A search for a pair of light pseudoscalar bosons (a$_1$) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a$_1$ decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a$_1$ 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 model (SM) expectations is observed. The study combines the 4$τ$ and 2$μ$2$τ$ 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 4$τ$ final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a$_1$ 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 a$_1$ bosons exceeding 16% are excluded at 95% CL for a$_1$ boson masses between 5 and 15 GeV and $\tanβ$ $\gt$ 2, with the exception of scenarios in which the a$_1$ boson mixes with charm or bottom quark-antiquark bound states.
The observed and expected upper limits at 95% confidence level on the product of the signal cross section and the branching fraction $\sigma (\mathrm{pp} \to \mathrm{H}+\text{X}) {\mathcal{B}} (\mathrm{H} \to \mathrm{a}_1\,\mathrm{a}_1) {\mathcal{B}}^{2} (\mathrm{a}_1 \to \tau \tau)$, relative to the inclusive Higgs boson production cross section $\sigma_\text{SM}$ predicted in the SM. The green and yellow bands indicate the regions containing 68% and 95% of the distribution of limits expected under the background-only hypothesis.
The observed and expected upper limits at 95% CLs on $\sigma (\mathrm{pp} \to \mathrm{H}+\text{X}) {\mathcal{B}} (\mathrm{H} \to \mathrm{a}_1\,\mathrm{a}_1)$, relative to $\sigma_\text{SM}$, as a function of $m_{\mathrm{a}_1}$ for Type I 2HD+S model ($\tan\beta$ independent).
The observed and expected upper limits at 95% CLs on $\sigma (\mathrm{pp} \to \mathrm{H}+\text{X}) {\mathcal{B}} (\mathrm{H} \to \mathrm{a}_1\,\mathrm{a}_1)$, relative to $\sigma_\text{SM}$, as a function of $m_{\mathrm{a}_1}$ for Type II 2HD+S model, $\tan\beta = 5$.
A measurement of the angular structure of jets containing a prompt D$^0$ meson and of inclusive jets 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-$k_\mathrm{T}$ 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 ($p_\mathrm{T}$) of around 100 GeV, obtained with these two algorithms, show that there is a shift of the distribution for jets containing a prompt D$^0$ meson with respect to inclusive jets. The shift observed in the late-$k_\mathrm{T}$ grooming approach is consistent with the dead-cone effect, whereas the shift for splittings selected with the soft-drop algorithm appears to be dominated by gluon splitting to charm quark-antiquark pairs. The measured distributions are corrected to the particle level and can be used to constrain model predictions for the substructure of high-$p_\mathrm{T}$ charm quark jets.
The unfolded late-$k_{T}$ angular distribution for prompt $D^{0}$ jets.
The unfolded late-$k_{T}$ angular distribution for inclusive jets.
The unfolded SD angular distribution for prompt $D^{0}$ jets.
The first measurement of pseudorapidity and azimuthal angle distributions relative to the momentum vector of a Z boson for low transverse momentum ($p_\mathrm{T}$) charged hadrons in lead-lead (PbPb) collisions is presented. By studying the hadrons produced in an event with a high-$p_\mathrm{T}$ Z boson (40 $\lt$$p_\mathrm{T}$$\lt$ 350 GeV), the analysis probes how the quark-gluon plasma (QGP) medium created in these collisions affects the parton recoiling opposite to the Z boson. Utilizing PbPb data at a nucleon-nucleon center-of-mass energy $\sqrt{s_{_\mathrm{NN}}}$ = 5.02 TeV from 2018 with an integrated luminosity of 1.67 nb$^{-1}$ and proton-proton (pp) data at the same energy from 2017 with 301 pb$^{-1}$, the distributions are examined in bins of charged-hadron $p_\mathrm{T}$. A significant modification of the distributions for charged hadrons in the range 1$\lt$$p_\mathrm{T}$$\lt$ 2 GeV in PbPb collisions is observed when compared to reference measurements from pp collisions. The data provide new information about the correlation between hard and soft particles in heavy ion collisions, which can be used to test predictions of various jet quenching models. The results are consistent with expectations of a hydrodynamic wake created when the QGP is depleted of energy by the parton propagating through it. Based on comparisons of PbPb data with pp references and predictions from theoretical models, this Letter presents the first evidence of medium-recoil and medium-hole effects caused by a hard probe.
The $\Delta\phi_{ch,Z}$ spectra for events with Z boson $p_{T}^Z > 40$ GeV and charged-hadrons with $1 <p_T < 2$ GeV in pp collisions.
The $\Delta\phi_{ch,Z}$ spectra for events with Z boson $p_{T}^Z > 40$ GeV and charged-hadrons with $2 <p_T < 4$ GeV in pp collisions.
The $\Delta\phi_{ch,Z}$ spectra for events with Z boson $p_{T}^Z > 40$ GeV and charged-hadrons with $4 <p_T < 10$ GeV in pp collisions.
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, 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 XHH cross section are found to be within 160 to 2200 (200 to 1800) fb, depending on the mass of X. In the X $\to$ Y($γγ$)H($ττ$) 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 $\to$ Y($γγ$)H($ττ$) search the observed (expected) upper limits on the product of the production cross section and Y $to$ $γγ$ 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.
Observed and expected 95% CL upper limits on the nonresonant $\mathrm{HH}$ production cross section, $\sigma(\mathrm{pp} \to \mathrm{HH})$, as a function of the Higgs boson self-coupling strength modifier $\kappa_\lambda$. All Higgs boson couplings other than $\lambda$ are assumed to have the values predicted in the SM.
Observed and expected 95% CL upper limits on the nonresonant $\mathrm{HH}$ production cross section, $\sigma(\mathrm{pp} \to \mathrm{HH})$, for thirteen different BSM benchmark scenarios from [arXiv:1507.02245, arXiv:1806.05162] which consider different values of the couplings, $\kappa_\lambda$, $\kappa_t$, $c_{2g}$, $c_g$, and $c_2$ (defined in Table 1).
Observed and expected 95% CL upper limits on the cross section for the resonant production of a new spin-0 particle $\mathrm{X}^{(0)}$ which decays to Higgs boson pairs, $\sigma(\mathrm{pp} \to \mathrm{X}^{(0)} \to \mathrm{HH})$, given for different values of $m_\mathrm{X}$ in the range 260-1000 GeV.
A search for nonresonant new physics phenomena in high-mass dilepton events produced in association with b-tagged jets is performed using proton-proton collision data collected in 2016$-$2018 by the CMS experiment at the CERN LHC, at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis considers two effective field theory models with dimension-six operators; involving four-fermion contact interactions between two leptons ($\ell\ell$, electrons or muons) and b or s quarks (bb$\ell\ell$ and bs$\ell\ell$). Two lepton flavor combinations (ee and $μμ$) are required and events are classified as having 0, 1, and $\geq$2 b-tagged jets in the final state. No significant excess is observed over the standard model backgrounds. Upper limits are set on the production cross section of the new physics signals. These translate into lower limits on the energy scale $Λ$ of 6.9 to 9.0 TeV in the bb$\ell\ell$ model, depending on model parameters, and on the ratio of energy scale and effective coupling, $Λ/g_*$, of 2.0 to 2.6 TeV in the bs$\ell\ell$ model. The latter represent the most stringent limits on this model to date. Lepton flavor universality is also tested by comparing the dielectron and dimuon mass spectra for different b-tagged jet multiplicities. No significant deviation from the standard model expectation of unity is observed.
Signal efficiencies with Full Run 2 dimuon channel for different bbll signal scenarios
Signal efficiencies with Full Run 2 dimuon channel for different bbll (destructive interference) signal scenarios
Signal efficiencies with Full Run 2 dimuon channel in 1b final state for different bbll signal scenarios
Several new physics models including versions of supersymmetry (SUSY) characterized by $R$-parity violation (RPV) or with additional hidden sectors predict the production of events with top quarks, low missing transverse momentum, and many additional quarks or gluons. The results of a search for top squarks decaying to two top quarks and six additional light-flavor quarks or gluons are reported. The search employs a novel machine learning method for background estimation from control samples in data using decorrelated discriminators. The search is performed using events with 0, 1, or 2 electrons or muons in conjunction with at least six jets. No requirement is placed on the magnitude of the missing transverse momentum. The result is based on a sample of proton-proton collisions at $\sqrt{s}$ = 13 TeV corresponding to 138 fb$^{-1}$ of integrated luminosity collected with the CMS detector at the LHC in 2016$-$2018. The data are used to determine upper limits on the top squark pair production cross section in the frameworks of RPV and stealth SUSY. Models with top squark masses less than 700 (930) GeV are excluded at 95% confidence level for RPV (stealth) SUSY scenarios.
Cutflows and signal efficiencies for the RPV SUSY model in the $0\ell$ channel corresponding to two values of $m_{\tilde{t}}$.
Cutflows and signal efficiencies for the Stealth SYY SUSY model in the $0\ell$ channel corresponding to two values of $m_{\tilde{t}}$.
Cutflows and signal efficiencies for the RPV SUSY model in the $1\ell$ channel corresponding to two values of $m_{\tilde{t}}$.
A search for the rare decay D$^0$$\to$$\mu^+\mu^-$ is reported using proton-proton collision events at $\sqrt{s}$ = 13.6 TeV collected by the CMS detector in 2022$-$2023, corresponding to an integrated luminosity of 64.5 fb$^{-1}$. This is the first analysis to use a newly developed inclusive dimuon trigger, expanding the scope of the CMS flavor physics program. The search uses D$^0$ mesons obtained from D$^{*+}$$\to$ D$^0\pi^+$ decays. No significant excess is observed. A limit on the branching fraction of $\mathcal{B}$(D$^0$$\to$$\mu^+\mu^-$) $\lt$ 2.4 $\times$ 10$^{-9}$ at 95% confidence level is set. This is the most stringent upper limit set on any flavor changing neutral current decay in the charm sector.
Summary of branching fraction.
Summary of systematic uncertainties for the D->mumu branching fraction measurement with their corresponding contributions in the signal channel.
The distributions of the dipion invariant mass $m_{\pi\pi}$ for the normalization channel in data.
A search for dark matter particles produced in association with a Higgs boson decaying into a pair of $\tau$ leptons is performed using data collected in proton-proton collisions at a center-of-mass energy of 13 TeV with the CMS detector. The analysis is based on a data set corresponding to an integrated luminosity of 101 fb$^{-1}$ collected in 2017$-$2018. No significant excess over the expected standard model background is observed. This result is interpreted within the frameworks of the 2HDM+a and baryonic Z$'$ benchmark simplified models. The 2HDM+a model is a type-II two-Higgs-doublet model featuring a heavy pseudoscalar with an additional light pseudoscalar. Upper limits at 95% confidence level are set on the product of the production cross section and the branching fraction for each of these two simplified models. Heavy pseudoscalar boson masses between 400 and 700 GeV are excluded for a light pseudoscalar mass of 100 GeV. For the baryonic Z$'$ model, a statistical combination is made with an earlier search based on a data set of 36 fb$^{-1}$ collected in 2016. In this model, Z$'$ boson masses up to 1050 GeV are excluded for a dark matter particle mass of 1 GeV.
Distributions of the total transverse mass $M_{T}^{tot}$ in the SRs, comparing observed data with the SM prediction in the $e\tau_{h}$ final states in 2017 (upper left) after the simultaneous maximum likelihood fit. Representative signal distributions are shown for the 2HDM+a (dashed red curve) and baryonic Z' (dashed black curve) models. The data points are shown with their statistical uncertainties, and the last bin includes overflow. The ``Other MC'' background contribution includes events from ggh, VBF, Wh, Zh, and electroweak vector boson production. The uncertainty band accounts for all systematic and statistical sources of uncertainty, after the fit to the data.
Distributions of the total transverse mass $M_{T}^{tot}$ in the SRs, comparing observed data with the SM prediction in the $e\tau_{h}$ final states in 2018 (upper right) after the simultaneous maximum likelihood fit. Representative signal distributions are shown for the 2HDM+a (dashed red curve) and baryonic Z' (dashed black curve) models. The data points are shown with their statistical uncertainties, and the last bin includes overflow. The ``Other MC'' background contribution includes events from ggh, VBF, Wh, Zh, and electroweak vector boson production. The uncertainty band accounts for all systematic and statistical sources of uncertainty, after the fit to the data.
Distributions of the total transverse mass $M_{T}^{tot}$ in the SRs, comparing observed data with the SM prediction in the $\mu\tau_{h}$ final states in 2017 (center left) after the simultaneous maximum likelihood fit. Representative signal distributions are shown for the 2HDM+a (dashed red curve) and baryonic Z' (dashed black curve) models. The data points are shown with their statistical uncertainties, and the last bin includes overflow. The ``Other MC'' background contribution includes events from ggh, VBF, Wh, Zh, and electroweak vector boson production. The uncertainty band accounts for all systematic and statistical sources of uncertainty, after the fit to the data.
A measurement of event-shape variables is presented, using a data sample produced in a special run with approximately one inelastic proton-proton collision per bunch crossing. The data were collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 64 $\mu$b$^{-1}$. A number of observables related to the overall distribution of charged particles in the collisions are corrected for detector effects and compared with simulations. Inclusive event-shape distributions, as well as differential distributions of event shapes as functions of charged-particle multiplicity, are studied. None of the models investigated is able to satisfactorily describe the data. Moreover, there are significant features common amongst all generator setups studied, particularly showing data being more isotropic than any of the simulations. Multidimensional unfolded distributions are provided, along with their correlations.
The unfolded charged particle multiplicity distribution of inelastic proton-proton collisions with at least three charged particles with transverse momentum higher than 0.5 GeV and pseudorapidity between -2.4 and 2.4. The total area of the histogram is normalised to 1.
The unfolded charged particle invariant mass distribution of inelastic proton-proton collisions with at least three charged particles with transverse momentum higher than 0.5 GeV and pseudorapidity between -2.4 and 2.4. The total area of the histogram is normalised to 1.
The unfolded charged particle sphericity distribution of inelastic proton-proton collisions with at least three charged particles with transverse momentum higher than 0.5 GeV and pseudorapidity between -2.4 and 2.4. The total area of the histogram is normalised to 1.
A search is performed for dark matter (DM) produced in association with a single top quark or a pair of top quarks using the data collected with the CMS detector at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to 138 fb$^{-1}$ of integrated luminosity. An excess of events with a large imbalance of transverse momentum is searched for across 0, 1 and 2 lepton final states. Novel multivariate techniques are used to take advantage of the differences in kinematic properties between the two DM production mechanisms. No significant deviations with respect to the standard model predictions are observed. The results are interpreted considering a simplified model in which the mediator is either a scalar or pseudoscalar particle and couples to top quarks and to DM fermions. Axion-like particles that are coupled to top quarks and DM fermions are also considered. Expected exclusion limits of 410 and 380 GeV for scalar and pseudoscalar mediator masses, respectively, are set at the 95% confidence level. A DM particle mass of 1 GeV is assumed, with mediator couplings to fermions and DM particles set to unity. A small signal-like excess is observed in data, with the largest local significance observed to be 1.9 standard deviations for the 150 GeV pseudoscalar mediator hypothesis. Because of this excess, mediator masses are only excluded below 310 (320) GeV for the scalar (pseudoscalar) mediator. The results are also translated into model-independent 95% confidence level upper limits on the visible cross section of DM production in association with top quarks, ranging from 1 pb to 0.02 pb.
The post-fit $p_{\mathrm{T}}^{\text{miss}}$ distribution of the 1 b jet, 0 forward jet signal region in the all hadronic channel. A representative signal model distribution is shown for the scalar mediator interaction with $(m_{\chi},m_{\phi})=(1,100)$GeV and couplings set to unity. The grey dashed area in the upper panel represents the total uncertainty in all of the backgrounds and the chosen signal model, while in the lower panel it represents only the total uncertainty in the backgrounds.
The post-fit $p_{\mathrm{T}}^{\text{miss}}$ distribution of the 1 b jet, $\geq 1$ forward jet signal region in the all hadronic channel. A representative signal model distribution is shown for the scalar mediator interaction with $(m_{\chi},m_{\phi})=(1,100)$GeV and couplings set to unity. The grey dashed area in the upper panel represents the total uncertainty in all of the backgrounds and the chosen signal model, while in the lower panel it represents only the total uncertainty in the backgrounds.
The post-fit $p_{\mathrm{T}}^{\text{miss}}$ distribution of the $\geq 2$ b jet signal region in the all hadronic channel. A representative signal model distribution is shown for the scalar mediator interaction with $(m_{\chi},m_{\phi})=(1,100)$GeV and couplings set to unity. The grey dashed area in the upper panel represents the total uncertainty in all of the backgrounds and the chosen signal model, while in the lower panel it represents only the total uncertainty in the backgrounds.
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