63 Search Results

A search for a Higgs boson produced in association with a W or Z boson and decaying via a soft unclustered energy pattern (SUEP) is presented. The analysis is based on proton-proton collision data corresponding to an integrated luminosity of 138fb−1 collected between 2016 and 2018 at the LHC. Final states with a leptonic W or Z boson decay associated with a high multiplicity of low-momentum charged particles are explored for the first time. The results show no significant excess over the standard model background expectation. Limits are set on the production cross section of a Higgs boson that decaysmore » to a SUEP, for a range of parameters of the SUEP model. Material is provided to facilitate further interpretation of the results.« less

A search for the pair production of heavy spin- $1/2$ or spin- $3/2$ resonances ( $t^{*}$ ) in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ is presented. Data collected with the CMS detector at the CERN LHC from 2016 to 2018 corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ are used. The analysis targets benchmark signal scenarios where one $t^{*}$ decays into a top quark ( $t$ ) and a photon ( $\gamma$ ), and the other into a $t$ quarkmore » and a gluon ( $g$ ), i.e., $pp\to t^{*}\overline{t^{*}}\to tt\gamma g$ . All-hadronic final states from the $t$ pair decay chain are selected using jet substructure techniques. The signal is probed as a function of the $t^{*}$ candidate mass, which is reconstructed using the photon and a top quark candidate jet. No significant deviation from the background-only hypothesis is found. Observed (expected) upper limits on the signal cross section at 95% confidence level are set, excluding masses of spin- $1/2$ $t^{*}$ particles below 930 (930) GeV and spin- $3/2$ $t^{*}$ particles below 1330 (1390) GeV. This analysis marks the first search for heavy resonances in the $t\overline{t}\gamma g$ channel. Exploiting the high-energy photon to reduce the backgrounds, this search achieves sensitivity competitive with $pp\to t^{*}\overline{t^{*}}\to t\overline{t}gg$ searches for spin- $1/2$ $t^{*}$ despite the small expected $t^{*}\to t\gamma$ branching fraction.« less

A novel anomaly detection algorithm is presented. The Wasserstein normalized autoencoder (WNAE) is a normalized probabilistic model that minimizes the Wasserstein distance between the learned probability distribution—a Boltzmann distribution where the energy is the reconstruction error of the autoencoder (AE)—and the distribution of the training data. This algorithm has been developed and applied to the identification of semivisible jets—conical sprays of visible standard model (SM) particles and invisible dark matter states—with the CMS experiment at the CERN LHC. Trained on jets of particles from simulated SM processes, the WNAE is shown to learn the probability distribution of the input datamore » in a fully unsupervised fashion, such that it effectively identifies new physics jets as anomalies. The model exhibits stable, convergent training and recovers strong classification performance for a wide range of signals against the selected background process, for which a standard AE fails because of outlier reconstruction. In addition, the model improves upon standard normalized autoencoders while remaining fully agnostic to the signal. The WNAE directly tackles the problem of outlier reconstruction, a common failure mode of autoencoders in anomaly detection tasks.« less

A pioneering machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27$$\,$$000 tagged B$$^0_\mathrm{s}$$$$\to$$ J/$$\psi\, \phi$$(1020) decays from pp collisions at $$\sqrt{s} =$$ 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb$$^{-1}$$. A time- and flavor-dependent angular analysis of the $$\mu^+\mu^-$$K$$^+$$K$$^-$ final state is used to measure parameters of the $$\mathrm{B}^0_\mathrm{s}$$-$$\overline{\mathrm{B}}^0_\mathrm{s}$$ system. The weak phase is measured to be $$\phi_\mathrm{s}$$ = $$-$$73 $$\pm$$ 23 (stat) $$\pm$$ 7 (syst) mrad, which, combined with a $$\sqrt{s}$$ = 8 TeV CMS result, gives $$\phi_\mathrm{s}$$ = $$-$$74 $$\pm$$ 23 mrad. Thismore » value differs from zero by 3.2 standard deviations, providing evidence for $CP$ violation in B$$^0_\mathrm{s}$$$$\to$$ J/$$\psi\,\phi$$(1020) decays. All measured physics parameters are found to agree with standard model predictions where available.« less

A search for a pair of light pseudoscalar bosons (a₁) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a₁ decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a1 boson mass probed in this study ranges from 4 to 15 GeV. The data sample was recorded by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponds to an integrated luminosity of 138 fb⁻¹. No excess above standard modelmore » (SM) expectations is observed. The study combines the 4τ and 2μ2τ channels to set upper limits at 95% confidence level (CL) on the product of the Higgs boson production cross section and the branching fraction to the 4τ final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a₁ boson is assumed to have Yukawa-like couplings to fermions, with coupling strengths proportional to the respective fermion masses. The observed (expected) upper limits range between 0.007 (0.011) and 0.079 (0.066) across the mass range considered. The results are also interpreted in the context of models with two Higgs doublets and an additional complex singlet field (2HD+S). The tightest constraints are obtained for the Type III 2HD+S model. In this case, assuming the Higgs boson production cross section equals the SM prediction, values of the branching ratio for the Higgs boson decay into a pair of a1 bosons exceeding 16% are excluded at 95% CL for a1 boson masses between 5 and 15 GeV and tan β > 2, with the exception of scenarios in which the a1 boson mixes with charm or bottom quark-antiquark bound states.« less

Precision measurements of Higgs boson differential production cross sections are a key tool to probe the properties of the Higgs boson and test the standard model. New physics can affect both Higgs boson production and decay, leading to deviations from the distributions that are expected in the standard model. In this paper, combined measurements of differential spectra in a fiducial region matching the experimental selections are performed, based on analyses of four Higgs boson decay channels (γγ, ZZ$$^{(*)}$$, WW$$^{(*)}$$, and ττ) using proton-proton collision data recorded with the CMS detector at $$ \sqrt{s}=13 $$ TeV, corresponding to an integrated luminositymore » of 138 fb$$^{−1}$$. The differential measurements are extrapolated to the full phase space and combined to provide the differential spectra. A measurement of the total Higgs boson production cross section is also performed using the γγ and ZZ decay channels, with a result of $$ {53.4}_{-2.9}^{+2.9}{\left(\textrm{stat}\right)}_{-1.8}^{+1.9}\left(\textrm{syst}\right) $$ pb, consistent with the standard model prediction of 55.6 ± 2.5 pb. The fiducial measurements are used to compute limits on Higgs boson couplings using the κ-framework and the SM effective field theory.[graphic not available: see fulltext]« less

In the standard model of particle physics, the masses of the W and Z bosons, the carriers of the weak interaction, are uniquely related. A precise determination of their masses is important because quantum loops of heavy, undiscovered particles could modify this relationship. Although the Z mass is known to the remarkable precision of 22 parts per million (2.0 MeV), the W mass is known much less precisely. A global fit to measured electroweak observables predicts the W mass with 6 MeV uncertainty [1$$-$$3]. Reaching a comparable experimental precision would be a sensitive and fundamental test of the standard model,more » made even more urgent by a recent challenge to the global fit prediction by a measurement from the CDF Collaboration at the Fermilab Tevatron collider [4]. Here we report the measurement of the W mass by the CMS Collaboration at the CERN LHC, based on a large data sample of $$W \to \mu \nu$$ events collected in 2016 at the proton-proton collision energy of 13 TeV. The measurement exploits a high-granularity maximum likelihood fit to the kinematic properties of muons produced in W decays. By combining an accurate determination of experimental effects with marked in situ constraints of theoretical inputs, we reach a precise measurement of the W mass, of 80 360.2 $$\pm$$ 9.9 MeV, in agreement with the standard model prediction.« less

The first observation of coherent 𝜙⁡(1020) meson photoproduction off heavy nuclei is presented using ultraperipheral lead-lead collisions at a center-of-mass energy per nucleon pair of 5.36 TeV. The data were collected by the CMS experiment and correspond to an integrated luminosity of 1.62 μ⁢𝑏⁻¹. The 𝜙⁡(1020) meson signals are reconstructed via the 𝐾⁺⁢𝐾⁻ decay channel. The production cross section is presented as a function of the 𝜙⁡(1020) meson rapidity in the range 0.3 < |𝑦| < 1.0, probing gluons that carry a fraction of the nucleon momentum (𝑥) around 10⁻⁴. The observed cross section exhibits little dependence on rapidity andmore » is significantly suppressed, by a factor of ∼5, compared to a baseline model that treats a nucleus as a collection of free nucleons. Theoretical models that incorporate the nuclear shadowing effect generally provide a better description of the 𝜙⁡(1020) data than those incorporating gluon saturation. This study establishes a powerful new tool for exploring nuclear effects and nuclear gluonic structure in the small-𝑥 regime at a unique energy scale bridging the perturbative and nonperturbative quantum chromodynamics domains.« less

A tau lepton identification algorithm,DeepTau, based on convolutional neural network techniques, has been developed in the CMS experiment to discriminate reconstructed hadronic decays of tau leptons (τ_h) from quark or gluon jets and electrons and muons that are misreconstructed as τ_h candidates. The latest version of this algorithm, v2.5, includes domain adaptation by backpropagation, a technique that reduces discrepancies between collision data and simulation in the region with the highest purity of genuine τh candidates. Additionally, a refined training workflow improves classification performance with respect to the previous version of the algorithm, with a reduction of 30–50% in the probabilitymore » for quark and gluon jets to be misidentified as τ_h candidates for given reconstruction and identification efficiencies. This paper presents the novel improvements introduced in theDeepTau algorithm and evaluates its performance in LHC proton-proton collision data at √(s) = 13 and 13.6 TeV collected in 2018 and 2022 with integrated luminosities of 60 and 35 fb^-1, respectively. Techniques to calibrate the performance of the τ_h identification algorithm in simulation with respect to its measured performance in real data are presented, together with a subset of results among those measured for use in CMS physics analyses.« less

A search for t-channel exchange of leptoquarks (LQs) is performed in dimuon and dielectron spectra using proton-proton collision data collected at $$\sqrt{s}=13$$ TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 138 fb⁻¹. Eight scenarios are considered, in which up or down quarks couple to muons or electrons via a scalar or vector LQ exchange, for dilepton invariant masses above 500 GeV. The LQ masses are probed up to 5 TeV, beyond a regime probed by previous pair-production and single-production searches. The differential distributions of dilepton events are fit to templates thatmore » model the nonresonant LQ exchange and various standard model background processes. Limits are set on LQ-fermion coupling strengths for scalar and vector LQ masses in the 1–5 TeV range at 95% confidence level, establishing stringent limits on first- and second-generation LQs.« less