A. Albert's research while affiliated with Brown University and other places

The results of a search for stealth supersymmetry in final states with two photons and jets, targeting a phase space region with low missing transverse momentum ( p T miss ), are reported. The study is based on a sample of proton-proton collisions at s = 13 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb − 1 . As LHC results continue to constrain the parameter space of the minimal supersymmetric standard model, the low p T miss regime is increasingly valuable to explore. To estimate the backgrounds due to standard model processes in such events, we apply corrections derived from simulation to an estimate based on a control selection in data. The results are interpreted in the context of simplified stealth supersymmetry models with gluino and squark pair production. The observed data are consistent with the standard model predictions, and gluino (squark) masses of up to 2150 (1850) GeV are excluded at the 95% confidence level. © 2024 CERN, for the CMS Collaboration 2024 CERN

A combination of the results of several searches for the electroweak production of the supersymmetric partners of standard model bosons, and of charged leptons, is presented. All searches use proton-proton collision data at s = 13 TeV recorded with the CMS detector at the LHC in 2016–2018. The analyzed data correspond to an integrated luminosity of up to 137 fb − 1 . The results are interpreted in terms of simplified models of supersymmetry. Two new interpretations are added with this combination: a model spectrum with the bino as the lightest supersymmetric particle together with mass-degenerate Higgsinos decaying to the bino and a standard model boson, and the compressed-spectrum region of a previously studied model of slepton pair production. Improved analysis techniques are employed to optimize sensitivity for the compressed spectra in the wino and slepton pair production models. The results are consistent with expectations from the standard model. The combination provides a more comprehensive coverage of the model parameter space than the individual searches, extending the exclusion by up to 125 GeV, and also targets some of the intermediate gaps in the mass coverage. © 2024 CERN, for the CMS Collaboration 2024 CERN

Differential cross sections are measured for the standard model Higgs boson produced in association with vector bosons ( W , Z ) and decaying to a pair of b quarks. Measurements are performed within the framework of the simplified template cross sections. The analysis relies on the leptonic decays of the W and Z bosons, resulting in final states with 0, 1, or 2 electrons or muons. The Higgs boson candidates are either reconstructed from pairs of resolved b -tagged jets, or from single large-radius jets containing the particles arising from two b quarks. Proton-proton collision data at s = 13 TeV , collected by the CMS experiment in 2016–2018 and corresponding to a total integrated luminosity of 138 fb − 1 , are analyzed. The inclusive signal strength, defined as the product of the observed production cross section and branching fraction relative to the standard model expectation, combining all analysis categories, is found to be μ = 1.1 5 − 0.20 + 0.22 . This corresponds to an observed (expected) significance of 6.3 (5.6) standard deviations. © 2024 CERN, for the CMS Collaboration 2024 CERN

A bstract A search for a new boson X is presented using CERN LHC proton-proton collision data collected by the CMS experiment at $$ \sqrt{s} $$ s = 13 TeV in 2016–2018, and corresponding to an integrated luminosity of 138 fb − 1 . The resonance X decays into either a pair of Higgs bosons HH of mass 125 GeV or an H and a new spin-0 boson Y. One H subsequently decays to a pair of photons, and the second H or Y, to a pair of bottom quarks. The explored mass ranges of X are 260–1000 GeV and 300–1000 GeV, for decays to HH and to HY, respectively, with the Y mass range being 90–800 GeV. For a spin-0 X hypothesis, the 95% confidence level upper limit on the product of its production cross section and decay branching fraction is observed to be within 0.90–0.04 fb, depending on the masses of X and Y. The largest deviation from the background-only hypothesis with a local (global) significance of 3.8 (below 2.8) standard deviations is observed for X and Y masses of 650 and 90 GeV, respectively. The limits are interpreted using several models of new physics.

A bstract A search is presented for a third-generation leptoquark (LQ) coupled exclusively to a τ lepton and a b quark. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV recorded with the CMS detector, corresponding to an integrated luminosity of 138 fb − 1 . Events with τ leptons and a varying number of jets originating from b quarks are considered, targeting the single and pair production of LQs, as well as nonresonant t -channel LQ exchange. An excess is observed in the data with respect to the background expectation in the combined analysis of all search regions. For a benchmark LQ mass of 2 TeV and an LQ-b-τ coupling strength of 2.5, the excess reaches a local significance of up to 2.8 standard deviations. Upper limits at the 95% confidence level are placed on the LQ production cross section in the LQ mass range 0.5–2.3 TeV, and up to 3 TeV for t -channel LQ exchange. Leptoquarks are excluded below masses of 1.22–1.88 TeV for different LQ models and varying coupling strengths up to 2.5. The study of nonresonant ττ production through t -channel LQ exchange allows lower limits on the LQ mass of up to 2.3 TeV to be obtained.

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.

A search for exotic decays of the Higgs boson (\(\text {H}\)) with a mass of 125\(\,\text {Ge}\hspace{-.08em}\text {V}\) to a pair of light pseudoscalars \(\text {a}_{1} \) is performed in final states where one pseudoscalar decays to two \({\textrm{b}}\) quarks and the other to a pair of muons or \(\tau \) leptons. A data sample of proton–proton collisions at \(\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V} \) corresponding to an integrated luminosity of 138\(\,\text {fb}^{-1}\) recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level (\(\text {CL}\)) on the Higgs boson branching fraction to \(\upmu \upmu \text{ b } \text{ b } \) and to \(\uptau \uptau \text{ b } \text{ b },\) via a pair of \(\text {a}_{1} \)s. The limits depend on the pseudoscalar mass \(m_{\text {a}_{1}}\) and are observed to be in the range (0.17–3.3) \(\times 10^{-4}\) and (1.7–7.7) \(\times 10^{-2}\) in the \(\upmu \upmu \text{ b } \text{ b } \) and \(\uptau \uptau \text{ b } \text{ b } \) final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine upper limits on the branching fraction \({\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} \rightarrow \ell \ell \text{ b } \text{ b})\) at 95% \(\text {CL}\), with \(\ell \) being a muon or a \(\uptau \) lepton. For different types of 2HDM+S, upper bounds on the branching fraction \({\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} )\) are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space, \({\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} )\) values above 0.23 are excluded at 95% \(\text {CL}\) for \(m_{\text {a}_{1}}\) values between 15 and 60\(\,\text {Ge}\hspace{-.08em}\text {V}\).

A bstract A measurement is presented of the primary Lund jet plane (LJP) density in inclusive jet production in proton-proton collisions. The analysis uses 138 fb − 1 of data collected by the CMS experiment at $$ \sqrt{s} $$ s = 13 TeV. The LJP, a representation of the phase space of emissions inside jets, is constructed using iterative jet declustering. The transverse momentum k T and the splitting angle ∆ R of an emission relative to its emitter are measured at each step of the jet declustering process. The average density of emissions as function of ln( k T / GeV) and ln( R/ ∆ R ) is measured for jets with distance parameters R = 0 . 4 or 0.8, transverse momentum p T > 700 GeV, and rapidity | y | < 1 . 7. The jet substructure is measured using the charged-particle tracks of the jet. The measured distributions, unfolded to the level of stable charged particles, are compared with theoretical predictions from simulations and with perturbative quantum chromodynamics calculations. Due to the ability of the LJP to factorize physical effects, these measurements can be used to improve different aspects of the physics modeling in event generators.

A search for W′ bosons decaying to a top and a bottom quark in final states including an electron or a muon is performed with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 138 fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV. Good agreement with the standard model expectation is observed and no evidence for the existence of the W′ boson is found over the mass range examined. The largest observed deviation from the standard model expectation is found for a W′ boson mass (\( {m}_{{\textrm{W}}^{\prime }} \)) hypothesis of 3.8 TeV with a relative decay width of 1%, with a local (global) significance of 2.6 (2.0) standard deviations. Upper limits on the production cross sections of W′ bosons decaying to a top and a bottom quark are set. Left- and right-handed W′ bosons with \( {m}_{{\textrm{W}}^{\prime }} \) below 3.9 and 4.3 TeV, respectively, are excluded at the 95% confidence level, under the assumption that the new particle has a narrow decay width. Limits are also set for relative decay widths up to 30%.