10 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

    Charge-Shifting Polycations with Tunable Rates of Hydrolysis: Effect of Backbone Substituents on Poly[2-(dimethylamino)ethyl acrylates]

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    While polycations based on 2-(dimethylamino)­ethyl methacrylate and 2-(dimethylamino)­ethyl acrylate are used in applications ranging from biomaterials to wastewater treatment, few studies have considered the remarkable differences in the hydrolytic stabilities of the respective ester groups. Here, we describe how the nature of nonmethyl α-substituents affect the rates of ester hydrolysis of such polymers, with an emphasis on the resulting shift of net polymer charge from cationic toward anionic. We introduce 2-(dimethylamino)­ethyl 2-hydroxymethyl acrylate (DHMA) as a new, very hydrolytically labile, cationic monomer that can be used to form homopolymers as well as a means to tune copolymer hydrolysis. DHMA synthesis and free radical polymerization are described, including reactivity ratios for hydroxyl-protected derivatives of DHMA and 2-(dimethylamino)­ethyl acrylate (DMAEA). Hydrolyses of PDHMA, P­[DHMA-<i>co</i>-DMAEA], PDMAEA, and PDMAEMA in pH 5 and 7 buffer are reported. The presence of the hydroxymethyl α-substituent in PDHMA led to rates of hydrolysis 2–3 orders of magnitude faster than the already rapid hydrolysis of PDMAEA. Furthermore, hydrolysis rates of P­[DHMA-<i>co</i>-DMAEA] copolymers were shown to increase as the DHMA mole fraction increased. As a result, a new route to adjusting the charge-shifting rates of such polycations in aqueous media is described

    Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La<sub>6–<i>x</i></sub>WO<sub>12–<i>y</i></sub>

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    Mixed proton–electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic–electronic conductivity. Lanthanum tungstate La<sub>6–<i>x</i></sub>WO<sub>12–<i>y</i></sub> (with <i>y</i> = 1.5<i>x</i> + δ and <i>x</i> = 0.5–0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 °C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La<sub>6–<i>x</i></sub>WO<sub>12–<i>y</i></sub> and for all substituted La<sub>6–<i>x</i></sub>WO<sub>12–<i>y</i></sub> compounds was measured in the temperature range of 400–900 °C in wet (2.5% H<sub>2</sub>O) and dry mixtures of 4% H<sub>2</sub> in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H<sub>2</sub> at 800 °C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM

    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

    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/ &lt; 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

    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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    Study of central exclusive production in proton-proton collisions at s=5.02\sqrt{s} = 5.02 and 13TeV

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    Central exclusive and semiexclusive production of pairs is measured with the CMS detector in proton-proton collisions at the LHC at center-of-mass energies of 5.02 and 13TeV. The theoretical description of these nonperturbative processes, which have not yet been measured in detail at the LHC, poses a significant challenge to models. The two pions are measured and identified in the CMS silicon tracker based on specific energy loss, whereas the absence of other particles is ensured by calorimeter information. The total and differential cross sections of exclusive and semiexclusive central production are measured as functions of invariant mass, transverse momentum, and rapidity of the system in the fiducial region defined as transverse momentum and pseudorapidity . The production cross sections for the four resonant channels , , , and are extracted using a simple model. These results represent the first measurement of this process at the LHC collision energies of 5.02 and 13TeV

    Sex Steroid Treatment of Constitutionally Tall Stature*

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