Engineering topics

Vannerom, David

Publications and source records attributed to Vannerom, David.

263 records · Page 15

DOE OSTI2017

A search for new phenomena in pp collisions at $\sqrt{s} = 13\,\text {TeV} $ in final states with missing transverse momentum and at least one jet using the $\alpha _{\mathrm {T}}$ variable

A search for new phenomena is performed in final states containing one or more jets and an imbalance in transverse momentum in pp collisions at a centre-of-mass energy of 13 $\,\text {TeV}$ . The analysed data sample, recorded with the CMS detector at the CERN LHC, corresponds to an integrated luminosity of 2.3 $\,\text {fb}^{-1}$ . Several kinematic variables are employed to suppress the dominant background, multijet production, as well as to discriminate between other standard model and new physics processes. The search provides sensitivity to a broad range of new-physics models that yield a stable weakly interacting massive particle. The number of observed candidate events is found to agree with the expected contributions from standard model processes, and the result is interpreted in the mass parameter space of fourteen simplified supersymmetric models that assume the pair production of gluinos or squarks and a range of decay modes. For models that assume gluino pair production, masses up to 1575 and 975 $\,\text {GeV}$ are excluded for gluinos and neutralinos, respectively. For models involving the pair production of top squarks and compressed mass spectra, top squark masses up to 400 $\,\text {GeV}$ are excluded.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for single production of vector-like quarks decaying to a Z boson and a top or a bottom quark in proton-proton collisions at $ \sqrt{s}=13 $ TeV

A search for single production of vector-like quarks, T and B, decaying into a Z boson and a top or a bottom quark, respectively, is presented. The search is performed using data collected by the CMS experiment at the LHC in proton-proton collisions at $ \sqrt{s}=13 $ TeV, corresponding to an integrated luminosity of 2.3fb$^{−1}$. An exotic T quark production mode through the decay of a heavy Z′ resonance is also considered. The search is performed in events with a Z boson decaying leptonically, accompanied by a bottom or a top quark decaying hadronically. No excess of events is observed over the standard model background expectation. Products of production cross section and branching fraction for T and B quarks from 1.26 and 0.13 pb are excluded at 95% confidence level for the range of resonance mass considered, which is between 0.7 and 1.7 TeV. Limits on the product of the Z′ boson production cross section and branching fraction, with the Z′ boson decaying to the Tt final state, are set between 0.31 and 0.13 pb, for Z′ boson masses in the range from 1.5 to 2.5 TeV. This is the first search at 13 TeV for single production of vector-like quarks in events with a Z boson decaying leptonically accompanied by boosted jets.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of prompt and nonprompt $\mathrm{J}/{\psi }$ production in $\mathrm {p}\mathrm {p}$ and $\mathrm {p}\mathrm {Pb}$ collisions at $\sqrt{s_{\mathrm {NN}}} =5.02\,\text {TeV} $

This paper reports the measurement of $\mathrm{J}/{\psi }$ meson production in proton–proton ( $\mathrm {p}\mathrm {p}$ ) and proton–lead ( $\mathrm {p}\mathrm {Pb}$ ) collisions at a center-of-mass energy per nucleon pair of $5.02\,\text {TeV} $ by the CMS experiment at the LHC. The data samples used in the analysis correspond to integrated luminosities of 28 $\,\text {pb}^{-1}$ and 35 $\,\text {nb}^{-1}$ for $\mathrm {p}\mathrm {p}$ and $\mathrm {p}\mathrm {Pb}$ collisions, respectively. Prompt and nonprompt $\mathrm{J}/{\psi }$ mesons, the latter produced in the decay of ${\mathrm {B}}$ hadrons, are measured in their dimuon decay channels. Differential cross sections are measured in the transverse momentum range of $2

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for electroweak production of a vector-like quark decaying to a top quark and a Higgs boson using boosted topologies in fully hadronic final states

A search is performed for electroweak production of a vector-like top quark partner T of charge 2/3 in association with a standard model top or bottom quark, using 2.3 fb$^{−1}$ of proton-proton collision data at $ \sqrt{s}=13 $ TeV collected by the CMS experiment at the CERN LHC. The search targets T quarks decaying to a top quark and a Higgs boson in fully hadronic final states. For a T quark with mass above 1 TeV the daughter top quark and Higgs boson are highly Lorentz-boosted and can each appear as a single hadronic jet. Jet substructure and b tagging techniques are used to identify the top quark and Higgs boson jets, and to suppress the standard model backgrounds. An excess of events is searched for in the T quark candidate mass distribution in the data, which is found to be consistent with the expected backgrounds. Upper limits at 95% confidence level are set on the product of the single T quark production cross sections and the branching fraction $ \mathrm{\mathcal{B}}\left(\mathrm{T}\to \mathrm{t}\mathrm{H}\right) $ , and these vary between 0.31 and 0.93 pb for T quark masses in the range 1000-1800 GeV. This is the first search for single electroweak production of a vector-like T quark in fully hadronic final states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Mechanical stability of the CMS strip tracker measured with a laser alignment system

The CMS tracker consists of 206 m(2) of silicon strip sensors assembled on carbon fibre composite structures and is designed for operation in the temperature range from −25 to +25°C. The mechanical stability of tracker components during physics operation was monitored with a few μm resolution using a dedicated laser alignment system as well as particle tracks from cosmic rays and hadron-hadron collisions. During the LHC operational period of 2011–2013 at stable temperatures, the components of the tracker were observed to experience relative movements of less than 30μm. In addition, temperature variations were found to cause displacements of tracker structures of about 2μm°C, which largely revert to their initial positions when the temperature is restored to its original value.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2017

Suppression and azimuthal anisotropy of prompt and nonprompt ${\mathrm{J}}/\psi $ production in PbPb collisions at $\sqrt{{s_{_{\text {NN}}}}} =2.76$ $\,\mathrm{TeV}$

The nuclear modification factor $R_{\mathrm{AA}}$ and the azimuthal anisotropy coefficient $v_{2}$ of prompt and nonprompt (i.e. those from decays of b hadrons) ${\mathrm{J}}/\psi $ mesons, measured from PbPb and pp collisions at $\sqrt{{s_{_{\text {NN}}}}} =2.76$ $\,\mathrm{TeV}$ at the LHC, are reported. The results are presented in several event centrality intervals and several kinematic regions, for transverse momenta $p_{\mathrm{T}} >6.5$ $\,{\mathrm{GeV}}/{\mathrm{c}}$ and rapidity $|{y}|<2.4$ , extending down to $p_{\mathrm{T}} =3$ $\,{\mathrm{GeV}}/{\mathrm{c}}$ in the $1.6<|{y}|<2.4$ range. The $v_{2}$ of prompt ${\mathrm{J}}/\psi $ is found to be nonzero, but with no strong dependence on centrality, rapidity, or $p_{\mathrm{T}}$ over the full kinematic range studied. The measured $v_{2}$ of nonprompt ${\mathrm{J}}/\psi $ is consistent with zero. The $R_{\mathrm{AA}}$ of prompt ${\mathrm{J}}/\psi $ exhibits a suppression that increases from peripheral to central collisions but does not vary strongly as a function of either y or $p_{\mathrm{T}}$ in the fiducial range. The nonprompt ${\mathrm{J}}/\psi $ $R_{\mathrm{AA}}$ shows a suppression which becomes stronger as rapidity or $p_{\mathrm{T}}$ increases. The $v_{2}$ and $R_{\mathrm{AA}}$ of open and hidden charm, and of open charm and beauty, are compared.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Charged-particle nuclear modification factors in PbPb and pPb collisions at $ \sqrt{s_{\mathrm{N}\;\mathrm{N}}}=5.02 $ TeV

The spectra of charged particles produced within the pseudorapidity window |η| < 1 at $ \sqrt{s_{\mathrm{N}\,\mathrm{N}}}=5.02 $ TeV are measured using 404 μb$^{−1}$ of PbPb and 27.4 pb$^{−1}$ of pp data collected by the CMS detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0.5 < p$_{T}$ < 400 GeV in pp and 0.7 < p$_{T}$ < 400 GeV in PbPb collisions. The corresponding nuclear modification factor, R$_{AA}$, is measured in bins of collision centrality. The R$_{AA}$ in the 5% most central collisions shows a maximal suppression by a factor of 7-8 in the p$_{T}$ region of 6-9 GeV. This dip is followed by an increase, which continues up to the highest p$_{T}$ measured, and approaches unity in the vicinity of p$_{T}$ = 200 GeV. The R$_{AA}$ is compared to theoretical predictions and earlier experimental results at lower collision energies. The newly measured pp spectrum is combined with the pPb spectrum previously published by the CMS collaboration to construct the pPb nuclear modification factor, R$_{pA}$, up to 120 GeV. For p$_{T}$ > 20 GeV, R$_{pA}$ exhibits weak momentum dependence and shows a moderate enhancement above unity.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Search for massive resonances decaying into WW, WZ or ZZ bosons in proton-proton collisions at $\sqrt{s} = $ 13 TeV

A search is presented for new massive resonances decaying to WW, WZ or ZZ bosons in $ \ell \nu q\overline{q} $ and $ q\overline{q}q\overline{q} $ final states. Results are based on data corresponding to an integrated luminosity of 2.3-2.7 fb$^{−1}$ recorded in proton-proton collisions at $ \sqrt{s}=13 $ TeV with the CMS detector at the LHC. Decays of spin-1 and spin-2 resonances into two vector bosons are sought in the mass range 0.6-4.0 TeV. No significant excess over the standard model background is observed. Combining the results of the $ \ell \nu q\overline{q} $ and $ q\overline{q}q\overline{q} $ final states, cross section and mass exclusion limits are set for models that predict heavy spin-1 and spin-2 resonances. This is the first search for a narrow-width spin-2 resonance at $ \sqrt{s}=13 $ TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for CP violation in $ t\overline{t} $ production and decay in proton-proton collisions at $ \sqrt{s}=8 $ TeV

The results of a first search for CP violation in the production and decay of top quark-antiquark ( $ t\overline{t} $ ) pairs are presented. The search is based on asymmetries in T-odd, triple-product correlation observables, where T is the time-reversal operator. The analysis uses a sample of proton-proton collisions at $ \sqrt{s}=8 $ TeV collected by the CMS experiment, corresponding to an integrated luminosity of 19.7 fb$^{−1}$. Events are selected having one electron or muon and at least four jets. The T-odd observables are measured using four-momentum vectors associated with $ t\overline{t} $ production and decay. The measured asymmetries exhibit no evidence for CP-violating effects, consistent with the expectation from the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for heavy neutrinos or third-generation leptoquarks in final states with two hadronically decaying $\tau$ leptons and two jets in proton-proton collisions at $ \sqrt{s}=13 $ TeV

A search for new particles has been conducted using events with two high transverse momentum (p$_{T}$) τ leptons that decay hadronically, at least two high-p$_{T}$ jets, and missing transverse energy from the τ lepton decays. The analysis is performed using data from proton-proton collisions, collected by the CMS experiment in 2015 at $ \sqrt{s}=13 $ TeV, corresponding to an integrated luminosity of 2.1 fb$^{−1}$. The results are interpreted in two physics models. The first model involves heavy right-handed neutrinos, N$_{ℓ}$ (ℓ = e, μ, τ), and right-handed charged bosons, W$_{R}$, arising in a left-right symmetric extension of the standard model. Masses of the W$_{R}$ boson below 2.35 (1.63) TeV are excluded at 95% confidence level, assuming the N$_{τ}$ mass is 0.8 (0.2) times the mass of the W$_{R}$ boson and that only the N$_{τ}$ flavor contributes to the W$_{R}$ decay width. In the second model, pair production of third-generation scalar leptoquarks that decay into ττbb is considered. Third-generation scalar leptoquarks with masses below 740 GeV are excluded, assuming a 100% branching fraction for the leptoquark decay to a τ lepton and a bottom quark. This is the first search at hadron colliders for the third-generation Majorana neutrino, as well as the first search for third-generation leptoquarks in the final state with a pair of hadronically decaying τ leptons and jets.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for dark matter and unparticles in events with a Z boson and missing transverse momentum in proton-proton collisions at $ \sqrt{s}=13 $ TeV

A search for dark matter and unparticle production at the LHC has been performed using events containing two charged leptons (electrons or muons), consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 fb$^{−1}$ of proton-proton collisions at the LHC, at a center-of-mass energy of 13 TeV. No excess over the standard model expectation is observed. Compared to previous searches in this topology, which exclusively relied on effective field theories, the results are interpreted in terms of a simplified model of dark matter production for both vector and axial vector couplings between a mediator and dark matter particles. The first study of this class of models using CMS data at $ \sqrt{s}=13 $ TeV is presented. Additionally, effective field theories of dark matter and unparticle production are used to interpret the data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗