Measurement of the Dependence of the Hadron Production Fraction Ratios f_{s}/f_{u} and f_{d}/f_{u} on B Meson Kinematic Variables in Proton-Proton Collisions at sqrt[s]=13 TeV.

The dependence of the ratio between the B_{s}^{0} and B^{+} hadron production fractions, f_{s}/f_{u}, on the transverse momentum (p_{T}) and rapidity of the B mesons is studied using the decay channels B_{s}^{0}→J/ψϕ and B^{+}→J/ψK^{+}. The analysis uses a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 61.6 fb^{-1}. The f_{s}/f_{u} ratio is observed to depend on the B p_{T} and to be consistent with becoming asymptotically constant at large p_{T}. No rapidity dependence is observed. The ratio of the B^{0} to B^{+} meson production fractions, f_{d}/f_{u}, is also measured, for the first time in proton-proton collisions, using the B^{0}→J/ψK^{*0} decay channel. The result is found to be within 1 standard deviation of unity and independent of p_{T} and rapidity, as expected from isospin invariance.

Observation of τ Lepton Pair Production in Ultraperipheral Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV.

We present an observation of photon-photon production of τ lepton pairs in ultraperipheral lead-lead collisions. The measurement is based on a data sample with an integrated luminosity of 404 µb^{-1} collected by the CMS experiment at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=5.02 TeV. The γγ→τ^{+}τ^{-} process is observed for τ^{+}τ^{-} events with a muon and three charged hadrons in the final state. The measured fiducial cross section is σ(γγ→τ^{+}τ^{-})=4.8±0.6(stat)±0.5(syst) µb, where the second (third) term corresponds to the statistical (systematic) uncertainty in σ(γγ→τ^{+}τ^{-}) in agreement with leading-order QED predictions. Using σ(γγ→τ^{+}τ^{-}), we estimate a model-dependent value of the anomalous magnetic moment of the τ lepton of a_{τ}=0.001_{-0.089}^{+0.055}.

A search for decays of the Higgs boson to invisible particles in events with a top-antitop quark pair or a vector boson in proton-proton collisions at s=13TeV.

A search for decays to invisible particles of Higgs bosons produced in association with a top-antitop quark pair or a vector boson, which both decay to a fully hadronic final state, has been performed using proton-proton collision data collected at s=13TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138fb-1. The 95% confidence level upper limit set on the branching fraction of the 125GeV Higgs boson to invisible particles, B(H→inv), is 0.54 (0.39 expected), assuming standard model production cross sections. The results of this analysis are combined with previous B(H→inv) searches carried out at s=7, 8, and 13TeV in complementary production modes. The combined upper limit at 95% confidence level on B(H→inv) is 0.15 (0.08 expected).

Measurement of the top quark mass using a profile likelihood approach with the lepton + jets final states in proton-proton collisions at s=13TeV.

The mass of the top quark is measured in 36.3fb-1 of LHC proton-proton collision data collected with the CMS detector at s=13TeV. The measurement uses a sample of top quark pair candidate events containing one isolated electron or muon and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a top quark pair hypothesis. A profile likelihood method is applied using up to four observables per event to extract the top quark mass. The top quark mass is measured to be 171.77±0.37GeV. This approach significantly improves the precision over previous measurements.

Search for Exotic Higgs Boson Decays H→AA→4γ with Events Containing Two Merged Diphotons in Proton-Proton Collisions at sqrt[s]=13 TeV.

We present the first direct search for exotic Higgs boson decays H→AA, A→γγ in events with two photonlike objects. The hypothetical particle A is a low-mass spin-0 particle decaying promptly to a merged diphoton reconstructed as a single photonlike object. We analyze the data collected by the CMS experiment at sqrt[s]=13 TeV corresponding to an integrated luminosity of 136 fb^{-1}. No excess above the estimated background is found. We set upper limits on the branching fraction B(H→AA→4γ) of (0.9-3.3)×10^{-3} at 95% confidence level for masses of A in the range 0.1-1.2 GeV.

Observation of Same-Sign WW Production from Double Parton Scattering in Proton-Proton Collisions at sqrt[s]=13 TeV.

The first observation of the production of W^{±}W^{±} bosons from double parton scattering processes using same-sign electron-muon and dimuon events in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of 138 fb^{-1} recorded at a center-of-mass energy of 13 TeV using the CMS detector at the CERN LHC. Multivariate discriminants are used to distinguish the signal process from the main backgrounds. A binned maximum likelihood fit is performed to extract the signal cross section. The measured cross section for production of same-sign W bosons decaying leptonically is 80.7±11.2(stat) _{-8.6}^{+9.5}(syst)±12.1(model) fb, whereas the measured fiducial cross section is 6.28±0.81(stat)±0.69(syst)±0.37(model) fb. The observed significance of the signal is 6.2 standard deviations above the background-only hypothesis.

Search for Higgs Boson and Observation of Z Boson through Their Decay into a Charm Quark-Antiquark Pair in Boosted Topologies in Proton-Proton Collisions at sqrt[s]=13 TeV.

A search for the standard model (SM) Higgs boson (H) produced with transverse momentum (p_{T}) greater than 450 GeV and decaying to a charm quark-antiquark (cc[over ¯]) pair is presented. The search is performed using proton-proton collision data collected at sqrt[s]=13 TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb^{-1}. Boosted H→cc[over ¯] decay products are reconstructed as a single large-radius jet and identified using a deep neural network charm tagging technique. The method is validated by measuring the Z→cc[over ¯] decay process, which is observed in association with jets at high p_{T} for the first time with a signal strength of 1.00_{-0.14}^{+0.17}(syst)±0.08(theo)±0.06(stat), defined as the ratio of the observed process rate to the SM expectation. The observed (expected) upper limit on σ(H)B(H→cc[over ¯]) is set at 47 (39) times the SM prediction at 95% confidence level.

Search for Nonresonant Pair Production of Highly Energetic Higgs Bosons Decaying to Bottom Quarks.

A search for nonresonant Higgs boson (H) pair production via gluon and vector boson (V) fusion is performed in the four-bottom-quark final state, using proton-proton collision data at 13 TeV corresponding to 138 fb^{-1} collected by the CMS experiment at the LHC. The analysis targets Lorentz-boosted H pairs identified using a graph neural network. It constrains the strengths relative to the standard model of the H self-coupling and the quartic VVHH couplings, κ_{2V}, excluding κ_{2V}=0 for the first time, with a significance of 6.3 standard deviations when other H couplings are fixed to their standard model values.

Measurements of jet multiplicity and jet transverse momentum in multijet events in proton-proton collisions at s=13TeV.

Multijet events at large transverse momentum (pT) are measured at s=13TeV using data recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 36.3fb-1. The multiplicity of jets with pT>50GeV that are produced in association with a high-pT dijet system is measured in various ranges of the pT of the jet with the highest transverse momentum and as a function of the azimuthal angle difference Δϕ1,2 between the two highest pT jets in the dijet system. The differential production cross sections are measured as a function of the transverse momenta of the four highest pT jets. The measurements are compared with leading and next-to-leading order matrix element calculations supplemented with simulations of parton shower, hadronization, and multiparton interactions. In addition, the measurements are compared with next-to-leading order matrix element calculations combined with transverse-momentum dependent parton densities and transverse-momentum dependent parton shower.

Search for Higgs Boson Decay to a Charm Quark-Antiquark Pair in Proton-Proton Collisions at sqrt[s]=13 TeV.

A search for the standard model Higgs boson decaying to a charm quark-antiquark pair, H→cc[over ¯], produced in association with a leptonically decaying V (W or Z) boson is presented. The search is performed with proton-proton collisions at sqrt[s]=13 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 138 fb^{-1}. Novel charm jet identification and analysis methods using machine learning techniques are employed. The analysis is validated by searching for Z→cc[over ¯] in VZ events, leading to its first observation at a hadron collider with a significance of 5.7 standard deviations. The observed (expected) upper limit on σ(VH)B(H→cc[over ¯]) is 0.94 (0.50_{-0.15}^{+0.22})pb at 95% confidence level (C.L.), corresponding to 14 (7.6_{-2.3}^{+3.4}) times the standard model prediction. For the Higgs-charm Yukawa coupling modifier, κ_{c}, the observed (expected) 95% C.L. interval is 1.1<|κ_{c}|<5.5 (|κ_{c}|<3.4), the most stringent constraint to date.

Azimuthal Correlations within Exclusive Dijets with Large Momentum Transfer in Photon-Lead Collisions.

The structure of nucleons is multidimensional and depends on the transverse momenta, spatial geometry, and polarization of the constituent partons. Such a structure can be studied using high-energy photons produced in ultraperipheral heavy-ion collisions. The first measurement of the azimuthal angular correlations of exclusively produced events with two jets in photon-lead interactions at large momentum transfer is presented, a process that is considered to be sensitive to the underlying nuclear gluon polarization. This study uses a data sample of ultraperipheral lead-lead collisions at sqrt[s_{NN}]=5.02 TeV, corresponding to an integrated luminosity of 0.38 nb^{-1}, collected with the CMS experiment at the LHC. The measured second harmonic of the correlation between the sum and difference of the two jet transverse momentum vectors is found to be positive, and rising, as the dijet transverse momentum increases. A well-tuned model that has been successful at describing a wide range of proton scattering data from the HERA experiments fails to describe the observed correlations, suggesting the presence of gluon polarization effects.

Azimuthal correlations in Z +jets events in proton-proton collisions at s=13TeV.

The production of Z bosons associated with jets is measured in pp collisions at s=13TeV with data recorded with the CMS experiment at the LHC corresponding to an integrated luminosity of 36.3fb-1. The multiplicity of jets with transverse momentum pT>30GeV is measured for different regions of the Z boson's pT(Z), from lower than 10GeV to higher than 100GeV. The azimuthal correlation Δϕ between the Z boson and the leading jet, as well as the correlations between the two leading jets are measured in three regions of pT(Z). The measurements are compared with several predictions at leading and next-to-leading orders, interfaced with parton showers. Predictions based on transverse-momentum dependent parton distributions and corresponding parton showers give a good description of the measurement in the regions where multiple parton interactions and higher jet multiplicities are not important. The effects of multiple parton interactions are shown to be important to correctly describe the measured spectra in the low pT(Z) regions.

Measurements of the Higgs boson production cross section and couplings in the W boson pair decay channel in proton-proton collisions at s=13TeV.

Production cross sections of the standard model Higgs boson decaying to a pair of W bosons are measured in proton-proton collisions at a center-of-mass energy of 13TeV. The analysis targets Higgs bosons produced via gluon fusion, vector boson fusion, and in association with a W or Z boson. Candidate events are required to have at least two charged leptons and moderate missing transverse momentum, targeting events with at least one leptonically decaying W boson originating from the Higgs boson. Results are presented in the form of inclusive and differential cross sections in the simplified template cross section framework, as well as couplings of the Higgs boson to vector bosons and fermions. The data set collected by the CMS detector during 2016-2018 is used, corresponding to an integrated luminosity of 138fb-1. The signal strength modifier µ, defined as the ratio of the observed production rate in a given decay channel to the standard model expectation, is measured to be µ=0.95-0.09+0.10. All results are found to be compatible with the standard model within the uncertainties.

Search for light Higgs bosons from supersymmetric cascade decays in pp collisions at s=13TeV.

A search is reported for pairs of light Higgs bosons (H1) produced in supersymmetric cascade decays in final states with small missing transverse momentum. A data set of LHC pp collisions collected with the CMS detector at s=13TeV and corresponding to an integrated luminosity of 138fb-1 is used. The search targets events where both H1 bosons decay into pairs that are reconstructed as large-radius jets using substructure techniques. No evidence is found for an excess of events beyond the background expectations of the standard model (SM). Results from the search are interpreted in the next-to-minimal supersymmetric extension of the SM, where a "singlino" of small mass leads to squark and gluino cascade decays that can predominantly end in a highly Lorentz-boosted singlet-like H1 and a singlino-like neutralino of small transverse momentum. Upper limits are set on the product of the squark or gluino pair production cross section and the square of the branching fraction of the H1 in a benchmark model containing almost mass-degenerate gluinos and light-flavour squarks. Under the assumption of an SM-like branching fraction, H1 bosons with masses in the range 40-120GeV arising from the decays of squarks or gluinos with a mass of 1200-2500GeV are excluded at 95% confidence level.

Measurement of the differential tt¯ production cross section as a function of the jet mass and extraction of the top quark mass in hadronic decays of boosted top quarks.

A measurement of the jet mass distribution in hadronic decays of Lorentz-boosted top quarks is presented. The measurement is performed in the lepton + jets channel of top quark pair production (tt¯) events, where the lepton is an electron or muon. The products of the hadronic top quark decay are reconstructed using a single large-radius jet with transverse momentum greater than 400GeV. The data were collected with the CMS detector at the LHC in proton-proton collisions and correspond to an integrated luminosity of 138fb-1. The differential tt¯ production cross section as a function of the jet mass is unfolded to the particle level and is used to extract the top quark mass. The jet mass scale is calibrated using the hadronic W boson decay within the large-radius jet. The uncertainties in the modelling of the final state radiation are reduced by studying angular correlations in the jet substructure. These developments lead to a significant increase in precision, and a top quark mass of 173.06±0.84GeV.

CMS pythia 8 colour reconnection tunes based on underlying-event data.

New sets of parameter tunes for two of the colour reconnection models, quantum chromodynamics-inspired and gluon-move, implemented in the pythia  8 event generator, are obtained based on the default CMS pythia  8 underlying-event tune, CP5. Measurements sensitive to the underlying event performed by the CMS experiment at centre-of-mass energies s=7 and 13TeV, and by the CDF experiment at 1.96TeV are used to constrain the parameters of colour reconnection models and multiple-parton interactions simultaneously. The new colour reconnection tunes are compared with various measurements at 1.96, 7, 8, and 13TeV including measurements of the underlying-event, strange-particle multiplicities, jet substructure observables, jet shapes, and colour flow in top quark pair (tt¯) events. The new tunes are also used to estimate the uncertainty related to colour reconnection modelling in the top quark mass measurement using the decay products of tt¯ events in the semileptonic channel at 13TeV.

Probing Heavy Majorana Neutrinos and the Weinberg Operator through Vector Boson Fusion Processes in Proton-Proton Collisions at sqrt[s]=13 TeV.

The first search exploiting the vector boson fusion process to probe heavy Majorana neutrinos and the Weinberg operator at the LHC is presented. The search is performed in the same-sign dimuon final state using a proton-proton collision dataset recorded at sqrt[s]=13 TeV, collected with the CMS detector and corresponding to a total integrated luminosity of 138 fb^{-1}. The results are found to agree with the predictions of the standard model. For heavy Majorana neutrinos, constraints on the squared mixing element between the muon and the heavy neutrino are derived in the heavy neutrino mass range 50 GeV-25 TeV; for masses above 650 GeV these are the most stringent constraints from searches at the LHC to date. A first test of the Weinberg operator at colliders provides an observed upper limit at 95% confidence level on the effective µµ Majorana neutrino mass of 10.8 GeV.

Measurement of the mass dependence of the transverse momentum of lepton pairs in Drell-Yan production in proton-proton collisions at s=13TeV.

The double differential cross sections of the Drell-Yan lepton pair (ℓ+ℓ-, dielectron or dimuon) production are measured as functions of the invariant mass mℓℓ, transverse momentum pT(ℓℓ), and φη∗. The φη∗ observable, derived from angular measurements of the leptons and highly correlated with pT(ℓℓ), is used to probe the low-pT(ℓℓ) region in a complementary way. Dilepton masses up to 1TeV are investigated. Additionally, a measurement is performed requiring at least one jet in the final state. To benefit from partial cancellation of the systematic uncertainty, the ratios of the differential cross sections for various mℓℓ ranges to those in the Z mass peak interval are presented. The collected data correspond to an integrated luminosity of 36.3fb-1 of proton-proton collisions recorded with the CMS detector at the LHC at a centre-of-mass energy of 13TeV. Measurements are compared with predictions based on perturbative quantum chromodynamics, including soft-gluon resummation.

Measurements of the associated production of a W boson and a charm quark in proton-proton collisions at s = 8 TeV.

Measurements of the associated production of a W boson and a charm ( c ) quark in proton-proton collisions at a centre-of-mass energy of 8 TeV are reported. The analysis uses a data sample corresponding to a total integrated luminosity of 19.7 fb - 1 collected by 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 quark jets are selected using distinctive signatures of charm hadron decays. The product of the cross section and branching fraction σ ( pp → W + c + X ) B ( W → ℓ ν ) , where ℓ = e or µ , and the cross section ratio σ ( pp → W + + c ¯ + X ) / σ ( pp → W - + c + X ) are measured in a fiducial volume and differentially as functions of the pseudorapidity and of the transverse momentum of the lepton from the W boson decay. The results are compared with theoretical predictions. The impact of these measurements on the determination of the strange quark distribution is assessed.

Search for Higgs Boson Pair Production in the Four b Quark Final State in Proton-Proton Collisions at sqrt[s]=13 TeV.

A search for pairs of Higgs bosons produced via gluon and vector boson fusion is presented, focusing on the four b quark final state. The data sample consists of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC, and corresponds to an integrated luminosity of 138 fb^{-1}. No deviation from the background-only hypothesis is observed. A 95% confidence level upper limit on the Higgs boson pair production cross section is observed at 3.9 times the standard model prediction for an expected value of 7.8. Constraints are also set on the modifiers of the Higgs field self-coupling, κ_{λ}, and of the coupling of two Higgs bosons to two vector bosons, κ_{2 V}. The observed (expected) allowed intervals at the 95% confidence level are -2.3<κ_{λ}<9.4 (-5.0<κ_{λ}<12.0) and -0.1<κ_{2 V}<2.2 (-0.4<κ_{2 V}<2.5). These are the most stringent observed constraints to date on the HH production cross section and on the κ_{2 V } coupling.