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Measurements of open charm production cross sections in deep-inelastic ep scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections for charm production are obtained in the kinematic range of photon virtuality 2.5≤ Q 2 ≤2000 GeV 2 and Bjorken scaling variable 3⋅10 −5 ≤ x ≤5⋅10 −2 . The combination method accounts for the correlations of the systematic uncertainties among the different data sets. The combined charm data together with the combined inclusive deep-inelastic scattering cross sections from HERA are used as input for a detailed NLO QCD analysis to study the influence of different heavy flavour schemes on the parton distribution functions. The optimal values of the charm mass as a parameter in these different schemes are obtained. The implications on the NLO predictions for W ± and Z production cross sections at the LHC are investigated. Using the fixed flavour number scheme, the running mass of the charm quark is determined.

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.

A bstract The production of D 0 , D * + , D + , and charm hadrons and their antiparticles in ep scattering at HERA has been studied with the ZEUS detector, using a total integrated luminosity of 372 pb −1 . The fractions of charm quarks hadronising into a particular charm hadron were derived. In addition, the ratio of neutral to charged D -meson production rates, the fraction of charged D mesons produced in a vector state, and the stangeness-suppression factor have been determined. The measurements have been performed in the photoproduction regime. The charm hadrons were reconstructed in the range of transverse momentum p T > 3 . 8 GeV and pseudorapidity | η | < 1 . 6. The charm fragmentation fractions are compared to previous results from HERA and from e + e − experiments. The data support the hypothesis that fragmentation is independent of the production process.

Abstract 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 $$137{\\,{\\text {fb}}^{-1}} $$ 137fb-1 at a center-of-mass energy of $$13\\,{\\text {TeV}} $$ 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 $$2.1\\,{\\text {TeV}} $$ 2.1TeV for gluinos and $$0.9\\,{\\text {TeV}} $$ 0.9TeV for top and bottom squarks. To facilitate reinterpretations, model-independent limits are provided in a set of simplified signal regions.

A search is presented for additional scalar (H) or pseudoscalar (A) Higgs bosons decaying to a top quark pair in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set analyzed corresponds to an integrated luminosity of 35.9 fb − 1 collected by the CMS experiment at the LHC. Final states with one or two charged leptons are considered. The invariant mass of the reconstructed top quark pair system and variables that are sensitive to the spin of the particles decaying into the top quark pair are used to search for signatures of the H or A bosons. The interference with the standard model top quark pair background is taken into account. A moderate signal-like deviation compatible with an A boson with a mass of 400 GeV is observed with a global significance of 1.9 standard deviations. New stringent constraints are reported on the strength of the coupling of the hypothetical bosons to the top quark, with the mass of the bosons ranging from 400 to 750 GeV and their total relative width from 0.5 to 25%. The results of the search are also interpreted in a minimal supersymmetric standard model scenario. Values of m A from 400 to 700 GeV are probed, and a region with values of tan β below 1.0 to 1.5, depending on m A , is excluded at 95% confidence level.

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$$ \\sqrt{s} $$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.

A search is presented for a Higgs boson that is produced in association with a Z boson and that decays to an undetected particle together with an isolated photon. The search is performed by the CMS Collaboration at the Large Hadron Collider using a data set corresponding to an integrated luminosity of 137 fb$^{-1}$ recorded at a center-of-mass energy of 13 TeV. 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 associated Higgs and Z boson production and the branching fraction for such a Higgs boson decay, as a function of the Higgs boson mass. For a mass of 125 GeV, assuming the standard model production cross section, this corresponds to an observed (expected) upper limit on this branching fraction of 4.6 (3.6)% at 95% confidence level. These are the first limits on Higgs boson decays to final states that include an undetected massless dark photon.

A search is presented for$${\\uptau }_{}^{}$$τ slepton pairs produced in proton–proton collisions at a center-of-mass energy of 13$$\\,\\text {TeV}$$TeV . The search is carried out in events containing two$${\\uptau }_{}^{}$$τ leptons in the final state, on the assumption that each$${\\uptau }_{}^{}$$τ slepton decays primarily to a$${\\uptau }_{}^{}$$τ lepton and a neutralino. Events are considered in which each$${\\uptau }_{}^{}$$τ lepton decays to one or more hadrons and a neutrino, or in which one of the$${\\uptau }_{}^{}$$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 77.2$$\\,\\text {fb}^{-1}$$fb - 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$${\\uptau }_{}^{}$$τ slepton pair production in various models for$${\\uptau }_{}^{}$$τ slepton masses between 90 and 200$$\\,\\text {GeV}$$GeV and neutralino masses of 1, 10, and 20$$\\,\\text {GeV}$$GeV . In the case of purely left-handed$${\\uptau }_{}^{}$$τ slepton production and decay to a$${\\uptau }_{}^{}$$τ lepton and a neutralino with a mass of 1$$\\,\\text {GeV}$$GeV , the strongest limit is obtained for a$${\\uptau }_{}^{}$$τ slepton mass of 125$$\\,\\text {GeV}$$GeV at a factor of 1.14 larger than the theoretical cross section.

Abstract The standard model (SM) production of four top quarks ($$\\text {t} {}{\\overline{\\text {t}}} \\text {t} {}{\\overline{\\text {t}}} $$ tt¯tt¯ ) in proton–proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016–2018 data taking of the LHC, corresponds to an integrated luminosity of 137$$\\,\\text {fb}^{-1}$$ fb-1 at a center-of-mass energy of 13$$\\,\\text {TeV}$$ TeV . The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the $$\\text {t} {}{\\overline{\\text {t}}} \\text {t} {}{\\overline{\\text {t}}} $$ tt¯tt¯ signal are respectively 2.6 and 2.7 standard deviations, and the $$\\text {t} {}{\\overline{\\text {t}}} \\text {t} {}{\\overline{\\text {t}}} $$ tt¯tt¯ cross section is measured to be $$12.6^{+5.8}_{-5.2}\\,\\text {fb} $$ 12.6-5.2+5.8fb . The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, $$y_{\\text {t}}$$ yt , yielding a limit of $$|y_{\\text {t}}/y_{\\text {t}}^{\\mathrm {SM}} | < 1.7$$ |yt/ytSM|<1.7 at $$95\\%$$ 95% confidence level, where $$y_{\\text {t}}^{\\mathrm {SM}}$$ ytSM is the SM value of $$y_{\\text {t}}$$ yt . They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework, $$\\hat{H}<0.12$$ H^<0.12 . Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350–470$$\\,\\text {GeV}$$ GeV and 350–550$$\\,\\text {GeV}$$ GeV for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.

Abstract 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 $$13\\,\\text {Te}\\text {V} $$ 13Te , collected by the CMS experiment at the LHC in 2016–2018 and corresponding to an integrated luminosity of 137$$\\,\\text {fb}^{-1}$$ 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 $$M_{\\mathrm {T2}}$$ MT2 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.