357 Search Results

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 Higgsmore » 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.[graphic not available: see fulltext]« less

The ratio between the B$$_\mathrm{c}^+$$$$\to$$ J/$$ψ$$$τ^+ν_τ$$ and B$$_\mathrm{c}^+$$$$\to$$ J/$$ψ$$$μ^+ν_μ$$ branching fractions is measured using a data sample of proton-proton collisions collected by CMS at a center-of-mass energy of 13 TeV in the years 2016$$-$$2018 and corresponding to an integrated luminosity of 138 fb$$^{-1}$$. The J$/ψ$ meson is identified through its J$/ψ$$$$\to$$$$μ^+μ^-$ decay and the tau lepton is reconstructed in the hadronic three-prong final state. The measured ratio of branching fractions in this tau decay mode, $$\mathcal{R}^\text{had}_{\mathrm{J}/ψ}$$ = 1.04 $$_{-0.44}^{+0.50}$$, is combined with the previous analysis based on the $τ^+$$$$\to$$$$μ^+ν_μ\barν_τ$$ leptonic decay channel, leading to $$\mathcal{R}_{\mathrm{J}/ψ}$$ = 0.49 $$\pm$$ 0.26. Asmore » this result is consistent with the standard model prediction of 0.258 $$\pm$$ 0.004, no evidence of lepton flavor universality violation is found.« less

Differential top quark pair production cross sections are measured in the dilepton final states e$$^{+}$$e$$^{−}$$, μ$$^{+}$$μ$$^{−}$$, and e$$^{±}$$μ$$^{∓}$$, as a function of kinematic variables of the two-neutrino system: the transverse momentum $$ {p}_{\textrm{T}}^{\nu \nu} $$ of the dineutrino system, the minimum distance in azimuthal angle between $$ {\overrightarrow{p}}_{\textrm{T}}^{\nu \nu} $$ and leptons, and in two dimensions in bins of both observables. The measurements are performed using CERN LHC proton-proton collisions at $$ \sqrt{s}=13 $$ TeV, recorded by the CMS detector between 2016 and 2018, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. The measured cross sections are unfolded to themore » particle level using an unregularized least squares method. Results are compared with predictions by the standard model of particle physics, and found to be in agreement with theoretical calculations as well as Monte Carlo simulations.[graphic not available: see fulltext]« less

The results of a search for the production of two scalar bosons in final states with two photons and two tau leptons are presented. The search considers both nonresonant production of a Higgs boson pair, HH, and resonant production via a new boson X which decays either to HH or to H and a new scalar Y. The analysis uses up to 138 fb$$^{−1}$$ of proton-proton collision data, recorded between 2016 and 2018 by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV. No evidence for signal is found in the data. For the nonresonant production,more » the observed (expected) upper limit at 95% confidence level (CL) on the HH production cross section is set at 930 (740) fb, corresponding to 33 (26) times the standard model prediction. At 95% CL, HH production is observed (expected) to be excluded for values of κ$$_{λ}$$ outside the range between −12 (−9.4) and 17 (15). Observed (expected) upper limits at 95% CL for the X → HH cross section are found to be within 160 to 2200 (200 to 1800) fb, depending on the mass of X. In the X → Y(ττ)H(γγ) search, the observed (expected) upper limits on the product of the production cross section and decay branching fractions vary between 0.059–1.2 fb (0.087–0.68 fb). For the X → Y(γγ)H(ττ) search the observed (expected) upper limits on the product of the production cross section and Y → γγ branching fraction vary between 0.69–15 fb (0.73–8.3 fb) in the low Y mass search, tightening constraints on the next-to-minimal supersymmetric standard model, and between 0.64–10 fb (0.70–7.6 fb) in the high Y mass search.[graphic not available: see fulltext]« less

A measurement of the angular structure of inclusive jets and those containing a prompt D$$^{0}$$ meson in proton-proton collisions at the LHC at a center-of-mass energy of 5.02 TeV is presented. The data corresponding to an integrated luminosity of 301 pb$$^{−1}$$ were collected by the CMS experiment in 2017. Two jet grooming algorithms, late-k$$_{T}$$ and soft drop, are used to study the intrajet radiation pattern using iterative Cambridge-Aachen declustering. The splitting-angle distributions of jets with transverse momentum (p$$_{T}$$) of around 100 GeV, obtained with these two algorithms, show that there is a shift of the distribution for jets containing amore » prompt D$$^{0}$$ meson with respect to inclusive jets. The suppression of emissions at small angles observed in the late-k$$_{T}$$ grooming approach is consistent with the dead-cone effect, whereas the similar suppression for splittings selected with the soft-drop algorithm appears to be induced by gluon splitting to charm quark-antiquark pairs at large angles. The measured distributions are corrected to the particle level and can be used to constrain model predictions for the substructure of high-p$$_{T}$$ charm quark jets.[graphic not available: see fulltext]« 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 measurement of the substructure of bottom quark jets (b jets) in proton-proton (pp) collisions is presented. The measurement uses data collected in pp collisions at $$\sqrt{s}=5.02$$ TeV, with a low number of simultaneous interactions per bunch crossing, recorded by the CMS experiment in 2017, corresponding to an integrated luminosity of 301 pb⁻¹. An algorithm to identify and cluster the charged decay daughters of b hadrons is developed for this analysis, which facilitates the exposure of the gluon radiation pattern of b jets using iterative Cambridge-Aachen declustering. The soft-drop-groomed jet radius, R_g, and momentum balance, z_g, of b quark jetsmore » are presented. These observables can be used to test perturbative quantum chromodynamics predictions that account for mass effects. Because the b hadron is partially reconstructed from its charged decay daughters, only charged particles are used for the jet substructure studies. In addition, a jet fragmentation function, z_b,ch, is measured, which is defined as the distribution of the ratio of the transverse momentum (p_T) of the partially reconstructed b hadron with respect to the charged-particle component of the jet p_T. The substructure variable distributions are unfolded to the charged-particle level. The b jet substructure is compared to the substructure of jets in an inclusive jet sample that is dominated by light-quark and gluon jets in order to assess the role of the b quark mass. A strong suppression of emissions at small R_g values is observed for b jets when compared to inclusive jets, consistent with the dead-cone effect. The measurement is also compared with theoretical predictions from Monte Carlo event generators. This is the first substructure measurement of b jets that clusters together the b hadron decay daughters independent of the b hadron species and decay channel.« 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