920 results found
Scandale W, D'Andrea M, Esposito LS, et al., 2021, Channeling efficiency reduction in high dose neutron irradiated silicon crystals for high energy and high intensity beam collimation and extraction, Journal of Instrumentation, Vol: 16
The channeling process in bent silicon crystals are used since '70s to manipulate beams of high energy particles. During the last decade, several studies and experiments carried out by the UA9 Collaboration at CERN demonstrated the possibility to use bent crystals for beam collimation, extraction, focusing and splitting in particle accelerators. These crystals are subject to deterioration due to the interaction of the particles with the crystal lattice, degrading the beam steering performance. For this reason, robustness tests are crucial to estimate their reliability and operational lifetime. A ∼8% of reduction in channeling efficiency on crystals irradiated with 2.5•1021/cm2 thermal neutrons was measured and reported in this manuscript. Extrapolations to possible operational scenarios in high energy accelerators are also discussed.
Rossi R, Esposito LS, Garattini M, et al., 2021, Track reconstruction of particle interactions in long crystals with large bending, JOURNAL OF INSTRUMENTATION, Vol: 16, ISSN: 1748-0221
Scandale W, Cerutti F, Esposito LS, et al., 2020, The UA9 setup for the double -crystal experiment in CERN-SPS, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 975, ISSN: 0168-9002
Scandale W, Arduini G, Cerutti F, et al., 2020, Observation of strong reduction of multiple scattering for channeled particles in bent crystals, PHYSICS LETTERS B, Vol: 804, ISSN: 0370-2693
Hall G, Pesaresi M, James T, 2020, Optimisation of a silicon microstrip telescope for UA9 crystal channeling studies, Journal of Instrumentation, Vol: 15, ISSN: 1748-0221
A charged particle telescope based on silicon microstrip sensors has been used for several years for data taking at high rates in the CERN H8 beam line using a range of different incident particles. The electronic readout and data acquisition system is based on that developed for the CMS Tracker, and provides almost deadtime-free operation at trigger rates of up to about 10 kHz. The telescope was designed to characterise crystals in channeling studies by the UA9 experiment with the primary objective to validate them for use in a future LHC beam collimation system, hence is optimised for measurement of a single particle in the outgoing arm. The telescope has also been used for other studies of fundamental phenomena associated with the channeling process and further LHC applications. Some of these require a different layout of the telescope, for example to achieve a larger angular acceptance to study longer channeling crystals, or modifications to sensor operating conditions because of the very large electric charge and consequent ionisation energy loss associated with heavy ions. The telescope and its performance are described. Possible improvements are discussed.
Scandale W, Cerutti F, Esposito LS, et al., 2020, Channeling efficiency in a target-crystal assembly, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, Vol: 467, Pages: 118-122, ISSN: 0168-583X
Scandale W, Cerutti F, Esposito LS, et al., 2020, Angular asymmetry of the nuclear interaction probability of high energy particles in short bent crystals, EUROPEAN PHYSICAL JOURNAL C, Vol: 80, ISSN: 1434-6044
Abbiendi G, Bernhard J, Betti F, et al., 2020, Results on multiple Coulomb scattering from 12 and 20 GeV electrons on carbon targets, JOURNAL OF INSTRUMENTATION, Vol: 15, ISSN: 1748-0221
Scandale W, Esposito LS, Garattini M, et al., 2019, Reduction of multiple scattering of high-energy positively charged particles during channeling in single crystals, EUROPEAN PHYSICAL JOURNAL C, Vol: 79, ISSN: 1434-6044
Scandale W, Calviani M, D'Andrea M, et al., 2019, Beam steering performance of bent silicon crystals irradiated with high-intensity and high-energy protons, EUROPEAN PHYSICAL JOURNAL C, Vol: 79, ISSN: 1434-6044
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Search for a standard model-like Higgs boson in the mass range between 70 and 110 GeV in the diphoton final state in proton-proton collisions at root s=8 and 13 TeV, Physics Letters B, Vol: 793, Pages: 320-347, ISSN: 0370-2693
The results of a search for a standard model-like Higgs boson in the mass range between 70 and 110 GeV decaying into two photons are presented. The analysis uses the data set collected with the CMS experiment in proton-proton collisions during the 2012 and 2016 LHC running periods. The data sample corresponds to an integrated luminosity of 19.7 at (13) TeV. The expected and observed 95% confidence level upper limits on the product of the cross section and branching fraction into two photons are presented. The observed upper limit for the 2012 (2016) data set ranges from 129 (161) fb to 31 (26) fb. The statistical combination of the results from the analyses of the two data sets in the common mass range between 80 and 110 GeV yields an upper limit on the product of the cross section and branching fraction, normalized to that for a standard model-like Higgs boson, ranging from 0.7 to 0.2, with two notable exceptions: one in the region around the Z boson peak, where the limit rises to 1.1, which may be due to the presence of Drell–Yan dielectron production where electrons could be misidentified as isolated photons, and a second due to an observed excess with respect to the standard model prediction, which is maximal for a mass hypothesis of 95.3 GeV with a local (global) significance of 2.8 (1.3) standard deviations.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Search for invisible decays of a Higgs boson produced through vector boson fusion in proton-proton collisions at root s=13 TeV, Physics Letters B, Vol: 793, Pages: 520-551, ISSN: 0370-2693
A search for invisible decays of a Higgs boson is performed using proton-proton collision data collected with the CMS detector at the LHC in 2016 at a center-of-mass energy , corresponding to an integrated luminosity of 35.9. The search targets the production of a Higgs boson via vector boson fusion. The data are found to be in agreement with the background contributions from standard model processes. An observed (expected) upper limit of 0.33 (0.25), at 95% confidence level, is placed on the branching fraction of the Higgs boson decay to invisible particles, assuming standard model production rates and a Higgs boson mass of 125.09 GeV. Results from a combination of this analysis and other direct searches for invisible decays of the Higgs boson, performed using data collected at , 8, and 13 TeV, are presented. An observed (expected) upper limit of 0.19 (0.15), at 95% confidence level, is set on the branching fraction of invisible decays of the Higgs boson. The combined limit represents the most stringent bound on the invisible branching fraction of the Higgs boson reported to date. This result is also interpreted in the context of Higgs-portal dark matter models, in which upper bounds are placed on the spin-independent dark-matter-nucleon scattering cross section.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Search for supersymmetry in events with a photon, jets, b-jets, and missing transverse momentum in proton-proton collisions at 13TeV, European Physical Journal C: Particles and Fields, Vol: 79, ISSN: 1434-6044
A search for supersymmetry is presented based on events with at least one photon, jets, and large missing transverse momentum produced in proton–proton collisions at a center-of-mass energy of 13TeV. The data correspond to an integrated luminosity of 35.9fb−1 and were recorded at the LHC with the CMS detector in 2016. The analysis characterizes signal-like events by categorizing the data into various signal regions based on the number of jets, the number of b-tagged jets, and the missing transverse momentum. No significant excess of events is observed with respect to the expectations from standard model processes. Limits are placed on the gluino and top squark pair production cross sections using several simplified models of supersymmetric particle production with gauge-mediated supersymmetry breaking. Depending on the model and the mass of the next-to-lightest supersymmetric particle, the production of gluinos with masses as large as 2120GeV and the production of top squarks with masses as large as 1230GeV are excluded at 95% confidence level.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Combined measurements of Higgs boson couplings in proton-proton collisions at √s = 13 TeV, European Physical Journal C: Particles and Fields, Vol: 79, ISSN: 1434-6044
Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton–proton collision data set recorded with the CMS detector in 2016 at s√=13TeV, corresponding to an integrated luminosity of 35.9fb−1. The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a W or Z boson, or a top quark-antiquark pair) and the following decay modes: H→γγ, ZZ, WW, ττ, bb, and μμ. Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be μ=1.17±0.10, assuming a Higgs boson mass of 125.09GeV. Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.
Aaboud M, Aad G, Abbott B, et al., 2019, Combinations of single-top-quark production cross-section measurements and vertical bar f(LV)V(tb)vertical bar determinations at root s=7 and 8 TeV with the ATLAS and CMS experiments, Journal of High Energy Physics, Vol: 2019, ISSN: 1029-8479
This paper presents the combinations of single-top-quark production cross-section measurements by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at s√ = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb−1 at s√ = 7 TeV and 12.2 to 20.3 fb−1 at s√ = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: t-channel, tW, and s-channel. The combined t-channel cross-sections are 67.5 ± 5.7 pb and 87.7 ± 5.8 pb at s√ = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 ± 4.1 pb and 23.1 ± 3.6 pb at s√ = 7 and 8 TeV respectively. For the s-channel cross-section, the combination yields 4.9 ± 1.4 pb at s√ = 8 TeV. The square of the magnitude of the CKM matrix element Vtb multiplied by a form factor fLV is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |Vtd|, |Vts| ≪ |Vtb|. All the |fLVVtb|2 determinations, extracted from individual ratios at s√ = 7 and 8 TeV, are combined, resulting in |fLVVtb| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Search for a W ' boson decaying to a tau lepton and a neutrino in proton-proton collisions at root s=13 TeV, PHYSICS LETTERS B, Vol: 792, Pages: 107-131, ISSN: 0370-2693
A search for a new high-mass resonance decaying to a τ lepton and a neutrino is reported. The analysis uses proton-proton collision data collected by the CMS experiment at the LHC at , corresponding to an integrated luminosity of 35.9. The search utilizes hadronically decaying τ leptons. No excess in the event yield is observed at high transverse masses of the τ and missing transverse momentum. An interpretation of results within the sequential standard model excludes boson masses below 4.0 TeV at 95% confidence level. Existing limits are also improved on models in which the boson decays preferentially to fermions of the third generation. Heavy bosons with masses less than 1.7–3.9 TeV, depending on the coupling in the non-universal G(221) model, are excluded at 95% confidence level. These are the most stringent limits on this model to date.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Measurement and interpretation of differential cross sections for Higgs boson production at root s=13 TeV, Physics Letters B, Vol: 792, Pages: 369-396, ISSN: 0370-2693
Differential Higgs boson (H) production cross sections are sensitive probes for physics beyond the standard model. New physics may contribute in the gluon-gluon fusion loop, the dominant Higgs boson production mechanism at the LHC, and manifest itself through deviations from the distributions predicted by the standard model. Combined spectra for the , , and decay channels and the inclusive Higgs boson production cross section are presented, based on proton-proton collision data recorded with the CMS detector at corresponding to an integrated luminosity of 35.9. The transverse momentum spectrum is used to place limits on the Higgs boson couplings to the top, bottom, and charm quarks, as well as its direct coupling to the gluon field. No significant deviations from the standard model are observed in any differential distribution. The measured total cross section is , and the precision of the measurement of the differential cross section of the Higgs boson transverse momentum is improved by about 15% with respect to the channel alone.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Search for an Lμ - Lτ gauge boson using Z → 4μ events in proton-proton collisions at √s = 13 TeV, Physics Letters B, Vol: 792, Pages: 345-368, ISSN: 0370-2693
A search for a narrow Z gauge boson with a mass between 5 and 70 GeV resulting from an Lμ − LτU(1) local gauge symmetry is reported. Theories that predict such a particle have been proposed as anexplanation of various experimental discrepancies, including the lack of a dark matter signal in directdetection experiments, tension in the measurement of the anomalous magnetic moment of the muon,and reports of possible lepton flavor universality violation in B meson decays. A data sample of protonproton collisions at a center-of-mass energy of 13 TeV is used, corresponding to an integrated luminosityof 77.3 fb−1 recorded in 2016 and 2017 by the CMS detector at the LHC. Events containing four muonswith an invariant mass near the standard model Z boson mass are analyzed, and the selection is furtheroptimized to be sensitive to the events that may contain Z → Z μμ → 4μ decays. The event yields areconsistent with the standard model predictions. Upper limits of 10−8–10−7 at 95% confidence level areset on the product of branching fractions B(Z → Z μμ)B(Z → μμ), depending on the Z mass, whichexcludes a Z boson coupling strength to muons above 0.004–0.3. These are the first dedicated limits onLμ − Lτ models at the LHC and result in a significant increase in the excluded model parameter space.The results of this search may also be used to constrain the coupling strength of any light Z gauge bosonto muons
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Measurement of inclusive very forward jet cross sections in proton-lead collisions at p sNN=5:02 TeV, Publisher: SPRINGER
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Measurement of the energy density as a function of pseudorapidity in proton-proton collisions at root s=13 TeV, Publisher: SPRINGER
Scandale W, Arduini G, Cerutti F, et al., 2019, Focusing of 180 GeV/c pions from a point-like source into a parallel beam by a bent silicon crystal, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, Vol: 446, Pages: 15-18, ISSN: 0168-583X
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Measurement of the t(t)over-bar production cross section, the top quark mass, and the strong coupling constant using dilepton events in pp collisions at root s=13TeV, European Physical Journal C: Particles and Fields, Vol: 79, ISSN: 1434-6044
A measurement of the top quark–antiquark pair production cross section σtt¯ in proton–proton collisions at a centre-of-mass energy of 13 TeV is presented. The data correspond to an integrated luminosity of 35.9fb−1 , recorded by the CMS experiment at the CERN LHC in 2016. Dilepton events ( e ± μ ∓ , μ+μ− , e+e− ) are selected and the cross section is measured from a likelihood fit. For a top quark mass parameter in the simulation of mMCt=172.5GeV the fit yields a measured cross section σtt¯=803±2(stat)±25(syst)±20(lumi)pb , in agreement with the expectation from the standard model calculation at next-to-next-to-leading order. A simultaneous fit of the cross section and the top quark mass parameter in the powheg simulation is performed. The measured value of mMCt=172.33±0.14(stat)+0.66−0.72(syst)GeV is in good agreement with previous measurements. The resulting cross section is used, together with the theoretical prediction, to determine the top quark mass and to extract a value of the strong coupling constant with different sets of parton distribution functions.
Uchida K, Auzinger G, Belle SJ, et al., 2019, Results from the CBC3 readout ASIC for CMS 2S-modules, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol: 924, Pages: 175-180, ISSN: 0168-9002
The CBC3 is the latest version of the CMS Binary Chip for readout of the outer radial region of the upgraded CMS Tracker at the High Luminosity LHC. This 254-channel, 130 nm CMOS ASIC is designed to be bump-bonded to a substrate to which sensors will be wire-bonded. It will instrument double-layer 2S-modules, containing two overlaid silicon microstrip sensors, aligned with a parallel orientation. On-chip logic identifies Level-1 trigger primitives from high transverse-momentum tracks by selecting correlated clusters in the two sensors. The CBC3 was delivered in late 2016; wafer probing and performance tests have been carried out. Several prototype modules using the CBC3 have been produced and tested in the lab and in different beams. The results show that the CBC3 satisfies CMS requirements and only small corrections are needed for the final version of the chip for production.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Jet shapes of isolated photon-tagged jets in Pb-Pb and pp collisions at √sNN = 5.02 TeV, Physical Review Letters, Vol: 122, ISSN: 0031-9007
The modification of jet shapes in Pb-Pb collisions, relative to those in pp collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta (pT) above 1 GeV/cin annuli around the axes of jets with pjetT>30 GeV/c associated with an isolated photon with pγT>60 GeV/c. The jet shape distributions are consistent between peripheral Pb-Pb and pp collisions, but are modified for more central Pb-Pb collisions. In these central Pb-Pb events, a larger fraction of the jet momentum is observed at larger distances from the jet axis compared to pp, reflecting the interaction between the partonic medium created in heavy ion collisions and the traversing partons.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Measurements of the pp → WZ inclusive and differential production cross sections and constraints on charged anomalous triple gauge couplings at √s=13 TeV, Journal of High Energy Physics, Vol: 2019, ISSN: 1029-8479
The WZ production cross section is measured in proton-proton collisions at a centre-of-mass energy s√ = 13 TeV using data collected with the CMS detector, corresponding to an integrated luminosity of 35.9 fb−1. The inclusive cross section is measured to be σtot(pp → WZ) = 48.09 − 0.96 + 1.00 (stat) − 0.37 + 0.44 (theo) − 2.17 + 2.39 (syst) ± 1.39(lum) pb, resulting in a total uncertainty of −2.78/+2.98 pb. Fiducial cross section and ratios of charge-dependent cross section measurements are provided. Differential cross section measurements are also presented with respect to three variables: the Z boson transverse momentum pT, the leading jet pT, and the M(WZ) variable, defined as the invariant mass of the system composed of the three leptons and the missing transverse momentum. Differential measurements with respect to the W boson pT, separated by charge, are also shown. Results are consistent with standard model predictions, favouring next-to-next-to-leading-order predictions over those at next-to-leading order. Constraints on anomalous triple gauge couplings are derived via a binned maximum likelihood fit to the M(WZ) variable.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Search for contact interactions and large extra dimensions in the dilepton mass spectra from proton-proton collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 114, ISSN: 1029-8479
A search for nonresonant excesses in the invariant mass spectra of electron and muon pairs is presented. The analysis is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS experiment in 2016, corresponding to a total integrated luminosity of 36 fb−1. No significant deviation from the standard model is observed. Limits are set at 95% confidence level on energy scales for two general classes of nonresonant models. For a class of fermion contact interaction models, lower limits ranging from 20 to 32 TeV are set on the characteristic compositeness scale Λ. For the Arkani-Hamed, Dimopoulos, and Dvali model of large extra dimensions, the first results in the dilepton final state at 13 TeV are reported, and values of the ultraviolet cutoff parameter ΛT below 6.9 TeV are excluded. A combination with recent CMS diphoton results improves this exclusion to ΛT below 7.7 TeV, providing the most sensitive limits to date in nonhadronic final states.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Search for nonresonant Higgs boson pair production in the bb¯¯¯bb¯¯¯ final state at s√ = 13 TeV, The Journal of High Energy Physics, Vol: 2019, Pages: 1-49, ISSN: 1029-8479
Results of a search for nonresonant production of Higgs boson pairs, with each Higgs boson decaying to a bb¯¯¯ pair, are presented. This search uses data from proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1, collected by the CMS detector at the LHC. No signal is observed, and a 95% confidence level upper limit of 847 fb is set on the cross section for standard model nonresonant Higgs boson pair production times the squared branching fraction of the Higgs boson decay to a bb¯¯¯ pair. The same signature is studied, and upper limits are set, in the context of models of physics beyond the standard model that predict modified couplings of the Higgs boson.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Measurements of properties of the Higgs boson decaying to a W boson pair in pp collisions at √s =13 TeV, Physics Letters B, Vol: 791, Pages: 96-129, ISSN: 0370-2693
Measurements of the production of the standard model Higgs boson decaying to a W boson pair are reported. The W+W− candidates are selected in events with an oppositely charged lepton pair, large missing transverse momentum, and various numbers of jets. To select Higgs bosons produced via vector boson fusion and associated production with a W or Z boson, events with two jets or three or four leptons are also selected. The event sample corresponds to an integrated luminosity of 35.9 fb−1, collected in pp collisions at √s = 13 TeV by the CMS detector at the LHC during 2016. Combining all channels, the observed cross section times branching fraction is 1.28+0.18 −0.17 times the standard modelprediction for the Higgs boson with a mass of 125.09 GeV. This is the first observation of the Higgs boson decay to W boson pairs by the CMS experiment.
Sirunyan AM, Tumasyan A, Adam W, et al., 2019, Observation of prompt J/ψ meson elliptic flow in high-multiplicity pPb collisions at √sNN = 8.16 TeV, Physics Letters B, Vol: 791, Pages: 172-194, ISSN: 0370-2693
A measurement of the elliptic flow (v2) of prompt J/ψ mesons in high multiplicity pPb collisions is reported using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy √sNN = 8.16 TeV. Prompt J/ψ mesons decaying into two muons are reconstructed in the rapidity region in the nucleon-nucleon center-of-mass frame (ycm), corresponding to either −2.86 < ycm < −1.86 or 0.94 < ycm < 1.94. The average v2 result from the two rapidity ranges is reported over the transverse momentum (pT) range from 0.2 to 10 GeV. Positive v2 values are observed for the prompt J/ψ meson, as extracted from long-range two-particle correlations with charged hadrons, for 2 < pT < 8 GeV. The prompt J/ψ results are compared with previous CMS measurements of elliptic flow for open charm mesons (D0) and strange hadrons. From these measurements, constraints can be obtained on the collective dynamics of charm quarks produced in high-multiplicity events arising from small systems.
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