1,646 research outputs found

    Measurements of single top quark cross sections at 13 TeV with the CMS experiment

    Full text link
    An overview of recent measurements of inclusive and differential single top quark cross sections at 13 TeV with the CMS experiment is given in this note. This includes measurements targeting the tt-channel and tW production modes resulting in inclusive cross sections of \sigma_{t\mathrm{\mbox{-}ch.}}=238\pm32~\mathrm{pb} and σtW=63.1±6.6 pb\sigma_\mathrm{tW}=63.1\pm6.6~\mathrm{pb} respectively. In addition, the tt-channel cross section has been measured differentially as a function of the top quark transverse momentum and rapidity. The results are found in agreement with the standard model expectations. Furthermore, a search for single top quark production in association with a Z boson is detailed which yields an observed (expected) significance of 3.7 (3.1) standard deviations.Comment: 5 pages, 4 figures, proceedings 10th International Workshop on Top Quark Physics, Braga, Portugal, September 17-22, 201

    Measurement of Top-Quark Polarization in t-channel Single-Top Production

    Full text link
    The measurement of the top quark polarization, sensitive to the electroweak coupling structure, in t-channel single-top production is presented. Events are analyzed corresponding to an integrated luminosity of approximately 20 fb120~\mathrm{fb^{-1}} recorded with the CMS detector during pp collisions at s=8 TeV\sqrt{s}=8~\mathrm{TeV}. By requiring one isolated lepton (muon or electron), two jets, and missing transverse energy, an angular asymmetry, sensitive to the polarization of the top quark, is reconstructed in the top-quark rest frame. The corresponding angular asymmetry at parton level is inferred from data in a phase space with enhanced single-top t-channel candidates through unfolding. Remaining background contributions are estimated through a ML-fit and subtracted. A polarization of Pt=0.82±0.12 (stat.)±0.32 (syst.)P_{t}=0.82\pm0.12\mathrm{~(stat.)}\pm0.32\mathrm{~(syst.)} is measured assuming a spin-analyzing power of the charged lepton stemming from the top decay of 100%100\%.Comment: Presented at 7th International Workshop on Top Quark Physics 2014, 4 pages, 3 figure

    Observation and Modeling of the Solar-Cycle Variation of the Meridional Flow

    Get PDF
    We present independent observations of the solar-cycle variation of flows near the solar surface and at a depth of about 60 Mm, in the latitude range ±45\pm45^\circ. We show that the time-varying components of the meridional flow at these two depths have opposite sign, while the time-varying components of the zonal flow are in phase. This is in agreement with previous results. We then investigate whether the observations are consistent with a theoretical model of solar-cycle dependent meridional circulation based on a flux-transport dynamo combined with a geostrophic flow caused by increased radiative loss in the active region belt (the only existing quantitative model). We find that the model and the data are in qualitative agreement, although the amplitude of the solar-cycle variation of the meridional flow at 60 Mm is underestimated by the model.Comment: To be published in Solar Physcis Topical Issue "Helioseismology, Asteroseismology, and MHD Connections

    Формирование профилированных импульсов напряжения для время пролетного спектрометра

    Get PDF
    В работе рассматривается возможность создания время пролетного спектрометра (ВПР) с высокой разрешающей способностью. Работа прибора основана на использовании временной группировки ионов с монотонно растущей энергией, задаваемой в анализирующим элементе ВПР спектрометра. Основная задача получения профилированных импульсов ускоряющего ионы напряжения решается с использованием оригинального формирователя, с включенной параллельно нагрузке предварительно заряженной емкости задающей уровень коррекции напряжения. Проведено моделирование различных модификаций генераторов импульсов. Разработан формирователь с частичным разрядом накопительной емкости и полупроводниковым коммутаторомThe paper considers the possibility of creating a time-of-flight spectrometer with high resolution. The operation of the device is based on the use of a time grouping of ions with a monotonically increasing energy, set in the analyzing element of the spectrometer. The main task of obtaining profiled pulses of ion-accelerating voltage is solved using an original shaper, with a pre-charged capacitance connected in parallel to the load, which sets the level of voltage correction. Various modifications of pulse generators are modeled. A shaper with a partial discharge of the storage capacity and a semiconductor switch has been develope

    Data Science and Machine Learning in Education

    Full text link
    The growing role of data science (DS) and machine learning (ML) in high-energy physics (HEP) is well established and pertinent given the complex detectors, large data, sets and sophisticated analyses at the heart of HEP research. Moreover, exploiting symmetries inherent in physics data have inspired physics-informed ML as a vibrant sub-field of computer science research. HEP researchers benefit greatly from materials widely available materials for use in education, training and workforce development. They are also contributing to these materials and providing software to DS/ML-related fields. Increasingly, physics departments are offering courses at the intersection of DS, ML and physics, often using curricula developed by HEP researchers and involving open software and data used in HEP. In this white paper, we explore synergies between HEP research and DS/ML education, discuss opportunities and challenges at this intersection, and propose community activities that will be mutually beneficial.Comment: Contribution to Snowmass 202

    Transverse momentum spectra of b jets in pPb collisions at sqrt(s[NN]) = 5.02 TeV

    Get PDF
    We present a measurement of b jet transverse momentum (pt) spectra in proton-lead (pPb) collisions using a dataset corresponding to about 35 inverse nanobarns collected with the CMS detector at the LHC. Jets from b quark fragmentation are found by exploiting the long lifetime of hadrons containing a b quark through tagging methods using distributions of the secondary vertex mass and displacement. Extracted cross sections for b jets are scaled by the effective number of nucleon-nucleon collisions and are compared to a reference obtained from PYTHIA simulations of pp collisions. The PYTHIA-based estimate of the nuclear modification factor is found to be 1.22 +/- 0.15 (stat + syst pPb) +/- 0.27 (syst PYTHIA) averaged over all jets with pt between 55 and 400 GeV/c and with abs(eta[lab]) < 2. We also compare this result to predictions from models using perturbative calculations in quantum chromodynamics

    Searches for electroweak production of charginos, neutralinos, and sleptons decaying to leptons and W, Z, and Higgs bosons in pp collisions at 8 TeV

    Get PDF
    Searches for the direct electroweak production of supersymmetric charginos, neutralinos, and sleptons in a variety of signatures with leptons and W, Z, and Higgs bosons are presented. Results are based on a sample of proton-proton collision data collected at center-of-mass energy sqrt(s) = 8 TeV with the CMS detector in 2012, corresponding to an integrated luminosity of 19.5 inverse femtobarns. The observed event rates are in agreement with expectations from the standard model. These results probe charginos and neutralinos with masses up to 720 GeV, and sleptons up to 260 GeV, depending on the model details

    Search for quark contact interactions and extra spatial dimensions using dijet angular distributions in proton-proton collisions at sqrt(s) = 8 TeV

    Get PDF
    A search is presented for quark contact interactions and extra spatial dimensions in proton-proton collisions at sqrt(s) = 8 TeV using dijet angular distributions. The search is based on a data set corresponding to an integrated luminosity of 19.7 inverse femtobarns collected by the CMS detector at the CERN LHC. Dijet angular distributions are found to be in agreement with the perturbative QCD predictions that include electroweak corrections. Limits on the contact interaction scale from a variety of models at next-to-leading order in QCD corrections are obtained. A benchmark model in which only left-handed quarks participate is excluded up to a scale of 9.0 (11.7) TeV for destructive (constructive) interference at 95% confidence level. Lower limits between 5.9 and 8.4 TeV on the scale of virtual graviton exchange are extracted for the Arkani-Hamed--Dimopoulos--Dvali model of extra spatial dimensions

    Search for the associated production of the Higgs boson with a top-quark pair

    Get PDF
    A search for the standard model Higgs boson produced in association with a top-quark pair (t tbar H) is presented, using data samples corresponding to integrated luminosities of up to 5.1 inverse femtobarns and 19.7 inverse femtobarns collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H to hadrons, H to photons, and H to leptons. The results are characterized by an observed t tbar H signal strength relative to the standard model cross section, mu = sigma/sigma[SM], under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is mu = 2.8 +/- 1.0 for a Higgs boson mass of 125.6 GeV
    corecore