233 Search Results

In the standard model of particle physics, the masses of the carriers of the weak interaction, the W and Z bosons, are uniquely related. Physics beyond the standard model could change this relationship through the effects of quantum loops of virtual particles, thus making it of great importance to measure these masses with the highest possible precision. Although the mass of the Z boson is known to the remarkable precision of 22 parts per million (2.0 MeV), the W boson mass is known much less precisely, given the difficulty of the measurement. A global fit to electroweak data, used to predict the W boson mass in the standard model, yields an uncertainty of 6 MeV. Reaching a comparable experimental precision would be a sensitive and fundamental test of the standard model. Furthermore, a precision measurement of the W boson mass performed by the CDF Collaboration at the Fermilab Tevatron has challenged the standard model by significantly disagreeing with the prediction of the global electroweak fit and the average of other $$m_\mathrm{W}$$ measurements. We report the first W boson mass measurement by the CMS Collaboration at the CERN LHC, based on a data sample collected in 2016 at the proton-proton collision energy of 13 TeV. The W boson mass is measured using a large sample of W$$\to\mu\nu$$ events via a highly granular binned maximum likelihood fit to the kinematic properties of the muons produced in the W$$^{+}$$ and W$$^{-}$$ boson decays. The significant in situ constraints of theoretical inputs and their corresponding uncertainties, together with an accurate determination of the experimental effects, lead to a precise W boson mass measurement, $$m_\mathrm{W} =$$ 80$$\,$$360.2 $$\pm$$ 9.9 MeV, in agreement with the standard model prediction.

A search for heavy neutral gauge bosons (Z') decaying into a pair of tau leptons is performed in proton-proton collisions at $$\sqrt{s}$$ = 13 TeV at the CERN LHC. The data were collected with the CMS detector and correspond to an integrated luminosity of 138 fb$$^{-1}$$. The observations are found to be in agreement with the expectation from standard model processes. Limits at 95% confidence level are set on the product of the Z' production cross section and its branching fraction to tau lepton pairs for a range of Z' boson masses. For a narrow resonance in the sequential standard model scenario, a Z' boson with a mass below 3.5 TeV is excluded. This is the most stringent limit to date from this type of search.

This paper presents a model-agnostic search for narrow resonances in the dijet final state in the mass range 1.8-6 TeV. The signal is assumed to produce jets with substructure atypical of jets initiated by light quarks or gluons, with minimal additional assumptions. Search regions are obtained by utilizing multivariate machine-learning methods to select jets with anomalous substructure. A collection of complementary anomaly detection methods - based on unsupervised, weakly supervised, and semisupervised algorithms - are used in order to maximize the sensitivity to unknown new physics signatures. These algorithms are applied to data corresponding to an integrated luminosity of 138 fb$$^{-1}$$, recorded by the CMS experiment at the LHC, at a center-of-mass energy of 13 TeV. No significant excesses above background expectations are seen. Exclusion limits are derived on the production cross section of benchmark signal models varying in resonance mass, jet mass, and jet substructure. Many of these signatures have not been previously sought, making several of the limits reported on the corresponding benchmark models the first ever. When compared to benchmark inclusive and substructure-based search strategies, the anomaly detection methods are found to significantly enhance the sensitivity to a variety of models.

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$$\mu$$, $$\mu\mu $$e, and $$\mu\mu\mu$$. 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 $$\sigma_{\text{total}}$$(pp$$\to$$WZ) = 55.2$$\pm$$1.2 (stat) $$\pm$$1.2 (syst) $$\pm$$0.8 (lumi) $$\pm$$0.1 (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.

In system prognostics and health management, multivariable degradation models have been widely developed to predict the life of complex systems using degradation data of multiple Performance Characteristics (PCs). Recent studies have detected a Long-Term Memory (LTM) effect among the degradation process of various PCs, implying a strong coupling phenomenon between the future degradation behavior and historical degradation trajectory. Although the LTM has been widely integrated into single-PC-based degradation modeling, it has not been considered in multi-PC-based scenarios. To capture LTM among multiple PCs, this article proposes a novel LTM-integrated Multivariate Degradation Model (MDM) for system life prediction based on multivariate fractional Brownian motion, which simultaneously incorporates the cross-correlation among different PCs. To estimate parameters of the LTM-integrated MDM, a maximum likelihood method is developed. Here, two likelihood-ratio hypothesis tests are developed to test the existence of the overall and individual LTM effect among multiple PCs. Both simulation studies and physical experiments on the performance degradation of solar energy conversion and storage devices are conducted to validate the proposed model. Results reveal that the proposed LTM-integrated MDM significantly outperforms existing MDMs in life prediction, while the lifetime uncertainty is heavily underestimated by those traditional approaches that neglect the LTM.

A direct search for new heavy neutral Higgs bosons A and H in the $$\mathrm{t\bar{t}}$$Z channel is presented, targeting the process pp $$\to$$ A $$\to$$ ZH with H $$\to$$$$\mathrm{t\bar{t}}$$. For the first time, the channel with decays of the Z boson to muons or electrons in association with all-hadronic decays of the $$\mathrm{t\bar{t}}$$ system is targeted. The analysis uses proton-proton collision data collected at the CERN LHC with the CMS experiment at $$\sqrt{s}$$ = 13 TeV, which correspond to an integrated luminosity of 138 fb$$^{-1}$$. No signal is observed. Upper limits on the product of the cross section and branching fractions are derived for narrow resonances A and H with masses up to 2100 and 2000 GeV, respectively, assuming A boson production through gluon fusion. The results are also interpreted within two-Higgs-doublet models, complementing and substantially extending the reach of previous searches.

The TOTEM Roman pot detectors are used to reconstruct the transverse momentum of scattered protons and to estimate the transverse location of the primary interaction. This paper presents new methods of track reconstruction, measurements of strip-level detection efficiencies, cross-checks of the LHC beam optics, and detector alignment techniques, along with their application in the selection of signal collision events. The track reconstruction is performed by exploiting hit cluster information through a novel method using a common polygonal area in the intercept-slope plane. The technique is applied in the relative alignment of detector layers with $$\mu$$m precision. A tag-and-probe method is used to extract strip-level detection efficiencies. The alignment of the Roman pot system is performed through time-dependent adjustments, resulting in a position accuracy of 3 $$\mu$$m in the horizontal and 60 $$\mu$$m in the vertical directions. The goal is to provide an optimal reconstruction tool for central exclusive physics analyses based on the high-$$\beta^*$$ data-taking period at $$\sqrt{s}$$ = 13 TeV in 2018.

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.

A search is presented for rare decays of the Z and Higgs bosons to a photon and a J/$$\psi$$ or a $$\psi$$(2S) meson, with the charmonium state subsequentially decaying to a pair of muons. The data set corresponds to an integrated luminosity of 123 fb$$^{-1}$$ of proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector at the LHC. No evidence for branching fractions of these rare decay channels larger than predicted in the standard model is observed. Upper limits at 95% confidence level are set: $$\mathcal{B}$$(H $$\to$$ J/$$\psi \gamma$$) $$\lt$$ 2.6 $$\times$$ 10$$^{-4}$$, $$\mathcal{B}$$(H$$\to$$ $$\psi$$(2S)$$\gamma$$) $$\lt$$ 9.9 $$\times$$ 10$$^{-4}$$, $$\mathcal{B}$$(Z$$\to$$ J/$$\psi$$$$\gamma$$) $$\lt$$ 0.6 $$\times$$ 10$$^{-6}$$, and $$\mathcal{B}$$(Z$$\to$$$$\psi$$(2S)$$\gamma$$) $$\lt$$ 1.3 $$\times$$ 10$$^{-6}$$. The ratio of the Higgs boson coupling modifiers $$\kappa_\mathrm{c}/\kappa_\gamma$$ is constrained to be in the interval ($$-$$157, $$+$$199) at 95% confidence level. Assuming $$\kappa_\gamma=1$$, this interval becomes ($$-$$166, $$+$$208).

A full set of optimized observables is measured in an angular analysis of the decay B$^0$$$$\to$$ K$^*$(892)$$^0\mu^+\mu^-$$ using a sample of proton-proton collisions at $$\sqrt{s}$$ = 13 TeV, collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 140 fb$$^{-1}$$. The analysis is performed in six bins of the squared invariant mass of the dimuon system, $q^2$, over the range 1.1 $$\lt$$$$q^2$$$$\lt$$ 16 GeV$^2$. The results are among the most precise experimental measurements of the angular observables for this decay and are compared to a variety of predictions based on the standard model.