11 research outputs found

    Search for pair-produced resonances decaying to quark pairs in proton-proton collisions at root s=13 TeV

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    A general search for the pair production of resonances, each decaying to two quarks, is reported. The search is conducted separately for heavier resonances (masses above 400 GeV), where each of the four final-state quarks generates a hadronic jet resulting in a four-jet signature, and for lighter resonances (masses between 80 and 400 GeV), where the pair of quarks from each resonance is collimated and reconstructed as a single jet resulting in a two-jet signature. In addition, a b-tagged selection is applied to target resonances with a bottom quark in the final state. The analysis uses data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 35.9 fb(-1), from proton-proton collisions at a center-of-mass energy of 13 TeV. The mass spectra are analyzed for the presence of new resonances, and are found to be consistent with standard model expectations. The results are interpreted in the framework of R-parity-violating supersymmetry assuming the pair production of scalar top quarks decaying via the hadronic coupling lambda ''(312) or lambda ''(323) and upper limits on the cross section as a function of the top squark mass are set. These results probe a wider range of masses than previously explored at the LHC, and extend the top squark mass limits in the (t) over tilde -> qq' scenario.Peer reviewe

    Measurement of charged pion, kaon, and proton production in proton-proton collisions at root s=13 TeV

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    Transverse momentum spectra of charged pions, kaons, and protons are measured in proton-proton collisions at √s = 13 TeV with the CMS detector at the LHC. The particles, identified via their energy loss in the silicon tracker, are measured in the transverse momentum range of pT ∼ 0.1-1.7 GeV/c and rapidities /y/ < 1. The pT spectra and integrated yields are compared to previous results at smaller √s and to predictions of Monte Carlo event generators. The average pT increases with particle mass and charged particle multiplicity of the event. Comparisons with previous CMS results at √s = 0.9, 2.76, and 7 TeV show that the average pT and the ratios of hadron yields feature very similar dependences on the particle multiplicity in the event, independently of the center-of-mass energy of the pp collision

    Measurement of ttˉ\hbox {t}{\bar{\hbox {t}}} normalised multi-differential cross sections in pp{\text {p}}{\text {p}} collisions at s=13TeV\sqrt{s}=13\,{\text {TeV}} , and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

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    Normalised multi-differential cross sections for top quark pair (ttˉ\hbox {t}{\bar{\hbox {t}}}) production are measured in proton-proton collisions at a centre-of-mass energy of 13TeV\,{\text {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 35.9fb135.9{\,{\text {fb}}^{-1}} . The double-differential ttˉ\hbox {t}{\bar{\hbox {t}}} cross section is measured as a function of the kinematic properties of the top quark and of the ttˉ\hbox {t}{\bar{\hbox {t}}} 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 ttˉ\hbox {t}{\bar{\hbox {t}}} 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 αS\alpha _{S} and the top quark pole mass (mtpolem_{{\text {t}}}^{{\text {pole}}}) using several sets of parton distribution functions (PDFs). The measurement of mtpolem_{{\text {t}}}^{{\text {pole}}} exploits the sensitivity of the ttˉ\hbox {t}{\bar{\hbox {t}}} invariant mass distribution to mtpolem_{{\text {t}}}^{{\text {pole}}} near the production threshold. Furthermore, a simultaneous fit of the PDFs, αS\alpha _{S}, and mtpolem_{{\text {t}}}^{{\text {pole}}} 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 αS\alpha _{S} and mtpolem_{{\text {t}}}^{{\text {pole}}}. The values αS(mZ)=0.11350.0017+0.0021\alpha _{S}(m_{{\text {Z}}}) = 0.1135{}^{+0.0021}_{-0.0017} and mtpole=170.5±0.8GeVm_{{\text {t}}}^{{\text {pole}}} = 170.5 \pm 0.8 \,{\text {GeV}} 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 ttˉ\hbox {t}{\bar{\hbox {t}}} production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of mtpolem_{{\text {t}}}^{{\text {pole}}} of the order of +1GeV+1 \,{\text {GeV}} , which can be regarded as additional theoretical uncertainty in the current mtpolem_{{\text {t}}}^{{\text {pole}}} extraction

    Observation of nuclear modifications in W± boson production in pPb collisions at sNN=8.16TeV

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    The production of W± bosons is studied in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of sNN=8.16TeV. Measurements are performed in the W±→μ±νμ channel using a data sample corresponding to an integrated luminosity of 173.4±6.1nb−1, collected by the CMS Collaboration at the LHC. The number of positively and negatively charged W bosons is determined separately in the muon pseudorapidity region in the laboratory frame |ηlabμ|25GeV/c. The W± boson differential cross sections, muon charge asymmetry, and the ratios of W± boson yields for the proton-going over the Pb-going beam directions are reported as a function of the muon pseudorapidity in the nucleon-nucleon centre-of-mass frame. The measurements are compared to the predictions from theoretical calculations based on parton distribution functions (PDFs) at next-to-leading-order. The results favour PDF calculations that include nuclear modifications and provide constraints on the nuclear PDF global fits

    Search for an excited lepton that decays via a contact interaction to a lepton and two jets in proton-proton collisions at s \sqrt{s} = 13 TeV

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    Results are presented from a search for events containing an excited lepton (electron or muon) produced in association with an ordinary lepton of the same flavor and decaying to a lepton and two hadronic jets. Both the production and the decay of the excited leptons are assumed to occur via a contact interaction with a characteristic energy scale Λ. The branching fraction for the decay mode under study increases with the mass of the excited lepton and is the most sensitive channel for very heavy excited leptons. The analysis uses a sample of proton-proton collisions collected by the CMS experiment at the LHC at s \sqrt{s} = 13 TeV, corresponding to an integrated luminosity of 77.4 fb−1. The four-body invariant mass of the two lepton plus two jet system is used as the primary discriminating variable. No significant excess of events beyond the expectation for standard model processes is observed. Assuming that Λ is equal to the mass of the excited leptons, excited electrons and muons with masses below 5.6 and 5.7 TeV, respectively, are excluded at 95% confidence level. These are the best limits to date

    Search for low mass vector resonances decaying into quark-antiquark pairs in proton-proton collisions at s=13  TeV\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}

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