ALBERT

Beschreibung: The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb−1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F0), left-handed (FL), or right-handed (FR) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −0.008 ± 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F0 (FL) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR), and left- and right-handed tensor (gL, gR) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR, [−0.08, 0.05] for gL, and [−0.04, 0.02] for gR, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.

Beschreibung: Normalised multi-differential cross sections for top quark pair ($$hbox {t}{ ar{hbox {t}}}$$tt¯) production are measured in proton-proton collisions at a centre-of-mass energy of 13$$,{ext {TeV}}$$TeV using events containing two oppositely charged leptons. The analysed data were recorded with the CMS detector in 2016 and correspond to an integrated luminosity of $$35.9{,{ext {fb}}^{-1}} $$35.9fb-1. The double-differential $$hbox {t}{ ar{hbox {t}}}$$tt¯ cross section is measured as a function of the kinematic properties of the top quark and of the $$hbox {t}{ ar{hbox {t}}}$$tt¯ system at parton level in the full phase space. A triple-differential measurement is performed as a function of the invariant mass and rapidity of the $$hbox {t}{ ar{hbox {t}}}$$tt¯ system and the multiplicity of additional jets at particle level. The data are compared to predictions of Monte Carlo event generators that complement next-to-leading-order (NLO) quantum chromodynamics (QCD) calculations with parton showers. Together with a fixed-order NLO QCD calculation, the triple-differential measurement is used to extract values of the strong coupling strength $$alpha _{S}$$αS and the top quark pole mass ($$m_{{ext {t}}}^{{ext {pole}}}$$mtpole) using several sets of parton distribution functions (PDFs). The measurement of $$m_{{ext {t}}}^{{ext {pole}}}$$mtpole exploits the sensitivity of the $$hbox {t}{ ar{hbox {t}}}$$tt¯ invariant mass distribution to $$m_{{ext {t}}}^{{ext {pole}}}$$mtpole near the production threshold. Furthermore, a simultaneous fit of the PDFs, $$alpha _{S}$$αS, and $$m_{{ext {t}}}^{{ext {pole}}}$$mtpole is performed at NLO, demonstrating that the new data have significant impact on the gluon PDF, and at the same time allow an accurate determination of $$alpha _{S}$$αS and $$m_{{ext {t}}}^{{ext {pole}}}$$mtpole. The values $$alpha _{S}(m_{{ext {Z}}}) = 0.1135{}^{+0.0021}_{-0.0017}$$αS(mZ)=0.1135-0.0017+0.0021 and $$m_{{ext {t}}}^{{ext {pole}}} = 170.5 pm 0.8 ,{ext {GeV}} $$mtpole=170.5±0.8GeV are extracted, which account for experimental and theoretical uncertainties, the latter being estimated from NLO scale variations. Possible effects from Coulomb and soft-gluon resummation near the $$hbox {t}{ ar{hbox {t}}}$$tt¯ production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of $$m_{{ext {t}}}^{{ext {pole}}}$$mtpole of the order of $$+1 ,{ext {GeV}} $$+1GeV, which can be regarded as additional theoretical uncertainty in the current $$m_{{ext {t}}}^{{ext {pole}}}$$mtpole extraction.

Beschreibung: Decays of the 125 GeV Higgs boson into a Z boson and a ρ0(770) or ϕ(1020) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at $$ sqrt{s} $$ s = 13 TeV. The analysed data set corresponds to an integrated luminosity of 137 fb−1. Events are selected in which the Z boson decays into a pair of electrons or a pair of muons, and the ρ and ϕ mesons decay into pairs of pions and kaons, respectively. No significant excess above the background model is observed. As different polarization states are possible for the decay products of the Z boson and ρ or ϕ mesons, affecting the signal acceptance, scenarios in which the decays are longitudinally or transversely polarized are considered. Upper limits at the 95% confidence level on the Higgs boson branching fractions into Zρ and Zϕ are determined to be 1.04–1.31% and 0.31–0.40%, respectively, where the ranges reflect the considered polarization scenarios; these values are 740–940 and 730–950 times larger than the respective standard model expectations. These results constitute the first experimental limits on the two decay channels.

Beschreibung: Measurements are presented of the single-diffractive dijet cross section and the diffractive cross section as a function of the proton fractional momentum loss $$xi $$ ξ and the four-momentum transfer squared t. Both processes $${ext{ p }{}{}} {ext{ p }{}{}} ightarrow {ext{ p }{}{}} {ext{ X }} $$ p p → p X and $${ext{ p }{}{}} {ext{ p }{}{}} ightarrow {ext{ X }} {ext{ p }{}{}} $$ p p → X p , i.e. with the proton scattering to either side of the interaction point, are measured, where $${ext{ X }} $$ X includes at least two jets; the results of the two processes are averaged. The analyses are based on data collected simultaneously with the CMS and TOTEM detectors at the LHC in proton–proton collisions at $$sqrt{s} = 8,ext {Te}ext {V} $$ s = 8 Te during a dedicated run with $$ eta ^{*} = 90,ext {m} $$ β ∗ = 90 m at low instantaneous luminosity and correspond to an integrated luminosity of $$37.5{,ext {nb}^{-1}} $$ 37.5 nb - 1 . The single-diffractive dijet cross section $$sigma ^{{ext{ p }{}{}} {ext{ X }}}_{mathrm {jj}}$$ σ jj p X , in the kinematic region $$xi 〈 0.1$$ ξ

Beschreibung: A search for standard model Higgs bosons (H) produced with transverse momentum (pT) greater than 450 GeV and decaying to bottom quark-antiquark pairs ($$ mathrm{b}overline{mathrm{b}} $$ b b ¯ ) is performed using proton-proton collision data collected by the CMS experiment at the LHC at $$ sqrt{s} $$ s = 13 TeV. The data sample corresponds to an integrated luminosity of 137 fb−1. The search is inclusive in the Higgs boson production mode. Highly Lorentz-boosted Higgs bosons decaying to $$ mathrm{b}overline{mathrm{b}} $$ b b ¯ are reconstructed as single large-radius jets, and are identified using jet substructure and a dedicated b tagging technique based on a deep neural network. The method is validated with Z →$$ mathrm{b}overline{mathrm{b}} $$ b b ¯ decays. For a Higgs boson mass of 125 GeV, an excess of events above the background assuming no Higgs boson production is observed with a local significance of 2.5 standard deviations (σ), while the expectation is 0.7. The corresponding signal strength and local significance with respect to the standard model expectation are μH = 3.7 ± 1.2(stat)$$ {}_{-0.7}^{+0.8} $$ − 0.7 + 0.8 (syst)$$ {}_{-0.5}^{+0.8} $$ − 0.5 + 0.8 (theo) and 1.9 σ. Additionally, an unfolded differential cross section as a function of Higgs boson pT for the gluon fusion production mode is presented, assuming the other production modes occur at the expected rates.

Beschreibung: A search for new physics in events with two highly Lorentz-boosted Z bosons and large missing transverse momentum is presented. The analyzed proton-proton collision data, corresponding to an integrated luminosity of 137 fb−1, were recorded at $$ sqrt{s} $$ s = 13 TeV by the CMS experiment at the CERN LHC. The search utilizes the substructure of jets with large radius to identify quark pairs from Z boson decays. Backgrounds from standard model processes are suppressed by requirements on the jet mass and the missing transverse momentum. No significant excess in the event yield is observed beyond the number of background events expected from the standard model. For a simplified supersymmetric model in which the Z bosons arise from the decay of gluinos, an exclusion limit of 1920 GeV on the gluino mass is set at 95% confidence level. This is the first search for beyond-standard-model production of pairs of boosted Z bosons plus large missing transverse momentum.

Beschreibung: A data sample of events from proton-proton collisions with at least two jets, and two isolated same-sign or three or more charged leptons, is studied in a search for signatures of new physics phenomena. The data correspond to an integrated luminosity of $$137{,{ext {fb}}^{-1}} $$137fb-1 at a center-of-mass energy of $$13,{ext {TeV}} $$13TeV, collected in 2016–2018 by the CMS experiment at the LHC. The search is performed using a total of 168 signal regions defined using several kinematic variables. The properties of the events are found to be consistent with the expectations from standard model processes. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos or squarks for various decay scenarios in the context of supersymmetric models conserving or violating R parity. The observed lower mass limits are as large as $$2.1,{ext {TeV}} $$2.1TeV for gluinos and $$0.9,{ext {TeV}} $$0.9TeV for top and bottom squarks. To facilitate reinterpretations, model-independent limits are provided in a set of simplified signal regions.