24 research outputs found

    Search for flavor-changing neutral current interactions of the top quark and the Higgs boson decaying to a bottom quark-antiquark pair at root s=13 TeV

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    A search for flavor-changing neutral current interactions of the top quark (t) and the Higgs boson (H) is presented. The search is based on a data sample corresponding to an integrated luminosity of 137 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at s√ = 13 TeV. Events containing exactly one lepton (muon or electron) and at least three jets, among which at least two are identified as originating from the hadronization of a bottom quark, are analyzed. A set of deep neural networks is used for kinematic event reconstruction, while boosted decision trees distinguish the signal from the background events. No significant excess over the background predictions is observed, and upper limits on the signal production cross sections are extracted. These limits are interpreted in terms of top quark decay branching fractions (B) to the Higgs boson and an up (u) or a charm quark (c). Assuming one nonvanishing extra coupling at a time, the observed (expected) upper limits at 95% confidence level are B(t → Hu) < 0.079 (0.11)% and B(t → Hc) < 0.094 (0.086)%

    Radiation-hardness studies of high OH- content quartz fibres irradiated with 500 MeV electrons

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    We investigated the darkening of nine high OH- fibre types irradiated with 500 MeV electrons from the Linac Injector of LEP (LIL) at CERN. The transmission of Xe light was measured in situ in the 350-800 nm range. The induced attenuation at 450 nm is typically 1.52 ± 0.15 dB/m for a 100 Mrad absorbed dose. Two-parameter fits for darkening and recovery are presented. After irradiation the tensile strength remains essentially unchanged. For Polymicro quartz core fibres the tensile strength is typically 4.6 ± 0.4 GPa. © 2002 Elsevier Science B.V. All rights reserved.DE-FG02-91ER 40664, NSF-INT-98-20258 OTKA T026184 National Council for Scientific Research TBAG-1591We thank Louis Rinolfi, Simon Baird, and the LIL operators for the delivery of a high-quality electron beam; Bernard Amacker for the connectors and fibres installation; Andre Braem for providing optical components; Minna Santaoja, Hugo Munoz, and Marc Tavlet for the dosimeter measurements; and Florence Pirotte, André Muller, and Guy Roubaud for safety controls. We also thank Thomas Ruf (LEP) and Emmanuel Tsesmelis (CMS test beam) co-ordinators. This work was supported by the US Department of Energy (DE-FG02-91ER 40664) and NSF (NSF-INT-98-20258), the Hungarian National Fund (OTKA T026184), and the Scientific and Technical Research Council of Turkey, TUBITAK, (TBAG-1591)

    Radiation-hardness studies of high OH**- content quartz fibres irradiated with 500 MeV electrons

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    We investigated the darkening of nine high OH**- fibre types irradiated with 500 MeV electrons from the Linac Injector of LEP (LIL) at CERN. The transmission of Xe light was measured in situ in the 350-800 nm range. The induced attenuation at 450 nm is typically 1.52 plus or minus 0.15 dB/m for a 100 Mrad absorbed dose. Two- parameter fits for darkening and recovery are presented. After irradiation the tensile strength remains essentially unchanged. For Polymicro quartz core fibres the tensile strength is typically 4.6 plus or minus 0.4 GPa

    P-Terphenyl Deposited Quartz Plate Calorimeter Prototype

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    IEEE Nuclear Science Symposium/Medical Imaging Conference -- OCT 19-25, 2008 -- Dresden, GERMANYWOS: 000268656000315Due to an expected increase in radiation damage under super-LHC conditions, we propose to substitute the scintillator tiles in the original design of the CMS hadronic endcap (HE) calorimeter with quartz plates. Quartz is proved to be radiation hard by various tests, but the light produced by quartz comes from Cerenkov process, and it is 100 times less than scintillation photons. To enhance the light production we treated the quartz plates with p-Terphenyl, and constructed a 20 layers calorimeter prototype. Here, we report the test beam results for hadronic and electromagnetic capabilities of the calorimeter prototype as well as radiation damage results for p-Terphenyl.IEEE Nucl & Plasma Sci Soc, Natl Nucl Secur Adm, US Def Threat Reduct Agcy, ICx Radiat GmbH, ORTEC, Hamamatsu, European Phys Journal, Hilger Crystals, SAFC Hitech, ATOMTEX, Canberra, SensL, ASP, Brookhaven Natl Lab, CEA, CERN, DESY, Forschungszentrum Julich GmbH, Int Atom Energy Agcy, Lawrence Livermore Natl La

    Energy resolution and the linearity of the CMS forward quartz fibre calorimeter pre-production-prototype (PPP-1)

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    The first pre-production-prototype (PPP-I) of the quartz fibre calorimeter of the CMS detector has been tested at CERN. The calorimeter consists of quartz fibres embedded in an iron matrix. Results are presented on the energy resolution and on the signal uniformity of the prototype for electrons and pion's and the signal uniformity and linearity

    Measurement of pseudorapidity distributions of charged particles in proton-proton collisions <tex>\sqrt{s}$</tex>=8 TeV by the CMS and TOTEM experiments

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    Evaluation of HPK n plus -p planar pixel sensors for the CMS Phase-2 upgrade

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    To cope with the challenging environment of the planned high luminosity upgrade of the Large Hadron Collider (HL-LHC), scheduled to start operation in 2029, CMS will replace its entire tracking system. The requirements for the tracker are largely determined by the long operation time of 10 years with an instantaneous peak luminosity of up to 7.5 x 1034 cm-2 s-1 in the ultimate performance scenario. Depending on the radial distance from the interaction point, the silicon sensors will receive a particle fluence corresponding to a non-ionising energy loss of up to ?eq = 3.5 x 1016 cm-2. This paper focuses on planar pixel sensor design and qualification up to a fluence of ?eq = 1.4 x 1016 cm-2. For the development of appropriate planar pixel sensors an R&amp;D program was initiated, which includes n+-p sensors on 150 mm (6") wafers with an active thickness of 150 mu m with pixel sizes of 100 x 25 mu m2 and 50 x 50 mu m2 manufactured by Hamamatsu Photonics K.K. (HPK). Single chip modules with ROC4Sens and RD53A readout chips were made. Irradiation with protons and neutrons, as well was an extensive test beam campaign at DESY were carried out. This paper presents the investigation of various assemblies mainly with ROC4Sens readout chips. It demonstrates that multiple designs fulfil the requirements in terms of breakdown voltage, leakage current and efficiency. The single point resolution for 50 x 50 mu m2 pixels is measured as 4.0 mu m for non-irradiated samples, and 6.3 mu m after irradiation to ?eq = 7.2 x 1015 cm-2

    Search for CP violating top quark couplings in pp collisions at 1as=13 TeV

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    Abstract: Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fb(-1). The search uses two observables, O-1 and O-3, which are Lorentz scalars. The observable O-1 is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while O-3 consists of the four-momenta of the charged leptons and the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model
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