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Bruno, G.

Publications and source records attributed to Bruno, G..

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

In-situ pore size investigations of loaded porous concrete with non-destructive methods

Subject of this investigation is the in-situ evolution of pore volume and pore size distribution in Ytong (a porous concrete material) under increasing pressure with two different non-destructive analytical methods: Nuclear Magnetic Resonance (NMR) and X-ray Computed Tomography (CT). For both methods special strain devices to apply external pressure were constructed. The results from the two techniques yield complementary information on the pore size distribution and allows covering different pore size regions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Search for top squarks decaying via four-body or chargino-mediated modes in single-lepton final states in proton-proton collisions at $ \sqrt{s}=13 $ TeV

Here, a search for the pair production of the lightest supersymmetric partner of the top quark ($\widetilde{\mathrm{t}}_1$) is presented. The search focuses on a compressed scenario where the mass difference between the top squark and the lightest supersymmetric particle, often considered to be the lightest neutralino ($\widetilde{\chi}^0_1$), is smaller than the mass of the W boson. The proton-proton collision data were recorded by the CMS experiment at a centre-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 35.9 fb$^{-1}$. In this search, two decay modes of the top squark are considered: a four-body decay into a bottom quark, two additional fermions, and a $\widetilde{\chi}^0_1$; and a decay via an intermediate chargino. Events are selected using the presence of a high-momentum jet, significant missing transverse momentum, and a low transverse momentum electron or muon. Two analysis techniques are used, targeting different decay modes of the $\widetilde{\mathrm{t}}_1$: a sequential selection and a multivariate technique. No evidence for the production of top squarks is found, and mass limits at 95% confidence level are set that reach up to 560 GeV, depending on the $m(\widetilde{\mathrm{t}}_1) - m(\widetilde{\chi}^0_1)$ mass difference and the decay mode.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for dark matter produced in association with a Higgs boson decaying to γγ or τ + τ – at $ \sqrt{s}=13 $ TeV

A search for dark matter particles is performed by looking for events with large transverse momentum imbalance and a recoiling Higgs boson decaying to either a pair of photons or a pair of τ leptons. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV collected at the CERN LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No significant excess over the expected standard model background is observed. Upper limits at 95% confidence level are presented for the product of the production cross section and branching fraction in the context of two benchmark simplified models. For the Z$^{'}$-two-Higgs-doublet model (where Z$^{'}$ is a new massive boson mediator) with an intermediate heavy pseudoscalar particle of mass m$_{A}$ = 300 GeV and m$_{DM}$ = 100 GeV, the Z$^{'}$ masses from 550 GeV to 1265 GeV are excluded. For a baryonic Z$^{'}$ model, with m$_{DM}$ = 1 GeV, Z$^{'}$ masses up to 615 GeV are excluded. Results are also presented for the spin-independent cross section for the dark matter-nucleon interaction as a function of the mass of the dark matter particle. In conclusion, this is the first search for dark matter particles produced in association with a Higgs boson decaying to two τ leptons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of the weak mixing angle using the forward–backward asymmetry of Drell–Yan events in $\mathrm {p}\mathrm {p}$ collisions at 8$\,\text {TeV}$

Here, a measurement is presented of the effective leptonic weak mixing angle ($\sin^2\theta^{\ell}_{\text{eff}}$) using the forward-backward asymmetry of Drell-Yan lepton pairs ($\mu\mu$ and ee) produced in proton-proton collisions at $\sqrt{s}=$ 8 TeV at the CMS experiment of the LHC. The data correspond to integrated luminosities of 18.8 and 19.6 fb$^{-1}$ in the dimuon and dielectron channels, respectively, containing 8.2 million dimuon and 4.9 million dielectron events. With more events and new analysis techniques, including constraints obtained on the parton distribution functions from the measured forward-backward asymmetry, the statistical and systematic uncertainties are significantly reduced relative to previous CMS measurements. The extracted value of $\sin^2\theta^{\ell}_{\text{eff}}$ from the combined dilepton data is $\sin^2\theta^{\ell}_{\text{eff}} =$ 0.23101 $\pm$ 0.00036 (stat) $\pm$ 0.00018 (syst) $\pm$ 0.00016 (theo) $\pm$ 0.00031 (parton distributions in proton) = 0.23101 $\pm$ 0.00053.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurement of charged particle spectra in minimum-bias events from proton–proton collisions at $\sqrt{s}=13\,\text {TeV} $

Pseudorapidity, transverse momentum, and multiplicity distributions are measured in the pseudorapidity range $|\eta | < 2.4$ for charged particles with transverse momenta satisfying $p_{\mathrm {T}} > 0.5\,\text {GeV} $ in proton–proton collisions at a center-of-mass energy of $\sqrt{s} = 13\,\text {TeV} $ . Measurements are presented in three different event categories. The most inclusive of the categories corresponds to an inelastic $\mathrm {p}$ $\mathrm {p}$ data set, while the other two categories are exclusive subsets of the inelastic sample that are either enhanced or depleted in single diffractive dissociation events. As a result, the measurements are compared to predictions from Monte Carlo event generators used to describe high-energy hadronic interactions in collider and cosmic-ray physics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Observation of the χ b 1 ( 3 P ) and χ b 2 ( 3 P ) and Measurement of their Masses

The $\chi_\mathrm{b1}$(3P) and $\chi_\mathrm{b2}$(3P) states are observed through their $\Upsilon$(3S) $\gamma$ decays, using an event sample of proton-proton collisions collected by the CMS experiment at the CERN LHC. The data were collected at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 80.0 fb$^{-1}$. The $\Upsilon$(3S) mesons are identified through their dimuon decay channel, while the low-energy photons are detected after converting to e$^+$e$^-$ pairs in the silicon tracker, leading to a $\chi_\mathrm{b}$(3P) mass resolution of 2.2 MeV. This is the first time that the $J =$ 1 and 2 states are well resolved and their masses individually measured: 10$\,$513.42 $\pm$ 0.41 (stat) $\pm$ 0.18 (syst) MeV and 10$\,$524.02 $\pm$ 0.57 (stat) $\pm$ 0.18 (syst) MeV; they are determined with respect to the world-average value of the $\Upsilon$(3S) mass, which has an uncertainty of 0.5 MeV. As a result, the mass splitting is measured to be 10.60 $\pm$ 0.64 (stat) $\pm$ 0.17 (syst) MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for vector-like T and B quark pairs in final states with leptons at $ \sqrt{s}=13 $ TeV

A search is presented for pair production of heavy vector-like T and B quarks in proton-proton collisions at $\sqrt{s} =$ 13 TeV. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$, collected with the CMS detector at the CERN LHC in 2016. Pair production of T quarks would result in a wide range of final states, since vector-like T quarks of charge 2$e$/3 are predicted to decay to bW, tZ, and tH. Likewise, vector-like B quarks are predicted to decay to tW, bZ, and bH. Three channels are considered, corresponding to final states with a single lepton, two leptons with the same sign of the electric charge, or at least three leptons. The results exclude T quarks with masses below 1140-1300 GeV and B quarks with masses below 910-1240 GeV for various branching fraction combinations, extending the reach of previous CMS searches by 200-600 GeV. These are the strongest exclusion limits to date for T quarks with a branching fraction to tZ greater than ${\approx}$0.5 and for B quarks with a branching fraction to tW less than ${\approx}$0.6.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for beyond the standard model Higgs bosons decaying into a $ \mathrm{b}\overline{\mathrm{b}} $ pair in pp collisions at $ \sqrt{s}=13 $ TeV

A search for Higgs bosons that decay into a bottom quark-antiquark pair and are accompanied by at least one additional bottom quark is performed with the CMS detector. The data analyzed were recorded in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} =$ 13 TeV at the LHC, corresponding to an integrated luminosity of 35.7 fb$^{-1}$. The final state considered in this analysis is particularly sensitive to signatures of a Higgs sector beyond the standard model, as predicted in the generic class of two Higgs doublet models (2HDMs). No signal above the standard model background expectation is observed. Stringent upper limits on the cross section times branching fraction are set for Higgs bosons with masses up to 130 GeV. Lastly, the results are interpreted within several MSSM and 2HDM scenarios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Constraints on models of scalar and vector leptoquarks decaying to a quark and a neutrino at s = 13 TeV

Here, the results of a previous search by the CMS Collaboration for squarks and gluinos are reinterpreted to constrain models of leptoquark (LQ) production. The search considers jets in association with a transverse momentum imbalance, using the $M_\mathrm{T2}$ variable. The analysis uses proton-proton collision data at $\sqrt{s}=$ 13 TeV, recorded with the CMS detector at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Leptoquark pair production is considered with LQ decays to a neutrino and a top, bottom, or light quark. This reinterpretation considers higher mass values than the original CMS search to constrain both scalar and vector LQs. Limits on the cross section for LQ pair production are derived at the 95% confidence level depending on the LQ decay mode. A vector LQ decaying with a 50% branching fraction to t$\nu$, and 50% to b$\tau$, has been proposed as part of an explanation of anomalous flavor physics results. In such a model, using only the decays to t$\nu$, LQ masses below 1530 GeV are excluded assuming the Yang--Mills case with coupling $\kappa =$ 1, placing the most stringent constraint to date from pair production of vector LQs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for disappearing tracks as a signature of new long-lived particles in proton-proton collisions at $ \sqrt{s}=13 $ TeV

Here, a search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. A disappearing track is an isolated track with missing hits in the outer layers of the silicon tracker, little or no energy in associated calorimeter deposits, and no associated hits in the muon detectors. This search uses data collected with the CMS detector in 2015 and 2016 from proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC, corresponding to an integrated luminosity of 38.4 fb$^{-1}$. The results of the search are interpreted in the context of the anomaly-mediated supersymmetry breaking model. The data are consistent with the background-only hypothesis. Limits are set on the product of the cross section for direct production of charginos and their branching fraction to a neutralino and a pion, as a function of the chargino mass and lifetime. At 95% confidence level, charginos with masses below 715 (695) GeV are excluded for a lifetime of 3 (7) ns, as are charginos with lifetimes from 0.5 to 60 ns for a mass of 505 GeV. These are the most stringent limits using a disappearing track signature on this signal model for chargino lifetimes above $\approx$0.7 ns.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Constraining Gluon Distributions in Nuclei Using Dijets in Proton-Proton and Proton-Lead Collisions at s NN = 5.02 TeV

The pseudorapidity distributions of dijets as a function of their average transverse momentum ($p_\mathrm{T}^\text{ave}$) are measured in proton-lead (pPb) and proton-proton (pp) collisions. The data samples were collected by the CMS experiment at the CERN LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. A significant modification of the pPb spectra with respect to the pp spectra is observed in all $p_\mathrm{T}^\text{ave}$ intervals investigated. The ratios of the pPb and pp distributions are compared to next-to-leading order perturbative quantum chromodynamics calculations with unbound nucleon and nuclear parton distribution functions (PDFs). Furthermore, these results give the first evidence that the gluon PDF at large Bjorken $x$ in lead ions is strongly suppressed with respect to the PDF in unbound nucleons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for a singly produced third-generation scalar leptoquark decaying to a τ lepton and a bottom quark in proton-proton collisions at $ \sqrt{s}=13 $ TeV

Here, a search is presented for a singly produced third-generation scalar leptoquark decaying to a τ lepton and a bottom quark. Associated production of a leptoquark and a τ lepton is considered, leading to a final state with a bottom quark and two τ leptons. The search uses proton-proton collision data at a center-of-mass energy of 13 TeV recorded with the CMS detector, corresponding to an integrated luminosity of 35.9 fb$^{–1}$. Upper limits are set at 95% confidence level on the production cross section of the third-generation scalar leptoquarks as a function of their mass. From a comparison of the results with the theoretical predictions, a third-generation scalar leptoquark decaying to a τ lepton and a bottom quark, assuming unit Yukawa coupling (λ), is excluded for masses below 740 GeV. Limits are also set on λ of the hypothesized leptoquark as a function of its mass. Above λ = 1.4, this result provides the best upper limit on the mass of a third-generation scalar leptoquark decaying to a τ lepton and a bottom quark.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Observation of t t ¯ H Production

Here, the observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of √s=7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb -1 , respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is1.26 +0.31 –0.26 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Nuclear modification factor of D 0 mesons in PbPb collisions at s NN = 5.02 TeV

The transverse momentum ( p T ) spectrum of prompt D 0 mesons and their antiparticles has been measured via the hadronic decay channels D 0 → K – π + and D - 0 → K + π – in p p and PbPb collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair with the CMS detector at the LHC. The measurement is performed in the D 0 meson p T range of 2–100 GeV/ c and in the rapidity range of | y | < 1 . The p p (PbPb) dataset used for this analysis corresponds to an integrated luminosity of 27.4 pb –1 (530 μb –1 ). The measured D 0 meson p T spectrum in pp collisions is well described by perturbative QCD calculations. The nuclear modification factor, comparing D 0 meson yields in PbPb and p p collisions, was extracted for both minimum-bias and the 10% most central PbPb interactions. For central events, the D 0 meson yield in the PbPb collisions is suppressed by a factor of 5–6 compared to the p p reference in the p T range of 6–10 GeV/ c . For D 0 mesons in the high- p T range of 60–100 GeV/ c , a significantly smaller suppression is observed. The results are also compared to theoretical calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗