1,607 research outputs found

    Development of a timing chip prototype in 110 nm CMOS technology

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    We present a readout chip prototype for future pixel detectors with timing capabilities. The prototype is intended for characterizing 4D pixel arrays with a pixel size of 100×100 μm2100\times100~\mu \text{m}^2, where the sensors are Low Gain Avalanche Diodes (LGADs). The long-term focus is towards a possible replacement of disks in the extended forward pixel system (TEPX) of the CMS experiment during the High Luminosity LHC (HL-LHC). The requirements for this ASIC are the incorporation of a Time to Digital Converter (TDC) within each pixel, low power consumption, and radiation tolerance up to 5×1015 neq cm25\times10^{15}~n_\text{eq}\text{~cm}^{-2} to withstand the radiation levels in the innermost detector modules for 3000fb13000 \text{fb}^{-1} of the HL-LHC (in the TEPX). A prototype has been designed and produced in 110~nm CMOS technology at LFoundry and UMC with different versions of TDC structures, together with a front end circuitry to interface with the sensors. The design of the TDC will be discussed, with the test set-up for the measurements, and the first results comparing the performance of the different structures

    Combination of searches for heavy resonances decaying to WW, WZ, ZZ, WH, and ZH boson pairs in proton–proton collisions at s\sqrt{s} = 8 and 13 TeV

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    A statistical combination of searches is presented for massive resonances decaying to WW, WZ, ZZ, WH, and ZH boson pairs in proton–proton collision data collected by the CMS experiment at the LHC. The data were taken at centre-of-mass energies of 8 and 13 TeV, corresponding to respective integrated luminosities of 19.7 and up to 2.7 fb1fb^{−1}. The results are interpreted in the context of heavy vector triplet and singlet models that mimic properties of composite-Higgs models predicting W′ and Z′ bosons decaying to WZ, WW, WH, and ZH bosons. A model with a bulk graviton that decays into WW and ZZ is also considered. This is the first combined search for WW, WZ, WH, and ZH resonances and yields lower limits on masses at 95% confidence level for W′ and Z′ singlets at 2.3 TeV, and for a triplet at 2.4 TeV. The limits on the production cross section of a narrow bulk graviton resonance with the curvature scale of the warped extra dimension k~=0.5\tilde{k}=0.5, in the mass range of 0.6 to 4.0 TeV, are the most stringent published to date

    The CMS trigger system

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    This paper describes the CMS trigger system and its performance during Run 1 of the LHC. The trigger system consists of two levels designed to select events of potential physics interest from a GHz (MHz) interaction rate of proton-proton (heavy ion) collisions. The first level of the trigger is implemented in hardware, and selects events containing detector signals consistent with an electron, photon, muon, τ lepton, jet, or missing transverse energy. A programmable menu of up to 128 object-based algorithms is used to select events for subsequent processing. The trigger thresholds are adjusted to the LHC instantaneous luminosity during data taking in order to restrict the output rate to 100 kHz, the upper limit imposed by the CMS readout electronics. The second level, implemented in software, further refines the purity of the output stream, selecting an average rate of 400 Hz for offline event storage. The objectives, strategy and performance of the trigger system during the LHC Run 1 are described

    Search for supersymmetry in pp collisions at s\sqrt{s} = 13 tev in the single-lepton final state using the sum of masses of large-radius jets

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    Results are reported from a search for supersymmetric particles in proton-proton collisions in the final state with a single lepton, multiple jets, including at least one b-tagged jet, and large missing transverse momentum. The search uses a sample of proton-proton collision data at s\sqrt{s} = 13 TeV recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9  fb1fb^{−1}. The observed event yields in the signal regions are consistent with those expected from standard model backgrounds. The results are interpreted in the context of simplified models of supersymmetry involving gluino pair production, with gluino decay into either on- or off-mass-shell top squarks. Assuming that the top squarks decay into a top quark plus a stable, weakly interacting neutralino, scenarios with gluino masses up to about 1.9 TeV are excluded at 95% confidence level for neutralino masses up to about 1 TeV

    Search for dark matter produced in association with heavy-flavor quark pairs in proton-proton collisions at s\sqrt{s} = 13 TeV

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    A search is presented for an excess of events with heavy-flavor quark pairs (ttt\overline{t} and bbb\overline{b}) and a large imbalance in transverse momentum in data from proton–proton collisions at a center-of-mass energy of 13TeV. The data correspond to an integrated luminosity of 2.2 fb1fb^{−1} collected with the CMS detector at the CERN LHC. No deviations are observed with respect to standard model predictions. The results are used in the first interpretation of dark matter production in ttt\overline{t} and bbb\overline{b} final states in a simplified model. This analysis is also the first to perform a statistical combination of searches for dark matter produced with different heavy-flavor final states. The combination provides exclusions that are stronger than those achieved with individual heavy-flavor final states

    Search for dark matter produced with an energetic jet or a hadronically decaying W or Z boson at s=13\sqrt{s}=13 TeV

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    A search for dark matter particles is performed using events with large missing transverse momentum, at least one energetic jet, and no leptons, in proton-proton collisions at s=13\sqrt{s}=13 TeV collected with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 12.9 fb1fb^{−1}. The search includes events with jets from the hadronic decays of a W or Z boson. The data are found to be in agreement with the predicted background contributions from standard model processes. The results are presented in terms of simplified models in which dark matter particles are produced through interactions involving a vector, axial-vector, scalar, or pseudoscalar mediator. Vector and axial-vector mediator particles with masses up to 1.95 TeV, and scalar and pseudoscalar mediator particles with masses up to 100 and 430 GeV respectively, are excluded at 95% confidence level. The results are also interpreted in terms of the invisible decays of the Higgs boson, yielding an observed (expected) 95% confidence level upper limit of 0.44 (0.56) on the corresponding branching fraction. The results of this search provide the strongest constraints on the dark matter pair production cross section through vector and axial-vector mediators at a particle collider. When compared to the direct detection experiments, the limits obtained from this search provide stronger constraints for dark matter masses less than 5, 9, and 550 GeV, assuming vector, scalar, and axial-vector mediators, respectively. The search yields stronger constraints for dark matter masses less than 200 GeV, assuming a pseudoscalar mediator, when compared to the indirect detection results from Fermi-LAT

    Search for a light pseudoscalar Higgs boson produced in association with bottom quarks in pp collisions at s\sqrt{s} = 8 TeV

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    A search for a light pseudoscalar Higgs boson (A) produced in association with bottom quarks and decaying into a muon pair is reported. The search uses 19.7 fb1fb{−1} of proton-proton collisions at a center-of-mass energy of 8 TeV, collected by the CMS experiment. No signal is observed in the dimuon mass range from 25 to 60 GeV. Upper limits on the cross section times branching fraction, σ(ppbbA)B(Aμμ)\sigma (pp \to b\overline{b}A)\mathcal{B}(A \to \mu \mu), are set

    Search for heavy gauge W' boson in events with an energetic lepton and large missing transverse momentum at s=13\sqrt{s } = 13 TeV

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    A search is presented for W′ bosons in events with an electron or muon and large missing transverse momentum, using proton–proton collision data at s=13\sqrt{s } = 13 TeV collected with the CMS detector in 2015 and corresponding to an integrated luminosity of 2.3 fb1fb^{−1}. No evidence of an excess of events relative to the standard model expectations is observed. For a W′ boson described by the sequential standard model, upper limits at 95% confidence level are set on the product of the production cross section and branching fraction and lower limits are established on the new boson mass. Masses below 4.1 TeV are excluded combining electron and muon decay channels, significantly improving upon the results obtained with the 8 TeV data. Exclusion limits at 95% confidence level on the product of the W′ production cross section and branching fraction are also derived in combination with the 8 TeV data. Finally, exclusion limits are set for the production of generic W′ bosons decaying into this final state using a model-independent approach

    Measurement of charged pion, kaon, and proton production in proton-proton collisions at s\sqrt{s} = 13 TeV

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    Transverse momentum spectra of charged pions, kaons, and protons are measured in proton-proton collisions at s\sqrt{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 pT0.11.7  GeV/cp_T \approx 0.1–1.7  GeV/c and rapidities y<1\vert y \vert < 1. The pTp_T spectra and integrated yields are compared to previous results at smaller s\sqrt{s} and to predictions of Monte Carlo event generators. The average pTp_T increases with particle mass and charged particle multiplicity of the event. Comparisons with previous CMS results at s\sqrt{s} = 0.9, 2.76, and 7 TeV show that the average pTp_T 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 black holes in high-multiplicity final states in proton-proton collisions at s=13\sqrt{s}=13 TeV

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    A search for new physics in energetic, high-multiplicity final states has been performed using proton-proton collision data collected with the CMS detector at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 2.3 fb1^{−1}. The standard model background, dominated by multijet production, is determined exclusively from control regions in data. No statistically significant excess of events is observed. Model-independent limits on the product of the cross section and the acceptance of a new physics signal in these final states are set and further interpreted in terms of limits on the production of black holes. Semiclassical black holes and string balls with masses as high as 9.5 TeV, and quantum black holes with masses as high as 9.0 TeV are excluded by this search in the context of models with extra dimensions, thus significantly extending limits set at a center-of-mass energy of 8 TeV with the LHC Run 1 data
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