A measurement of the inclusive cross section of top quark pair production in association with a Z boson using proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC is performed. The data sample corresponds to an integrated luminosity of 77.5 fb$^{-1}$, collected by the CMS experiment during 2016 and 2017. The measurement is performed using final states containing three or four charged leptons (electrons or muons), and the Z boson is detected through its decay to an oppositely charged lepton pair. The production cross section is measured to be $\sigma(\mathrm{t\bar{t}Z})$ $=$ 0.95 $\pm$ 0.05 (stat) $\pm$ 0.06 (syst) pb. For the first time, differential cross sections are measured as functions of the transverse momentum of the Z boson and the angular distribution of the negatively charged lepton from the Z boson decay. The most stringent direct limits to date on the anomalous couplings of the top quark to the Z boson are presented, including constraints on the Wilson coefficients in the framework of the standard model effective field theory.
Measured absolute differential tt̄Z production cross section in the full phase space as a function of the transverse momentum of the Z boson, compared to the predictions obtained with the MadGraph5_aMC@NLO MC simulation, and to the theory prediction at NLO+NNLL accuracy (1905.07815). The distribution $Δσ$ is integrated over the bin, and $\mathrm{d}σ/\mathrm{d}p_{\mathrm{T}}(\mathrm{Z})$ is additionally divided by the bin width. The last bin includes the overflow contribution, but a finite bin width is used for the normalization.
Measured absolute differential tt̄Z production cross section in the full phase space as a function of the transverse momentum of the Z boson, compared to the predictions obtained with the MadGraph5_aMC@NLO MC simulation, and to the theory prediction at NLO+NNLL accuracy (1905.07815). The distribution $Δσ$ is integrated over the bin, and $\mathrm{d}σ/\mathrm{d}p_{\mathrm{T}}(\mathrm{Z})$ is additionally divided by the bin width. The last bin includes the overflow contribution, but a finite bin width is used for the normalization.
Measured normalized differential tt̄Z production cross section in the full phase space as a function of the transverse momentum of the Z boson, compared to the predictions obtained with the MadGraph5_aMC@NLO MC simulation, and to the theory prediction at NLO+NNLL accuracy (1905.07815). The distribution $1/σ\,Δσ$ is integrated over the bin, and $1/σ\,\mathrm{d}σ/\mathrm{d}p_{\mathrm{T}}(\mathrm{Z})$ is additionally divided by the bin width. The last bin includes the overflow contribution, but a finite bin width is used for the normalization.
A measurement of inclusive four-jet production in proton-proton collisions at a center-of-mass energy of 13\TeV is presented. The transverse momenta of jets within $\lvert\eta\rvert \lt$ 4.7 reach down to 35, 30, 25, and 20 GeV for the first-, second-, third-, and fourth-leading jet, respectively. Differential cross sections are measured as functions of the jet transverse momentum, jet pseudorapidity, and several other observables that describe the angular correlations between the jets. The measured distributions show sensitivity to different aspects of the underlying event, parton shower, and matrix element calculations. In particular, the interplay between angular correlations caused by parton shower and double-parton scattering contributions is shown to be important. The double-parton scattering contribution is extracted by means of a template fit to the data, using distributions for single-parton scattering obtained from Monte Carlo event generators and a double-parton scattering distribution constructed from inclusive single-jet events in data. The effective double-parton scattering cross section is calculated and discussed in view of previous measurements and of its dependence on the models used to describe the single-parton scattering background.
Comparison of the pT spectrum for the leading jet from data to different PYTHIA8 (P8),HERWIG++ (H++),and HERWIG7 (H7) tunes.
Comparison of the pT spectrum for the sub-leading from data to different PYTHIA8 (P8),HERWIG++ (H++),and HERWIG7 (H7) tunes.
Comparison of the pT spectrum for the third-leading from data to different PYTHIA8 (P8),HERWIG++ (H++),and HERWIG7 (H7) tunes.
Central exclusive and semiexclusive production of $\pi^+\pi^-$ pairs is measured with the CMS detector in proton-proton collisions at the LHC at center-of-mass energies of 5.02 and 13 TeV. The theoretical description of these nonperturbative processes, which have not yet been measured in detail at the LHC, poses a significant challenge to models. The two pions are measured and identified in the CMS silicon tracker based on specific energy loss, whereas the absence of other particles is ensured by calorimeter information. The total and differential cross sections of exclusive and semiexclusive central $\pi^+\pi^-$ production are measured as functions of invariant mass, transverse momentum, and rapidity of the $\pi^+\pi^-$ system in the fiducial region defined as transverse momentum $p_\mathrm{T}(\pi)$ $>$ 0.2 GeV and pseudorapidity $|\eta(\pi)|$ $<$ 2.4. The production cross sections for the four resonant channels f$_0(500)$, $\rho^0(770)$, f$_0(980)$, and f$_2(1270)$ are extracted using a simple model. These results represent the first measurement of this process at the LHC collision energies of 5.02 and 13 TeV.
Differential cross section as a function of the invariant mass of the pion pair at 5.02 TeV, compared with generator-level simulations.
Differential cross section as a function of the invariant mass of the pion pair at 13 TeV, compared with generator-level simulations.
Differential cross section as a function of the transverse momentum of the pion pair at 5.02 TeV, compared with generator-level simulations.
A measurement is presented of the production of Z bosons that decay into two electrons or muons in association with jets, in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data were recorded by the CMS Collaboration at the LHC with an integrated luminosity of 35.9 fb$^{-1}$. The differential cross sections are measured as a function of the transverse momentum ($p_\mathrm{T}$) of the Z boson and the transverse momentum and rapidities of the five jets with largest $p_\mathrm{T}$. The jet multiplicity distribution is measured for up to eight jets. The hadronic activity in the events is estimated using the scalar sum of the $p_\mathrm{T}$ of all the jets. All measurements are unfolded to the stable particle-level and compared with predictions from various Monte Carlo event generators, as well as with expectations at leading and next-to-leading orders in perturbative quantum chromodynamics.
Measured cross section as a function of exclusive jet multiplicity, $N_{\text{jets}}$, and breakdown of the relative uncertainty.
Bin-to-bin correlation in the measured cross section as a function of exclusive jet multiplicity, $N_{\text{jets}}$.
Measured cross section as a function of the rapidity absolute value of the first jet, $|y(\text{j}_1)|$, and breakdown of the relative uncertainty.
Double-parton scattering is investigated using events with a Z boson and jets. The Z boson is reconstructed using only the dimuon channel. The measurements are performed with proton-proton collision data recorded by the CMS experiment at the LHC at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$ collected in the year 2016. Differential cross sections of Z + $\geq$ 1 jet and Z + $\geq$ 2 jets are measured with transverse momentum of the jets above 20 GeV and pseudorapidity $|\eta|$$\lt$ 2.4. Several distributions with sensitivity to double-parton scattering effects are measured as functions of the angle and the transverse momentum imbalance between the Z boson and the jets. The measured distributions are compared with predictions from several event generators with different hadronization models and different parameter settings for multiparton interactions. The measured distributions show a dependence on the hadronization and multiparton interaction simulation parameters, and are important input for future improvements of the simulations.
Differential cross sections as function of Delta Phi between Z boson and the leading jet for Z+ ≥ 1 jet events.
Differential cross sections as function of transverse momentum imbalance between Z boson and the leading jet for Z+ ≥ 1 jet events.
Differential cross sections as function of Delta Phi between Z boson and dijet for Z+ ≥ 2 jets events.
The inclusive jet cross section is measured as a function of jet transverse momentum $p_\mathrm{T}$ and rapidity $y$. The measurement is performed using proton-proton collision data at $\sqrt{s}$ = 5.02 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 27.4 pb$^{-1}$. The jets are reconstructed with the anti-$k_\mathrm{T}$ algorithm using a distance parameter of $R$ = 0.4, within the rapidity interval $\lvert y\rvert$$\lt$ 2, and across the kinematic range 0.06 $\lt$$p_\mathrm{T}$$\lt$ 1 TeV. The jet cross section is unfolded from detector to particle level using the determined jet response and resolution. The results are compared to predictions of perturbative quantum chromodynamics, calculated at both next-to-leading order and next-to-next-to-leading order. The predictions are corrected for nonperturbative effects, and presented for a variety of parton distribution functions and choices of the renormalization/factorization scales and the strong coupling $\alpha_\mathrm{S}$.
The JEC, JER, and total systematic uncertainties in unfolded cross sections as functions of transverse momentum, for |y|<0.5. The total systematic uncertainty includes also the luminosity, jet identification and trigger efficiency uncertainties.
The JEC, JER, and total systematic uncertainties in unfolded cross sections as functions of transverse momentum, for 0.5<|y|<1. The total systematic uncertainty includes also the luminosity, jet identification and trigger efficiency uncertainties.
The JEC, JER, and total systematic uncertainties in unfolded cross sections as functions of transverse momentum, for 1<|y|<1.5. The total systematic uncertainty includes also the luminosity, jet identification and trigger efficiency uncertainties.
The strange quark content of the proton is probed through the measurement of the production cross section for a W boson and a charm (c) quark in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis uses a data sample corresponding to a total integrated luminosity of 138 fb$^{-1}$ collected with the CMS detector at the LHC. The W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm jets are tagged using the presence of a muon or a secondary vertex inside the jet. The W+c production cross section and the cross section ratio $R^\pm_\text{c}$ = $\sigma$(W$^+$+$\bar{\text{c}}$) / $\sigma$(W$^-$+$\text{c}$) are measured inclusively and differentially as functions of the transverse momentum and the pseudorapidity of the lepton originating from the W boson decay. The precision of the measurements is improved with respect to previous studies, reaching 1% in $R^\pm_\text{c}$. The precision of the measurements is improved with respect to previous studies, reaching 1% in $R^\pm_\text{c}$ = 0.950 $\pm$ 0.005 (stat) $\pm$ 0.010 (syst). The measurements are compared with theoretical predictions up to next-to-next-to-leading order in perturbative quantum chromodynamics.
Particle level efficiency*acceptance correction factors and cross section measurements for the four channels (W decay to muon or electron and charm identification via muon or secondary vertex inside a jet). The combined measurement is shown in the last row.
Parton level efficiency*acceptance correction factors and cross section measurements for the four channels (W decay to muon or electron and charm identification via muon or secondary vertex inside a jet). The combined measurement is shown in the last row.
Inclusive cross section predictions at QCD NLO accuracy from MCFM using different PDF sets
Diboson production in association with jets is studied in the fully leptonic final states, pp $\to$ (Z$\gamma^*$)(Z/$\gamma^*$)+jets $\to$ 2$\ell$2$\ell'$+jets, ($\ell,\ell'$ = e or $\mu$) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 138 fb$^{-1}$ collected with the CMS detector at the LHC. Differential distributions and normalized differential cross sections are measured as a function of jet multiplicity, transverse momentum $p_\mathrm{T}$, pseudorapidity $\eta$, invariant mass and $\Delta\eta$ of the highest-$p_\mathrm{T}$ and second-highest-$p_\mathrm{T}$ jets, and as a function of invariant mass of the four-lepton system for events with various jet multiplicities. These differential cross sections are compared with theoretical predictions that mostly agree with the experimental data. However, in a few regions we observe discrepancies between the predicted and measured values. Further improvement of the predictions is required to describe the ZZ+jets production in the whole phase space.
Differential cross sections normalized to the fiducial cross section as a function of the invariant mass of the four-lepton system, in the on-shell ZZ region
Differential cross sections normalized to the fiducial cross section as a function of the number of jets with $p_T > 30$ GeV
Differential cross sections normalized to the fiducial cross section as a function of the $p_T$ of the highest-$p_T$ jet
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