Search

Results are reported from a search for the lepton flavor violating decay τ → 3μ in proton-proton collisions at s = 13 TeV. The data sample corresponds to an integrated luminosity of 33.2 fb −1 recorded by the CMS experiment at the LHC in 2016. The search exploits τ leptons produced in both W boson and heavy-flavor hadron decays. No significant excess above the expected background is observed. An upper limit on the branching fraction ℬ(τ → 3μ) of 8.0 × 10 −8 at 90% confidence level is obtained, with an expected upper limit of 6.9 × 10 −8. [Figure not available: see fulltext.]

The dependence of inclusive jet production in proton-proton collisions with a center-of-mass energy of 13 TeV on the distance parameter R of the anti-k T algorithm is studied using data corresponding to integrated luminosities up to 35.9 fb −1 collected by the CMS experiment in 2016. The ratios of the inclusive cross sections as functions of transverse momentum p T and rapidity y, for R in the range 0.1 to 1.2 to those using R = 0.4 are presented in the region 84 < p T< 1588 GeV and |y|< 2.0. The results are compared to calculations at leading and next-to-leading order in the strong coupling constant using different parton shower models. The variation of the ratio of cross sections with R is well described by calculations including a parton shower model, but not by a leading-order quantum chromodynamics calculation including nonperturbative effects. The agreement between the data and the theoretical predictions for the ratios of cross sections is significantly improved when next-to-leading order calculations with nonperturbative effects are used. [Figure not available: see fulltext.].

The differential cross section and charge asymmetry for inclusive W boson production at s=13 TeV is measured for the two transverse polarization states as a function of the W boson absolute rapidity. The measurement uses events in which a W boson decays to a neutrino and either a muon or an electron. The data sample of proton-proton collisions recorded with the CMS detector at the LHC in 2016 corresponds to an integrated luminosity of 35.9 fb-1. The differential cross section and its value normalized to the total inclusive W boson production cross section are measured over the rapidity range |yW

A measurement of the W+W- boson pair production cross section in proton-proton collisions at s=13 TeV is presented. The data used in this study are collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 35.9 fb-1. The W+W- candidate events are selected by requiring two oppositely charged leptons (electrons or muons). Two methods for reducing background contributions are employed. In the first one, a sequence of requirements on kinematic quantities is applied allowing a measurement of the total production cross section, 117.6±6.8 pb, which agrees well with the theoretical prediction. Fiducial cross sections are also reported for events with zero or one jet, and the change in the zero-jet fiducial cross section with the jet transverse momentum threshold is measured. Normalized differential cross sections are reported within the fiducial region. A second method for suppressing background contributions employs two random forest classifiers. The analysis based on this method includes a measurement of the total production cross section and also a measurement of the normalized jet multiplicity distribution in W+W- events. Finally, a dilepton invariant mass distribution is used to probe for physics beyond the standard model in the context of an effective field theory, and constraints on the presence of dimension-6 operators are derived.

Measurements of production cross sections of WZ and same-sign WW boson pairs in association with two jets in proton-proton collisions at s=13TeV at the LHC are reported. The data sample corresponds to an integrated luminosity of 137fb −1, collected with the CMS detector during 2016–2018. The measurements are performed in the leptonic decay modes [Formula presented] and [Formula presented], where ℓ,ℓ ′=e, [Formula presented]. Differential fiducial cross sections as functions of the invariant masses of the jet and charged lepton pairs, as well as of the leading-lepton transverse momentum, are measured for W ±W ± production and are consistent with the standard model predictions. The dependence of differential cross sections on the invariant mass of the jet pair is also measured for WZ production. An observation of electroweak production of WZ boson pairs is reported with an observed (expected) significance of 6.8 (5.3) standard deviations. Constraints are obtained on the structure of quartic vector boson interactions in the framework of effective field theory.

The first observation is reported of the combined production of three massive gauge bosons (VVV with V = W,Z) in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis is based on a data sample recorded by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 137 fb$^{-1}$. The searches for individual WWW, WWZ, WZZ, and ZZZ production are performed in final states with three, four, five, and six leptons (electrons or muons), or with two same-sign leptons plus one or two jets. The observed (expected) significance of the combined VVV production signal is 5.7 (5.9) standard deviations and the corresponding measured cross section relative to the standard model prediction is 1.02 $^{+0.26}_{-0.23}$. The significances of the individual WWW and WWZ production are 3.3 and 3.4 standard deviations, respectively. Measured production cross sections for the individual triboson processes are also reported.

The first direct, model-independent measurement is presented of the modulus of the Cabibbo–Kobayashi–Maskawa (CKM) matrix elements |η|V tb, |η|V td, and |η|V ts, in final states enriched in single top quark t-channel events. The analysis uses proton-proton collision data from the LHC, collected during 2016 by the CMS experiment, at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb −1. Processes directly sensitive to these matrix elements are considered at both the production and decay vertices of the top quark. In the standard model hypothesis of CKM unitarity, a lower limit of |η|V tb>0.970 is measured at the 95% confidence level. Several theories beyond the standard model are considered, and by releasing all constraints among the involved parameters, the values |η|V tb=0.988±0.024, and |η|V td 2+|η|V ts 2=0.06±0.06, where the uncertainties include both statistical and systematic components, are measured.

The fiducial cross section for Y(1S) pair production in proton-proton collisions at a center-of-mass energy of 13 TeV in the region where both Y(1S) mesons have an absolute rapidity below 2.0 is measured to be 79±11(stat)±6(syst)±3(B) pb assuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y(1S) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9fb −1. This process serves as a standard model reference in a search for narrow resonances decaying to Y(1S)μ +μ − in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two b quarks and two b¯ antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y(1S) resonance are set as a function of the resonance mass.

The first observation of the tt¯H process in a single Higgs boson decay channel with the full reconstruction of the final state (H→γγ) is presented, with a significance of 6.6 standard deviations (σ). The CP structure of Higgs boson couplings to fermions is measured, resulting in an exclusion of the pure CP-odd structure of the top Yukawa coupling at 3.2σ. The measurements are based on a sample of proton-proton collisions at a center-of-mass energy s=13 TeV collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb-1. The cross section times branching fraction of the tt¯H process is measured to be σtt¯HBγγ=1.56-0.32+0.34 fb, which is compatible with the standard model prediction of 1.13-0.11+0.08 fb. The fractional contribution of the CP-odd component is measured to be fCPHtt=0.00±0.33.

A search for the production of a narrow-width resonance decaying into a pair of Higgs bosons decaying into the bbZZ channel is presented. The analysis is based on data collected with the CMS detector during 2016, in proton-proton collisions at the LHC, corresponding to an integrated luminosity of 35.9 fb-1. The final states considered are the ones where one of the Z bosons decays into a pair of muons or electrons, and the other Z boson decays to either a pair of quarks or a pair of neutrinos. Upper limits at 95% confidence level are placed on the production of narrow-width spin-0 or spin-2 particles decaying to a pair of Higgs bosons, in models with and without an extended Higgs sector. For a resonance mass range between 260 and 1000 GeV, limits on the production cross section times branching fraction of a spin-0 and spin-2 resonance range from 0.1 to 5.0 pb and 0.1 to 3.6 pb, respectively. These results set limits in parameter space in bulk Randall-Sundrum radion, Kaluza-Klein excitation of the graviton, andnext-to-minimal two-Higgs doublet models (N2HDMs). For specific choices of parameters the N2HDM can be excluded in a mass range between 360 and 620 GeV for a resonance decaying to two Higgs bosons. This is the first search for Higgs boson resonant pair production in the bbZZ channel.

Ratios of cross sections, σ(Z+c jets)/σ(Z+jets), σ(Z+b jets)/σ(Z+jets), and σ(Z+c jets)/σ(Z+b jets) in the associated production of a Z boson with at least one charm or bottom quark jet are measured in proton-proton collisions at s=13 TeV. The data sample, collected by the CMS experiment at the CERN LHC, corresponds to an integrated luminosity of 35.9 fb-1, with a fiducial volume of pT>30 GeV and |η|25 GeV and |η

Measurements of the cross section for the production of top quark pairs in association with a pair of jets from bottom quarks (σ t t ¯ b b ¯) and in association with a pair of jets from quarks of any flavor or gluons (σ t t ¯ jj) and their ratio are presented. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb −1. The measurements are performed in a fiducial phase space and extrapolated to the full phase space, separately for the dilepton and lepton+jets channels, where lepton corresponds to either an electron or a muon. The results of the measurements in the fiducial phase space for the dilepton and lepton+jets channels, respectively, are σ t t ¯ jj = 2.36±0.02 (stat)±0.20 (syst) pb and 31.0±0.2 (stat)±2.9 (syst) pb, and for the cross section ratio 0.017 ± 0.001 (stat) ± 0.001 (syst) and 0.020 ± 0.001 (stat) ± 0.001 (syst). The values of σ t t ¯ b b ¯ are determined from the product of the σ t t ¯ jj and the cross section ratio, obtaining, respectively, 0.040±0.002 (stat)±0.005 (syst) pb and 0.62±0.03 (stat)±0.07 (syst) pb. These measurements are the most precise to date and are consistent, within the uncertainties, with the standard model expectations obtained using a matrix element calculation at next-to-leading order in quantum chromodynamics matched to a parton shower. [Figure not available: see fulltext.]

A search is presented for long-lived charged particles that decay within the volume of the silicon tracker of the CMS experiment. Such particles can produce events with an isolated track that is missing hits in the outermost layers of the silicon tracker, and is also associated with little energy deposited in the calorimeters and no hits in the muon detectors. The search for events with this “disappearing track” signature is performed in a sample of proton-proton collisions recorded by the CMS experiment at the LHC with a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 101fb −1 recorded in 2017 and 2018. The observation of 48 events is consistent with the estimated background of 47.8 −2.3 +2.7(stat)±8.1(syst) events. Upper limits are set on chargino production in the context of an anomaly-mediated supersymmetry breaking model for purely wino and higgsino neutralino scenarios. At 95% confidence level, the first constraint is placed on chargino masses in the higgsino case, excluding below 750 (175) GeV for a lifetime of 3 (0.05) ns. In the wino case, the results of this search are combined with a previous CMS search to produce a result representing the complete LHC data set recorded in 2015–2018, the most stringent constraints to date. At 95% confidence level, chargino masses in the wino case are excluded below 884 (474) GeV for a lifetime of 3 (0.2) ns.

The transverse energy (ETγ) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at sNN = 5.02 TeV with integrated luminosities of 27.4 pb −1 and 404 μb −1 for pp and PbPb data, respectively. The results are presented for photons with 25

Anisotropies in the initial energy density distribution of the quark-gluon plasma created in high energy heavy ion collisions lead to anisotropies in the azimuthal distributions of the final-state particles known as collective anisotropic flow. Fourier harmonic decomposition is used to quantify these anisotropies. The higher-order harmonics can be induced by the same order anisotropies (linear response) or by the combined influence of several lower order anisotropies (nonlinear response) in the initial state. The mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles are measured as functions of transverse momentum and centrality in PbPb collisions at nucleon-nucleon center-of-mass energies s NN = 2.76 and 5.02 TeV with the CMS detector. The results are compared with viscous hydrodynamic calculations using several different initial conditions, as well as microscopic transport model calculations. None of the models provides a simultaneous description of the mixed higher-order flow harmonics and nonlinear response coefficients.

A search for a narrow resonance with a mass between 350 and 700 GeV, and decaying into a pair of jets, is performed using proton-proton collision events containing at least three jets. The data sample corresponds to an integrated luminosity of 18.3 fb −1 recorded at s=13TeV with the CMS detector. Data are collected with a technique known as “data scouting”, in which the events are reconstructed, selected, and recorded at a high rate in a compact form by the high-level trigger. The three-jet final state provides sensitivity to lower resonance masses than in previous searches using the data scouting technique. The spectrum of the dijet invariant mass, calculated from the two jets with the largest transverse momenta in the event, is used to search for a resonance. No significant excess over a smoothly falling background is found. Limits at 95% confidence level are set on the production cross section of a narrow dijet resonance and compared with the cross section of a vector dark matter mediator coupling to dark matter particles and quarks. Translating to a model where the narrow resonance interacts only with quarks, upper limits on this coupling range between 0.10 and 0.15, depending on the resonance mass. These results represent the most stringent upper limits in the mass range between 350 and 450 GeV obtained with a flavor-inclusive dijet resonance search.

A measurement is reported of the jet mass distribution in hadronic decays of boosted top quarks produced in pp collisions at √s = 13 TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 35.9 fb −1. The measurement is performed in the lepton þ jets channel of tt events, where the lepton is an electron or muon. The products of the hadronic top quark decay t → bW → bqq¯ 0 are reconstructed as a single jet with transverse momentum larger than 400 GeV. The t ¯t cross section as a function of the jet mass is unfolded at the particle level and used to extract a value of the top quark mass of 172.6 ± 2.5 GeV. A novel jet reconstruction technique is used for the first time at the LHC, which improves the precision by a factor of 3 relative to an earlier measurement. This highlights the potential of measurements using boosted top quarks, where the new technique will enable future precision measurements.

A study of the production of prompt J/$\psi$ mesons contained in jets in proton-proton collisions at $\sqrt{s} =$ 8 TeV is presented. The analysis is based on data corresponding to an integrated luminosity of 19.1 fb$^{-1}$ collected with the CMS detector at the LHC. For events with at least one observed jet, the angular separation between the J/$\psi$ meson and the jet is used to test whether the J/$\psi$ meson is part of the jet. The analysis shows that most prompt J/$\psi$ mesons with energy above 15 GeV and rapidity $|y

The polarizations of promptly produced χc1 and χc2 mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at s=8 TeV. The χc states are reconstructed via their radiative decays χc→J/ψγ, with the photons being measured through conversions to e+e-, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χc2 to χc1 yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ→μ+μ- decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.

The running of the top quark mass is experimentally investigated for the first time. The mass of the top quark in the modified minimal subtraction (MS‾) renormalization scheme is extracted from a comparison of the differential top quark-antiquark (tt¯) cross section as a function of the invariant mass of the tt¯ system to next-to-leading-order theoretical predictions. The differential cross section is determined at the parton level by means of a maximum-likelihood fit to distributions of final-state observables. The analysis is performed using tt¯ candidate events in the e ± μ ∓ channel in proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the CMS detector at the CERN LHC in 2016, corresponding to an integrated luminosity of 35.9fb −1. The extracted running is found to be compatible with the scale dependence predicted by the corresponding renormalization group equation. In this analysis, the running is probed up to a scale of the order of 1 TeV.

A measurement of the production cross section of top quark pairs in association with two b jets (tt‾bb‾) is presented using data collected in proton-proton collisions at s=13 TeV by the CMS detector at the LHC corresponding to an integrated luminosity of 35.9 fb −1. The cross section is measured in the all-jet decay channel of the top quark pair by selecting events containing at least eight jets, of which at least two are identified as originating from the hadronization of b quarks. A combination of multivariate analysis techniques is used to reduce the large background from multijet events not containing a top quark pair, and to help discriminate between jets originating from top quark decays and other additional jets. The cross section is determined for the total phase space to be 5.5±0.3(stat) −1.3 +1.6(syst)pb and also measured for two fiducial tt‾bb‾ definitions. The measured cross sections are found to be larger than theoretical predictions by a factor of 1.5–2.4, corresponding to 1–2 standard deviations.

Results are reported for the Bs0→ μ +μ − branching fraction and effective lifetime and from a search for the decay B 0→ μ +μ −. The analysis uses a data sample of proton-proton collisions accumulated by the CMS experiment in 2011, 2012, and 2016, with center-of-mass energies (integrated luminosities) of 7 TeV (5 fb −1), 8 TeV (20 fb −1), and 13 TeV (36 fb −1). The branching fractions are determined by measuring event yields relative to B +→ J/ψK + decays (with J/ψ → μ +μ −), which results in the reduction of many of the systematic uncertainties. The decay Bs0→ μ +μ − is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be ℬ(Bs0→μ+μ−)=[2.9±0.7(exp)±0.2(frag)]×10−9, where the first uncertainty combines the experimental statistical and systematic contributions, and the secondis due to the uncertainty in the ratio of the Bs0 and the B + fragmentation functions. No significant excess is observed for the decay B 0→ μ +μ −, and an upper limit of ℬ(B 0 → μ +μ −) < 3.6 × 10 −10 is obtained at 95% confidence level. The Bs0→ μ+μ− effective lifetime is measured to be τμ+μ−=1.70−0.44+0.61 ps. These results are consistent with standard model predictions. [Figure not available: see fulltext.].

Results are reported from a search for new physics beyond the standard model in proton-proton collisions in final states with a single lepton; multiple jets, including at least one jet tagged as originating from the hadronization of a bottom quark; and large missing transverse momentum. The search uses a sample of proton-proton collision data at s=13 TeV, corresponding to 137 fb-1, recorded by the CMS experiment at the LHC. The signal region is divided into categories characterized by the total number of jets, the number of bottom quark jets, the missing transverse momentum, and the sum of masses of large-radius jets. The observed event yields in the signal regions are consistent with estimates of standard model backgrounds based on event yields in the control regions. The results are interpreted in the context of simplified models of supersymmetry involving gluino pair production in which each gluino decays into a top quark-antiquark pair and a stable, unobserved neutralino, which generates missing transverse momentum in the event. Scenarios with gluino masses up to about 2150 GeV are excluded at 95% confidence level (or more) for neutralino masses up to 700 GeV. The highest excluded neutralino mass is about 1250 GeV, which holds for gluino masses around 1850 GeV.

This paper reports on a search for an extension to the scalar sector of the standard model, where a new CP-even (odd) boson decays to a Z boson and a lighter CP-odd (even) boson, and the latter further decays to a b quark pair. The Z boson is reconstructed via its decays to electron or muon pairs. The analysed data were recorded in proton-proton collisions at a center-of-mass energy s = 13 TeV, collected by the CMS experiment at the LHC during 2016, corresponding to an integrated luminosity of 35.9 fb −1. Data and predictions from the standard model are in agreement within the uncertainties. Upper limits at 95% confidence level are set on the production cross section times branching fraction, with masses of the new bosons up to 1000 GeV. The results are interpreted in the context of the two-Higgs-doublet model. [Figure not available: see fulltext.].

The observation of the Λ b 0→J/ψΛϕ decay is reported using proton-proton collision data collected at s=13TeV by the CMS experiment at the LHC in 2018, corresponding to an integrated luminosity of 60fb −1. The ratio of the branching fractions B(Λ b 0→J/ψΛϕ)/B(Λ b 0→ψ(2S)Λ) is measured to be (8.26±0.90(stat)±0.68(syst)±0.11(B))×10 −2, where the first uncertainty is statistical, the second is systematic, and the last uncertainty reflects the uncertainties in the world-average branching fractions of ϕ and ψ(2S) decays to the reconstructed final states.

A search is presented for τ slepton pairs produced in proton–proton collisions at a center-of-mass energy of 13TeV. The search is carried out in events containing two τ leptons in the final state, on the assumption that each τ slepton decays primarily to a τ lepton and a neutralino. Events are considered in which each τ lepton decays to one or more hadrons and a neutrino, or in which one of the τ leptons decays instead to an electron or a muon and two neutrinos. The data, collected with the CMS detector in 2016 and 2017, correspond to an integrated luminosity of 77.2fb-1. The observed data are consistent with the standard model background expectation. The results are used to set 95% confidence level upper limits on the cross section for τ slepton pair production in various models for τ slepton masses between 90 and 200GeV and neutralino masses of 1, 10, and 20GeV. In the case of purely left-handed τ slepton production and decay to a τ lepton and a neutralino with a mass of 1GeV, the strongest limit is obtained for a τ slepton mass of 125GeV at a factor of 1.14 larger than the theoretical cross section.

The first search for supersymmetry in events with an experimental signature of one soft, hadronically decaying τ lepton, one energetic jet from initial-state radiation, and large transverse momentum imbalance is presented. These event signatures are consistent with direct or indirect production of scalar τ leptons (τ) in supersymmetric models that exhibit coannihilation between the τ and the lightest neutralino (χ10), and that could generate the observed relic density of dark matter. The data correspond to an integrated luminosity of 77.2 fb-1 of proton-proton collisions at s=13 TeV collected with the CMS detector at the LHC in 2016 and 2017. The results are interpreted in a supersymmetric scenario with a small mass difference (Δm) between the chargino (χ1±) or next-to-lightest neutralino (χ20), and the χ10. The mass of the τ is assumed to be the average of the χ1± and χ10 masses. The data are consistent with standard model background predictions. Upper limits at 95% confidence level are set on the sum of theχ1±, χ20, and τ production cross sections for Δm(χ1±,χ10)=50 GeV, resulting in a lower limit of 290 GeV on the mass of the χ1±, which is the most stringent to date and surpasses the bounds from the LEP experiments.

Two related searches for phenomena beyond the standard model (BSM) are performed using events with hadronic jets and significant transverse momentum imbalance. The results are based on a sample of proton–proton collisions at a center-of-mass energy of 13TeV , collected by the CMS experiment at the LHC in 2016–2018 and corresponding to an integrated luminosity of 137 fb−1 . The first search is inclusive, based on signal regions defined by the hadronic energy in the event, the jet multiplicity, the number of jets identified as originating from bottom quarks, and the value of the kinematic variable 푀T2 for events with at least two jets. For events with exactly one jet, the transverse momentum of the jet is used instead. The second search looks in addition for disappearing tracks produced by BSM long-lived charged particles that decay within the volume of the tracking detector. No excess event yield is observed above the predicted standard model background. This is used to constrain a range of BSM models that predict the following: the pair production of gluinos and squarks in the context of supersymmetry models conserving R-parity, with or without intermediate long-lived charginos produced in the decay chain; the resonant production of a colored scalar state decaying to a massive Dirac fermion and a quark; or the pair production of scalar and vector leptoquarks each decaying to a neutrino and a top, bottom, or light-flavor quark. In most of the cases, the results obtained are the most stringent constraints to date.

A search for long-lived particles decaying to photons and weakly interacting particles, using proton-proton collision data at √ s = 13 TeV collected by the CMS experiment in 2016–2017 is presented. The data set corresponds to an integrated luminosity of 77.4 fb − 1 . Results are interpreted in the context of supersymmetry with gauge-mediated supersymmetry breaking, where the neutralino is long-lived and decays to a photon and a gravitino. Limits are presented as a function of the neutralino proper decay length and mass. For neutralino proper decay lengths of 0.1, 1, 10, and 100 m, masses up to 320, 525, 360, and 215 GeV are excluded at 95% confidence level, respectively. We extend the previous best limits in the neutralino proper decay length by up to one order of magnitude, and in the neutralino mass by up to 100 GeV.

A search for long-lived particles decaying to displaced, nonprompt jets and missing transverse momentum is presented. The data sample corresponds to an integrated luminosity of 137 fb −1 of proton-proton collisions at a center-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC in 2016–2018. Candidate signal events containing nonprompt jets are identified using the timing capabilities of the CMS electromagnetic calorimeter. The results of the search are consistent with the background prediction and are interpreted using a gauge-mediated supersymmetry breaking reference model with a gluino next-to-lightest supersymmetric particle. In this model, gluino masses up to 2100, 2500, and 1900 GeV are excluded at 95% confidence level for proper decay lengths of 0.3, 1, and 100 m, respectively. These are the best limits to date for such massive gluinos with proper decay lengths greater than ∼0.5 m.

This thesis sets out to test the current understanding of the pair production of the top quark standard model. To do so, it first introduces the theoretical knowledge behind the standard model and the production of the top quark, before discussing how the top quark is modelled in simulation. Next, the large and complex machinery required to produce and detect high-energy collisions is described and the algorithm used to reconstruct particles from the deposits. These particles are used to perform measurements of the differential $\mathrm{t}\overline{\mathrm{t}}}$ production cross sections. These are presented in the single-lepton ($e$ or $\mu$) decay channel, as a function of several kinematic event variables. These kinematic event variables do not require the reconstruction of the $\mathrm{t}\overline{\mathrm{t}}}$ system and are $N_{\mathrm{jets}}$, $H_{\mathrm{T}}$, $S_{\mathrm{T}}$, $p_{\mathrm{T}}^{\mathrm{miss}}$, $p_{\mathrm{T}}^{\mathrm{W}}$, $p_{\mathrm{T}}^{\ell}$ and $\lvert \eta^{\ell}} \rvert$. The measurements are performed with proton-proton collision data collected by the CMS experiment at the LHC during 2016, with an integrated luminosity of 35.9~$\mathrm{fb}^{-1}$. The $\mathrm{t}\overline{\mathrm{t}}}$ yield in each decay channel is calculated by subtracting the single top quark, vector boson in association with jets and multijet QCD production backgrounds from the total data yield. The $\mathrm{t}\overline{\mathrm{t}}}$ yields are then extrapolated, using a $\mathrm{t}\overline{\mathrm{t}}}$ model, with respect to the stable particles that form depositions detectable by CMS to a common phase space in order to be able to consistently combine the two channels. The data are also naturally smeared by the resolution of the detector and contain effects due to the detector efficiency and acceptance. The method to undo the thumbprint of the detector and to perform the extrapolation is discussed in detail. From the combined, unsmeared $\mathrm{t}\overline{\mathrm{t}}}$ yields, both the normalised and absolute differential cross sections are calculated together with the statistical and systematic uncertainties. The cross section measurements are compared to state-of-the-art leading order and next-to-leading order $\mathrm{t}\overline{\mathrm{t}}}$ simulations by means of a goodness-of-fit test, incorporating the total covariance matrix describing the correlations of the uncertainties between bins of the measurement. Finally, brief studies into the possible future of these differential cross sections measurements is discussed.