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: A search is presented for a Higgs boson that is produced via vector boson fusion and that decays to an undetected particle and an isolated photon. The search is performed by the CMS collaboration at the LHC, using a data set corresponding to an integrated luminosity of 130 fb−1, recorded at a center-of-mass energy of 13 TeV in 2016–2018. No significant excess of events above the expectation from the standard model background is found. The results are interpreted in the context of a theoretical model in which the undetected particle is a massless dark photon. An upper limit is set on the product of the cross section for production via vector boson fusion and the branching fraction for such a Higgs boson decay, as a function of the Higgs boson mass. For a Higgs boson mass of 125 GeV, assuming the standard model production rates, the observed (expected) 95% confidence level upper limit on the branching fraction is 3.5 (2.8)%. This is the first search for such decays in the vector boson fusion channel. Combination with a previous search for Higgs bosons produced in association with a Z boson results in an observed (expected) upper limit on the branching fraction of 2.9 (2.1)% at 95% confidence level.

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 phenomena beyond the standard model in final states with two oppositely charged same-flavor leptons and missing transverse momentum is presented. The search uses a data sample of proton-proton collisions at $$ sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 137 fb−1, collected by the CMS experiment at the LHC. Three potential signatures of physics beyond the standard model are explored: an excess of events with a lepton pair, whose invariant mass is consistent with the Z boson mass; a kinematic edge in the invariant mass distribution of the lepton pair; and the nonresonant production of two leptons. The observed event yields are consistent with those expected from standard model backgrounds. The results of the first search allow the exclusion of gluino masses up to 1870 GeV, as well as chargino (neutralino) masses up to 750 (800) GeV, while those of the searches for the other two signatures allow the exclusion of light-flavor (bottom) squark masses up to 1800 (1600) GeV and slepton masses up to 700 GeV, respectively, at 95% confidence level within certain supersymmetry scenarios.

Beschreibung: Angular distributions of the decay B+→ K∗(892)+μ+μ− are studied using events collected with the CMS detector in $$ sqrt{mathrm{s}} $$ s = 8 TeV proton-proton collisions at the LHC, corresponding to an integrated luminosity of 20.0 fb−1. The forward-backward asymmetry of the muons and the longitudinal polarization of the K∗(892)+ meson are determined as a function of the square of the dimuon invariant mass. These are the first results from this exclusive decay mode and are in agreement with a standard model prediction.

Beschreibung: Measurements are presented of differential cross sections for the production of Z bosons in association with at least one jet initiated by a charm quark in pp collisions at $$ sqrt{s} $$ s = 13 TeV. The data recorded by the CMS experiment at the LHC correspond to an integrated luminosity of 35.9 fb−1. The final states contain a pair of electrons or muons that are the decay products of a Z boson, and a jet consistent with being initiated by a charm quark produced in the hard interaction. Differential cross sections as a function of the transverse momentum pT of the Z boson and pT of the charm jet are compared with predictions from Monte Carlo event generators. The inclusive production cross section 405.4 ± 5.6 (stat) ± 24.3 (exp) ± 3.7 (theo) pb, is measured in a fiducial region requiring both leptons to have pseudorapidity |η| 10 GeV, at least one lepton with pT〉 26 GeV, and a mass of the pair in the range 71–111 GeV, while the charm jet is required to have pT〉 30 GeV and |η|