1,457 research outputs found

    Search for the standard model deviations in top quark precision studies at CMS

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    Precision studies of top quark properties provide a unique playground to test the predictions of the standard model and to search for new physics. Reviewed results from the CMS experiment done with the data collected at 8 TeV include studies of top quark Wtb anomalous and FCNC couplings, polarization, CP-violation, and spin correlation effects. No significant deviations from the SM predictions are observed.Comment: Presented at 29th Rencontres de Blois (Blois 2017), Blois, Franc

    Rare top quark production and decays at ATLAS and CMS

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    The most recent studies in the top quark sector are reviewed with the focus on the rare production mechanisms and suppressed decays. The experimental results obtained with the ATLAS and CMS detectors in proton-proton collisions at the center-of-mass energy of 13 TeV include the measurements of the associated production of top quark pairs with vector bosons (ttˉW{\rm t\bar{t}W}, ttˉZ{\rm t\bar{t}Z}, ttˉγ{\rm t\bar{t}\gamma}), the first evidence for the t(tˉ)γq{\rm t(\bar{t})\gamma q} process, the first observation of the t(tˉ)Zq{\rm t(\bar{t})Zq} production, the study of the ttˉ+bbˉ{\rm t\bar{t}+b\bar{b}} and ttˉ+ttˉ{\rm t\bar{t}+t\bar{t}} processes, as well as searches for lepton flavour violation in top quark decays and effective field theory interpretations. The experimental results show good agreement with the theoretical predictions.Comment: Presented at the 2019 EW session of the 54th Rencontres de Moriond, La Thuile, Ital

    Search for flavour-changing neutral currents with top quarks

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    Flavour-changing neutral currents are extremely rare processes in the standard model that can be sensitive to various new physics effects. The summary of the latest experimental results from the LHC experiments is given. Preliminary results of sensitivity studies for future colliders are also discussed.Comment: Presented at 10th International Workshop on Top Quark Physics 2017 (TOP 2017), Braga, Portuga

    Particles in a pocket

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    Communicating science through mobile smartphone and tablet applications is one of the most efficient ways to reach general public of diverse background and age coverage. The Higgsy project was created in 2022 to celebrate the 10th anniversary of the discovery of the Higgs boson at CERN. This project introduces a mobile game to search for the Higgs boson production in a generic particle detector. The MatterBricks is an augmented-reality project that was created for a major national event in Belgium, held in 2023. The main features of the two mobile applications and further prospects for reaching general public through mobile application development process are discussed.Comment: Presented at the European Physical Society Conference on High Energy Physics (EPS-HEP) 2023, Hamburg, German

    Flavour-changing neutral scalar interactions of the Top Quark

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    A study of the top-quark interactions via flavour-changing neutral current (FCNC) processes provides an intriguing connection between the heaviest elementary particle of the standard model (SM) of particle physics and the new scalar bosons that are predicted in several notable SM extensions. The production cross sections of the processes with top-scalar FCNC interactions can be significantly enhanced to the observable level at the CERN Large Hadron Collider. The present review summarises the latest experimental results on the study of the top-quark interactions with the Higgs boson via an FCNC and describes several promising directions to look for new scalar particles.NC is supported by the FCT—Fundação para a CiĂȘncias e a Tecnologia, Portugal, under project CERN/FIS-PAR/0032/2021

    Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV

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    Many measurements and searches for physics beyond the standard model at the LHC rely on the efficient identification of heavy-flavour jets, i.e. jets originating from bottom or charm quarks. In this paper, the discriminating variables and the algorithms used for heavy-flavour jet identification during the first years of operation of the CMS experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, are presented. Heavy-flavour jet identification algorithms have been improved compared to those used previously at centre-of-mass energies of 7 and 8 TeV. For jets with transverse momenta in the range expected in simulated tt‟\mathrm{t}\overline{\mathrm{t}} events, these new developments result in an efficiency of 68% for the correct identification of a b jet for a probability of 1% of misidentifying a light-flavour jet. The improvement in relative efficiency at this misidentification probability is about 15%, compared to previous CMS algorithms. In addition, for the first time algorithms have been developed to identify jets containing two b hadrons in Lorentz-boosted event topologies, as well as to tag c jets. The large data sample recorded in 2016 at a centre-of-mass energy of 13 TeV has also allowed the development of new methods to measure the efficiency and misidentification probability of heavy-flavour jet identification algorithms. The heavy-flavour jet identification efficiency is measured with a precision of a few per cent at moderate jet transverse momenta (between 30 and 300 GeV) and about 5% at the highest jet transverse momenta (between 500 and 1000 GeV)

    Particle-flow reconstruction and global event description with the CMS detector

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    The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS performance for jet and hadronic tau decay reconstruction, missing transverse momentum determination, and electron and muon identification. This approach also allows particles from pileup interactions to be identified and enables efficient pileup mitigation methods. The data collected by CMS at a centre-of-mass energy of 8 TeV show excellent agreement with the simulation and confirm the superior PF performance at least up to an average of 20 pileup interactions

    Search for heavy resonances decaying to a top quark and a bottom quark in the lepton+jets final state in proton–proton collisions at 13 TeV

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