The observation of the standard model (SM) Higgs boson decay to a pair of bottom quarks is presented. The main contribution to this result is from processes in which Higgs bosons are produced in association with a W or Z boson (VH), and are searched for in final states including 0, 1, or 2 charged leptons and two identified bottom quark jets. The results from the measurement of these processes in a data sample recorded by the CMS experiment in 2017, comprising 41.3 fb^{-1} of proton-proton collisions at sqrt[s]=13 TeV, are described. When combined with previous VH measurements using data collected at sqrt[s]=7, 8, and 13 TeV, an excess of events is observed at m_{H}=125 GeV with a significance of 4.8 standard deviations, where the expectation for the SM Higgs boson is 4.9. The corresponding measured signal strength is 1.01±0.22. The combination of this result with searches by the CMS experiment for H→bb[over ¯] in other production processes yields an observed (expected) significance of 5.6 (5.5) standard deviations and a signal strength of 1.04±0.20.
The pseudorapidity distributions of dijets as functions of their average transverse momentum (p_{T}^{ave}) are measured in proton-lead (pPb) and proton-proton (pp) collisions. The data samples were collected by the CMS experiment at the CERN LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. A significant modification of the pPb spectra with respect to the pp spectra is observed in all p_{T}^{ave} intervals investigated. The ratios of the pPb and pp distributions are compared to next-to-leading order perturbative quantum chromodynamics calculations with unbound nucleon and nuclear parton distribution functions (PDFs). These results give the first evidence that the gluon PDF at large Bjorken x in lead ions is strongly suppressed with respect to the PDF in unbound nucleons.
The elliptic azimuthal anisotropy coefficient (v_{2}) is measured for charm (D^{0}) and strange (K_{S}^{0}, Λ, Ξ^{-}, and Ω^{-}) hadrons, using a data sample of p+Pb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy of sqrt[s_{NN}]=8.16 TeV. A significant positive v_{2} signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity p+Pb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller v_{2} than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at sqrt[s_{NN}]=5.02 TeV, also presented.
A search for a light charged Higgs boson (H^{+}) decaying to a W boson and a CP-odd Higgs boson (A) in final states with eμμ or μμμ is performed using data from pp collisions at sqrt[s]=13 TeV, recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb^{-1}. In this search, it is assumed that the H^{+} boson is produced in decays of top quarks, and the A boson decays to two oppositely charged muons. The presence of signals for H^{+} boson masses between 100 and 160 GeV and A boson masses between 15 and 75 GeV is investigated. No evidence for the production of the H^{+} boson is found. Upper limits at 95% confidence level are obtained on the combined branching fraction for the decay chain, t→bH^{+}→bW^{+}A→bW^{+}μ^{+}μ^{-}, of 1.9×10^{-6} to 8.6×10^{-6}, depending on the masses of the H^{+} and A bosons. These are the first limits for these decay modes of the H^{+} and A bosons.
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[over ˜]) in supersymmetric models that exhibit coannihilation between the τ[over ˜] and the lightest neutralino (χ[over ˜]_{1}^{0}), 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 sqrt[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 (χ[over ˜]_{1}^{±}) or next-to-lightest neutralino (χ[over ˜]_{2}^{0}), and the χ[over ˜]_{1}^{0}. The mass of the τ[over ˜] is assumed to be the average of the χ[over ˜]_{1}^{±} and χ[over ˜]_{1}^{0} masses. The data are consistent with standard model background predictions. Upper limits at 95% confidence level are set on the sum of the χ[over ˜]_{1}^{±}, χ[over ˜]_{2}^{0}, and τ[over ˜] production cross sections for Δm(χ[over ˜]_{1}^{±},χ[over ˜]_{1}^{0})=50 GeV, resulting in a lower limit of 290 GeV on the mass of the χ[over ˜]_{1}^{±}, which is the most stringent to date and surpasses the bounds from the LEP experiments.
A search for narrow low-mass resonances decaying to quark-antiquark pairs is presented. The search is based on proton-proton collision events collected at 13 TeV by the CMS detector at the CERN LHC. The data sample corresponds to an integrated luminosity of 35.9 fb^{-1}, recorded in 2016. The search considers the case where the resonance has high transverse momentum due to initial-state radiation of a hard photon. To study this process, the decay products of the resonance are reconstructed as a single large-radius jet with two-pronged substructure. The signal would be identified as a localized excess in the jet invariant mass spectrum. No evidence for such a resonance is observed in the mass range 10 to 125 GeV. Upper limits at the 95% confidence level are set on the coupling strength of resonances decaying to quark pairs. The results obtained with this photon trigger strategy provide the first direct constraints on quark-antiquark resonance masses below 50 GeV obtained at a hadron collider.
A search for the Higgs boson decaying to two oppositely charged muons is presented using data recorded by the CMS experiment at the CERN LHC in 2016 at a center-of-mass energy sqrt[s]=13 TeV, corresponding to an integrated luminosity of 35.9 fb^{-1}. Data are found to be compatible with the predicted background. For a Higgs boson with a mass of 125.09 GeV, the 95% confidence level observed (background-only expected) upper limit on the production cross section times the branching fraction to a pair of muons is found to be 3.0 (2.5) times the standard model expectation. In combination with data recorded at center-of-mass energies sqrt[s]=7 and 8 TeV, the background-only expected upper limit improves to 2.2 times the standard model value with a standard model expected significance of 1.0 standard deviation. The corresponding observed upper limit is 2.9 with an observed significance of 0.9 standard deviation. This corresponds to an observed upper limit on the standard model Higgs boson branching fraction to muons of 6.4×10^{-4} and to an observed signal strength of 1.0±1.0(stat)±0.1(syst).
A search is presented for a narrow resonance decaying to a pair of oppositely charged muons using sqrt[s]=13 TeV proton-proton collision data recorded at the LHC. In the 45-75 and 110-200 GeV resonance mass ranges, the search is based on conventional triggering and event reconstruction techniques. In the 11.5-45 GeV mass range, the search uses data collected with dimuon triggers with low transverse momentum thresholds, recorded at high rate by storing a reduced amount of trigger-level information. The data correspond to integrated luminosities of 137 and 96.6 fb^{-1} for conventional and high-rate triggering, respectively. No significant resonant peaks are observed in the probed mass ranges. The search sets the most stringent constraints to date on a dark photon in the ∼30-75 and 110-200 GeV mass ranges.
Results are reported from a search for new particles that decay into a photon and two gluons, in events with jets. Novel jet substructure techniques are developed that allow photons to be identified in an environment densely populated with hadrons. The analyzed proton-proton collision data were collected by the CMS experiment at the LHC, in 2016 at sqrt[s]=13 TeV, and correspond to an integrated luminosity of 35.9 fb^{-1}. The spectra of total transverse hadronic energy of candidate events are examined for deviations from the standard model predictions. No statistically significant excess is observed over the expected background. The first cross section limits on new physics processes resulting in such events are set. The results are interpreted as upper limits on the rate of gluino pair production, utilizing a simplified stealth supersymmetry model. The excluded gluino masses extend up to 1.7 TeV, for a neutralino mass of 200 GeV and exceed previous mass constraints set by analyses targeting events with isolated photons.
A measurement is reported of the jet mass distribution in hadronic decays of boosted top quarks produced in pp collisions at sqrt[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+jets channel of tt[over ¯] events, where the lepton is an electron or muon. The products of the hadronic top quark decay t→bW→bqq[over ¯]^{'} are reconstructed as a single jet with transverse momentum larger than 400 GeV. The tt[over ¯] 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.
The polarizations of promptly produced χ_{c1} and χ_{c2} mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at sqrt[s]=8 TeV. The χ_{c} states are reconstructed via their radiative decays χ_{c}→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 χ_{c2} to χ_{c1} 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.
This paper presents new sets of parameters ("tunes") for the underlying-event model of the H E R W I G 7 event generator. These parameters control the description of multiple-parton interactions (MPI) and colour reconnection in H E R W I G 7 , and are obtained from a fit to minimum-bias data collected by the CMS experiment at s = 0.9 , 7, and 13 Te . The tunes are based on the NNPDF 3.1 next-to-next-to-leading-order parton distribution function (PDF) set for the parton shower, and either a leading-order or next-to-next-to-leading-order PDF set for the simulation of MPI and the beam remnants. Predictions utilizing the tunes are produced for event shape observables in electron-positron collisions, and for minimum-bias, inclusive jet, top quark pair, and Z and W boson events in proton-proton collisions, and are compared with data. Each of the new tunes describes the data at a reasonable level, and the tunes using a leading-order PDF for the simulation of MPI provide the best description of the data.
A search for standard model production of four top quarks ( t t ¯ t t ¯ ) is reported using events containing at least three leptons ( e , μ ) or a same-sign lepton pair. The events are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC, and the data sample, recorded in 2016, corresponds to an integrated luminosity of 35.9 fb - 1 . Jet multiplicity and flavor are used to enhance signal sensitivity, and dedicated control regions are used to constrain the dominant backgrounds. The observed and expected signal significances are, respectively, 1.6 and 1.0 standard deviations, and the t t ¯ t t ¯ cross section is measured to be 16 . 9 - 11.4 + 13.8 fb , in agreement with next-to-leading-order standard model predictions. These results are also used to constrain the Yukawa coupling between the top quark and the Higgs boson to be less than 2.1 times its expected standard model value at 95% confidence level.
Events with no charged particles produced between the two leading jets are studied in proton-proton collisions at s = 7 TeV . The jets were required to have transverse momentum p T jet > 40 GeV and pseudorapidity 1.5 < | η jet | < 4.7 , and to have values of η jet with opposite signs. The data used for this study were collected with the CMS detector during low-luminosity running at the LHC, and correspond to an integrated luminosity of 8 pb - 1 . Events with no charged particles with p T > 0.2 GeV in the interval - 1 < η < 1 between the jets are observed in excess of calculations that assume no color-singlet exchange. The fraction of events with such a rapidity gap, amounting to 0.5-1% of the selected dijet sample, is measured as a function of the p T of the second-leading jet and of the rapidity separation between the jets. The data are compared to previous measurements at the Tevatron, and to perturbative quantum chromodynamics calculations based on the Balitsky-Fadin-Kuraev-Lipatov evolution equations, including different models of the non-perturbative gap survival probability.
A measurement is presented of the triple-differential dijet cross section at a centre-of-mass energy of 8 TeV using 19.7 fb -1 of data collected with the CMS detector in proton-proton collisions at the LHC. The cross section is measured as a function of the average transverse momentum, half the rapidity separation, and the boost of the two leading jets in the event. The cross section is corrected for detector effects and compared to calculations in perturbative quantum chromodynamics at next-to-leading order accuracy, complemented with electroweak and nonperturbative corrections. New constraints on parton distribution functions are obtained and the inferred value of the strong coupling constant is α S ( M Z ) = 0.1199 ± 0.0015 ( exp ) - 0.0020 + 0.0031 ( theo ) , where M Z is the mass of the Z boson.
Inclusive jet production in pPb collisions at a nucleon-nucleon (NN) center-of-mass energy of [Formula: see text] is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 30.1 nb[Formula: see text] is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range [Formula: see text] in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about [Formula: see text] is observed in the measured kinematic range. The measurements in the pPb system are compared to reference jet spectra obtained by extrapolation from previous measurements in pp collisions at [Formula: see text]. In all pseudorapidity ranges, nuclear modifications in inclusive jet production are found to be small, as predicted by next-to-leading order perturbative QCD calculations that incorporate nuclear effects in the parton distribution functions.
The nuclear modification factors of J / ψ and ψ (2S) mesons are measured in PbPb collisions at a centre-of-mass energy per nucleon pair of s NN = 5.02 TeV . The analysis is based on PbPb and p p data samples collected by CMS at the LHC in 2015, corresponding to integrated luminosities of 464 μ b - 1 and 28 pb -1 , respectively. The measurements are performed in the dimuon rapidity range of | y | < 2.4 as a function of centrality, rapidity, and transverse momentum ( p T ) from p T = 3 GeV / c in the most forward region and up to 50 GeV / c . Both prompt and nonprompt (coming from b hadron decays) J / ψ mesons are observed to be increasingly suppressed with centrality, with a magnitude similar to the one observed at s NN = 2.76 TeV for the two J / ψ meson components. No dependence on rapidity is observed for either prompt or nonprompt J / ψ mesons. An indication of a lower prompt J / ψ meson suppression at p T > 25 GeV / c is seen with respect to that observed at intermediate p T . The prompt ψ (2S) meson yield is found to be more suppressed than that of the prompt J / ψ mesons in the entire p T range.
Measurements are presented of the lifetimes of the B 0 , B s 0 , Λ b 0 , and B c + hadrons using the decay channels B 0 → J / ψ K ∗ ( 892 ) 0 , B 0 → J / ψ K S 0 , B s 0 → J / ψ π + π - , B s 0 → J / ψ ϕ ( 1020 ) , Λ b 0 → J / ψ Λ 0 , and B c + → J / ψ π + . The data sample, corresponding to an integrated luminosity of 19.7 fb -1 , was collected by the CMS detector at the LHC in proton-proton collisions at s = 8 TeV . The B 0 lifetime is measured to be 453.0 ± 1.6 (stat) ± 1.8 (syst) μ m in J / ψ K ∗ ( 892 ) 0 and 457.8 ± 2.7 (stat) ± 2.8 (syst) μ m in J / ψ K S 0 , which results in a combined measurement of c τ B 0 = 454.1 ± 1.4 (stat) ± 1.7 (syst) μ m . The effective lifetime of the B s 0 meson is measured in two decay modes, with contributions from different amounts of the heavy and light eigenstates. This results in two different measured lifetimes: c τ B s 0 → J / ψ π + π - = 502.7 ± 10.2 (stat) ± 3.4 (syst) μ m and c τ B s 0 → J / ψ ϕ ( 1020 ) = 443.9 ± 2.0 (stat) ± 1.5 (syst) μ m . The Λ b 0 lifetime is found to be 442.9 ± 8.2 (stat) ± 2.8 (syst) μ m . The precision from each of these channels is as good as or better than previous measurements. The B c + lifetime, measured with respect to the B + to reduce the systematic uncertainty, is 162.3 ± 7.8 (stat) ± 4.2 (syst) ± 0.1 ( τ B + ) μ m . All results are in agreement with current world-average values.
A search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks is presented. Events with hadronic jets and one or two oppositely charged leptons are selected from a data sample corresponding to an integrated luminosity of 19.5[Formula: see text] collected by the CMS experiment at the LHC in [Formula: see text] collisions at a centre-of-mass energy of 8[Formula: see text]. In order to separate the signal from the larger [Formula: see text] + jets background, this analysis uses a matrix element method that assigns a probability density value to each reconstructed event under signal or background hypotheses. The ratio between the two values is used in a maximum likelihood fit to extract the signal yield. The results are presented in terms of the measured signal strength modifier, [Formula: see text], relative to the standard model prediction for a Higgs boson mass of 125[Formula: see text]. The observed (expected) exclusion limit at a 95 % confidence level is [Formula: see text] (3.3), corresponding to a best fit value [Formula: see text].
Properties of the Higgs boson with mass near 125[Formula: see text] are measured in proton-proton collisions with the CMS experiment at the LHC. Comprehensive sets of production and decay measurements are combined. The decay channels include [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] pairs. The data samples were collected in 2011 and 2012 and correspond to integrated luminosities of up to 5.1[Formula: see text] at 7[Formula: see text] and up to 19.7[Formula: see text] at 8[Formula: see text]. From the high-resolution [Formula: see text] and [Formula: see text] channels, the mass of the Higgs boson is determined to be [Formula: see text]. For this mass value, the event yields obtained in the different analyses tagging specific decay channels and production mechanisms are consistent with those expected for the standard model Higgs boson. The combined best-fit signal relative to the standard model expectation is [Formula: see text] at the measured mass. The couplings of the Higgs boson are probed for deviations in magnitude from the standard model predictions in multiple ways, including searches for invisible and undetected decays. No significant deviations are found.