at the LHC in autumn 2017, in dedicated runs with low-energy and low-intensity conditions with respect to the default configuration, and correspond to an integrated luminosity of 302 pb − 1 . The measurement is performed using events with one electron or muon, and multiple jets, at least one of them being identified as originating from a b quark (b tagged). Events are classified based on the number of all reconstructed jets and of b-tagged jets. Multivariate analysis techniques are used to enhance the separation between the signal and backgrounds. The measured cross section is $62.5\pm 1.6{\left(\textrm{stat}\right)}_{-2.5}^{+2.6}\left(\textrm{syst}\right)\pm 1.2\left(\textrm{lumi}\right)$ 62.5 ± 1.6 stat − 2.5 + 2.6 syst ± 1.2 lumi pb. A combination with the result in the dilepton channel based on the same data set yields a value of 62.3 ± 1.5 (stat) ± 2.4 (syst) ± 1.2 (lumi) pb, to be compared with the standard model prediction of ${69.5}_{-3.7}^{+3.5}$ 69.5 − 3.7 + 3.5 pb at next-to-next-to-leading order in perturbative quantum chromodynamics.

A search is presented for fractionally charged particles with charges below 1 e , using their small energy loss in the tracking detector as a key variable to observe a signal. The analyzed dataset corresponds to an integrated luminosity of 138 fb − 1 of proton-proton collisions collected at s = 13 TeV in 2016–2018 at the CERN LHC. This is the first search at the LHC for new particles with a charge between e / 3 and 0.9 e , including an extension of previous results at a charge of 2 e / 3 . Masses up to 640 GeV and charges as low as e / 3 are excluded at 95% confidence level. These are the most stringent limits to date for the considered Drell-Yan-like production mode. © 2025 CERN, for the CMS Collaboration 2025 CERN

A bstract Measurements of fiducial and total inclusive cross sections for W and Z boson production are presented in proton-proton collisions at $\sqrt{s}$ s = 5.02 and 13 TeV. Electron and muon decay modes ( ℓ = e or μ ) are studied in the data collected with the CMS detector in 2017, in dedicated runs with reduced instantaneous luminosity. The data sets correspond to integrated luminosities of 298 ± 6 pb − 1 at 5.02 TeV and 206 ± 5 pb − 1 at 13 TeV. Measured values of the products of the total inclusive cross sections and the branching fractions at 5.02 TeV are σ (pp → W + X) $\mathcal{B}$ B (W → ℓν ) = 7300 ± 10 (stat) ± 60 (syst) ± 140 (lumi) pb, and σ (pp → Z+X) $\mathcal{B}$ B (Z → ℓ ⁺ ℓ − ) = 669 ± 2 (stat) ± 6 (syst) ± 13 (lumi) pb for the dilepton invariant mass in the range of 60–120 GeV. The corresponding results at 13 TeV are 20480 ± 10 (stat) ± 170 (syst) ± 470 (lumi) pb and 1952 ± 4 (stat) ± 18 (syst) ± 45 (lumi) pb. The measured values agree with cross section calculations at next-to-next-to-leading-order in perturbative quantum chromodynamics. Fiducial and total inclusive cross sections, ratios of cross sections of W ⁺ and W − production as well as inclusive W and Z boson production, and ratios of these measurements at 5.02 and 13 TeV are reported.

A bstract A search for heavy, long-lived, charged particles with large ionization energy loss within the silicon tracker of the CMS experiment is presented. A data set of proton-proton collisions at a center of mass energy at $\sqrt{s}$ s = 13 TeV, collected in 2017 and 2018 at the CERN LHC, corresponding to an integrated luminosity of 101 fb − 1 , is used in this analysis. Two different approaches for the search are taken. A new method exploits the independence of the silicon pixel and strips measurements, while the second method improves on previous techniques using ionization to determine a mass selection. No significant excess of events above the background expectation is observed. The results are interpreted in the context of the pair production of supersymmetric particles, namely gluinos, top squarks, and tau sleptons, and of the Drell-Yan pair production of fourth generation ( τ ′) leptons with an electric charge equal to or twice the absolute value of the electron charge ( e ). An interpretation of a Z’ boson decaying to two τ ′ leptons with an electric charge equal to 2 e is presented for the first time. The 95% confidence upper limits on the production cross section are extracted for each of these hypothetical particles.

A bstract The inclusive WZ production cross section is measured in proton-proton collisions at a centre-of-mass energy of 13.6 TeV, using data collected during 2022 with the CMS detector, corresponding to an integrated luminosity of 34 . 7 fb − 1 . The measurement uses multileptonic final states and a simultaneous likelihood fit to the number of events in four different lepton flavour categories: eee, ee μ , μμ e, and μμμ . The selection is optimized to minimize the number of background events, and relies on an efficient prompt lepton discrimination strategy. The WZ production cross section is measured in a phase space defined within a 30 GeV window around the Z boson mass, as σ total (pp → WZ) = 55 . 2 ± 1 . 2 (stat) ± 1 . 2 (syst) ± 0 . 8 (lumi) ± 0 . 3 (theo) pb. In addition, the cross section is measured in a fiducial phase space closer to the detector-level requirements. All the measurements presented in this paper are in agreement with standard model predictions.

A search is presented for the pair production of new heavy resonances, each decaying into a top quark (t) or antiquark and a gluon (g). The analysis uses data recorded with the CMS detector from proton–proton collisions at a center-of-mass energy of 13 $\,\text {Te}\hspace{-.08em}\text {V}$ Te V at the LHC, corresponding to an integrated luminosity of 138 $\,\text {fb}^{-1}$ fb - 1 . Events with one muon or electron, multiple jets, and missing transverse momentum are selected. After using a deep neural network to enrich the data sample with signal-like events, distributions in the scalar sum of the transverse momenta of all reconstructed objects are analyzed in the search for a signal. No significant deviations from the standard model prediction are found. Upper limits at 95% confidence level are set on the product of cross section and branching fraction squared for the pair production of excited top quarks in the $\text {t}^{*} \rightarrow {\text {t}} {\text {g}}$ t ∗ → tg decay channel. The upper limits range from 120 to 0.8 $\,\text {fb}$ fb for a $\text {t}^{*}$ t ∗ with spin-1/2 and from 15 to 1.0 $\,\text {fb}$ fb for a $\text {t}^{*}$ t ∗ with spin-3/2. These correspond to mass exclusion limits up to 1050 and 1700 $\,\text {Ge}\hspace{-.08em}\text {V}$ Ge V for spin-1/2 and spin-3/2 $\text {t}^{*}$ t ∗ particles, respectively. These are the most stringent limits to date on the existence of $\text {t}^{*} \rightarrow {\text {t}} {\text {g}}$ t ∗ → tg resonances.

Nuclear medium effects on B + meson production are studied using the binary-collision scaled cross section ratio between events of different charged-particle multiplicities from proton-lead collisions. Data, collected by the CMS experiment in 2016 at a nucleon-nucleon center-of-mass energy of s NN = 8.16 TeV , corresponding to an integrated luminosity of 175 nb − 1 , were used. The scaling factors in the ratio are determined using a novel approach based on the Z → μ − μ + cross sections measured in the same events. The scaled ratio for B + is consistent with unity for all event multiplicities, putting stringent constraints on nuclear modification for heavy flavor. © 2025 CERN, for the CMS Collaboration 2025 CERN

A bstract A standard model effective field theory (SMEFT) analysis with dimension-six operators probing nonresonant new physics effects is performed in the Higgs-strahlung process, where the Higgs boson is produced in association with a W or Z boson, in proton-proton collisions at a center-of-mass energy of 13 TeV. The final states in which the W or Z boson decays leptonically and the Higgs boson decays to a pair of bottom quarks are considered. The analyzed data were collected by the CMS experiment between 2016 and 2018 and correspond to an integrated luminosity of 138 fb − 1 . An approach designed to simultaneously optimize the sensitivity to Wilson coefficients of multiple SMEFT operators is employed. Likelihood scans as functions of the Wilson coefficients that carry SMEFT sensitivity in this final state are performed for different expansions in SMEFT. The results are consistent with the predictions of the standard model.