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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Search for invisible decays of the Higgs boson produced in association with a hadronically decaying vector boson in pp collisions at √s = 8 with the ATLAS detector

A search for Higgs boson decays to invisible particles is performed using 20.3 fb⁻¹ of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson (V = W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain V H production followed by H decaying to invisible particles for the Higgs boson mass range 115 < m H < 300 GeV. The 95 % confidence-level observed upper limit on σ VH × BR(H → inv.) varies from 1.6 pb at 115 GeV to 0.13 pb at 300 GeV. Assuming Standard Model production and including the gg → H contribution as signal, the results also lead to an observed upper limit of 78% at 95% confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

A search for decays of the Higgs boson to invisible particles in events with a top-antitop quark pair or a vector boson in proton-proton collisions at $$\sqrt{s} = 13\,\text {Te}\hspace{-.08em}\text {V} $$

A search for decays to invisible particles of Higgs bosons produced in association with a top-antitop quark pair or a vector boson, which both decay to a fully hadronic final state, has been performed using proton-proton collision data collected at $\sqrt{s} = 13$ TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138fb -1 . The 95% confidence level upper limit set on the branching fraction of the 125 GeV Higgs boson to invisible particles, B(H → inv), is 0.54 (0.39 expected), assuming standard model production cross sections. The results of this analysis are combined with previous B(H → inv) searches carried out at $\sqrt{s} = 7$, 8, and 13 TeV in complementary production modes. The combined upper limit at 95% confidence level on B(H → inv) is 0.15 (0.08 expected).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

An atomic orbital-based formulation of analytical gradients and nonadiabatic coupling vector elements for the state-averaged complete active space self-consistent field method on graphical processing units

We recently presented an algorithm for state-averaged complete active space self-consistent field (SA-CASSCF) orbital optimization that capitalizes on sparsity in the atomic orbital basis set to reduce the scaling of computational effort with respect to molecular size. Here, we extend those algorithms to calculate the analytic gradient and nonadiabatic coupling vectors for SA-CASSCF. Combining the low computational scaling with acceleration from graphical processing units allows us to perform SA-CASSCF geometry optimizations for molecules with more than 1000 atoms. The new approach will make minimal energy conical intersection searches and nonadiabatic dynamics routine for molecular systems with O(10{sup 2}) atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Measurement of the electroweak production of dijets in association with a Z-boson and distributions sensitive to vector boson fusion in proton-proton collisions at $ \sqrt{s} $ = 8 TeV using the ATLAS detector

Measurements of fiducial cross sections for the electroweak production of two jets in association with a Z-boson are presented. The measurements are performed using 20.3 fb -1 of proton-proton collision data collected at a centre-of-mass energy of √s = 8 TeV by the ATLAS experiment at the Large Hadron Collider. The electroweak component is extracted by a fit to the dijet invariant mass distribution in a fiducial region chosen to enhance the electroweak contribution over the dominant background in which the jets are produced via the strong interaction. The electroweak cross sections measured in two fiducial regions are in good agreement with the Standard Model expectations and the background-only hypothesis is rejected with significance above the 5σ level. The electroweak process includes the vector boson fusion production of a Z-boson and the data are used to place limits on anomalous triple gauge boson couplings. In addition, measurements of cross sections and differential distributions for inclusive Z-boson-plus-dijet production are performed in five fiducial regions, each with different sensitivity to the electroweak contribution. The results are corrected for detector effects and compared to predictions from the Sherpa and Powheg event generators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Search for single production of vector-like quarks decaying into Wb in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for singly produced vector-like quarks Q , where Q can be either a T quark with charge +2/3 or a Y quark with charge ₋4/3, is performed in proton–proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb ₋1 , recorded with the ATLAS detector at the LHC in 2015 and 2016. The analysis targets Q → Wb decays where the W boson decays leptonically. No crtical deviation from the expected Standard Model background is observed. Upper limits are set on the QWb coupling strength and the mixing between the Standard Model sector and a singlet T quark or a Y quark from a ( B, Y ) doublet or a ( T, B, Y ) triplet, taking into account the interference effects with the Standard Model background. The upper limits set on the mixing angle are as small as |sin θ L | = 0.18 for a singlet T quark of mass 800 GeV, |sin θ R | = 0.17 for a Y quark of mass 800 GeV in a ( B, Y ) doublet model and |sin θL| = 0.16 for a Y quark of mass 800 GeV in a ( T, B, Y ) triplet model. Within a ( B, Y ) doublet model, the limits set on the mixing parameter |sin θ R | are comparable with the exclusion limits from electroweak precision observables in the mass range between about 900 GeV and 1250 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Predicting Reaction Products and Automating Reactive Trajectory Characterization in Molecular Simulations with Support Vector Machines

A machine learning-based methodology for the prediction of chemical reaction products, along with automated elucidation of mechanistic details via phase space analysis of reactive trajectories, is introduced using low-dimensional heuristic models and then applied to ab initio computer simulations of the photodissociation of acetaldehyde, an important chemical system in atmospheric chemistry. Our method is centered around training Support Vector Machines (SVMs) to identify optimal separatrices that delineate the regions of phase space that lead to different chemical reaction products. In contrast to the more common “black box” type machine learning methodologies for analyzing chemical simulation data, this SVM-based methodology allows for mechanistic insight to be gleaned from further analysis of the positioning of the phase space points used to train the SVM with respect to the separatrices. For example, a pair of phase space points that are in close proximity to each other but on opposite sides of a separatrix may be situated on opposite sides of a transition state, while phase space points occurring early in a simulation that are distant from a separatrix are likely to belong to trajectories that are highly biased toward the product state associated with the basin of attraction to which they belong. In addition to inferring mechanistic details about multiple-pathway chemical reactions, our method can also be used to increase reactive trajectory sampling efficiency in molecular simulations via rejection sampling, with trajectories leading to undesired product states being identified and terminated early in the simulation rather than being carried to completion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Vector-boson-tagged jet production in heavy ion collisions at energies available at the CERN Large Hadron Collider [Vector boson-tagged jet production in heavy ion collisions at the LHC]

Here, vector-boson-tagged jet production in collisions of heavy nuclei opens new opportunities to study parton shower formation and propagation in strongly interacting matter. It has been argued to provide a golden channel that can constrain the energy loss of jets in the quark-gluon plasma created in heavy ion reactions. We present theoretical results for isolated-photon-tagged and Z 0 -boson-tagged jet production in Pb + Pb collisions with √s NN = 5.02TeV at the LHC. Specifically, we evaluate the transverse momentum imbalance x JV distribution and nuclear modification factor I AA of tagged jets and compare our theoretical calculations to recent experimental measurements by ATLAS and CMS collaborations. Our analysis, which includes both collisional and radiative energy losses, sheds light on their relative importance versus the strength of jet-medium interactions and helps quantify the amount of out-of-cone radiation of predominantly prompt quark-initiated jets.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Search for a heavy vector boson decaying to two gluons in pp̄ collisions at √s=1.96 TeV

We present a search for a new heavy vector boson Z' that decays to gluons. Decays to on-shell gluons are suppressed, leading to a dominant decay mode of Z'→g*g. We study the case where the off-shell gluon g* converts to a pair of top quarks, leading to a final state of tt¯g. In a sample of events with exactly one charged lepton, large missing transverse momentum and at least five jets, corresponding to an integrated luminosity of 8.7 fb⁻¹ collected by the CDF II detector, we find the data to be consistent with the standard model. We set upper limits on the production cross section times branching ratio of this chromophilic Z' at 95% confidence level from 300 to 40 fb for Z' masses ranging from 400 to 1000 GeV/c², respectively.

Aaltonen, T.↗
DOE OSTI2016

Search for the standard model Higgs boson produced in association with a vector boson and decaying into a tau pair in p p collisions at s = 8 TeV with the ATLAS detector

A search for the standard model Higgs boson produced in association with a vector boson with the decay H → τ τ is presented. The data correspond to 20.3 fb -1 of integrated luminosity from proton-proton collisions at √ s = 8 TeV recorded by the ATLAS experiment at the LHC during 2012.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Motional displacements in proteins: The origin of wave-vector-dependent values

In the case of average mean-square displacement, r 2 , of H atoms in a protein, it is frequently determined using incoherent neutron-scattering experiments. r 2 is obtained from the observed elastic incoherent dynamic structure factor, S i (Q,ω =0), assuming the form S i (Q, ω =0) =exp( -Q 2 r 2 /3). Moreover, this is often referred to as the Gaussian approximation (GA) to S i (Q, ω =0). r 2 obtained in this way depends on the value of the wave vector, Q considered. Equivalently, the observed S i (Q, ω =0) deviates from the GA. We investigate the origin of the Q dependence of r 2 by evaluating the scattering functions in different approximations using molecular dynamics (MD) simulation of the protein lysozyme. We find that keeping only the Gaussian term in a cumulant expansion of S(Q, ω ) is an accurate approximation and is not the origin of the Q dependence of r 2 . We demonstrated by showing that the term beyond the Gaussian is negligible and that the GA is valid for an individual atom in the protein. Rather, the Q dependence (deviation from the GA) arises from the dynamical heterogeneity of the H in the protein. Specifically it arises from representing, in the analysis of data, this diverse dynamics by a single average scattering center that has a single, average r 2 . The observed Q dependence of r 2 can be used to provide information on the dynamical heterogeneity in proteins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Search for single production of vector-like quarks decaying into Wb in pp collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector

A search for singly produced vector-like Q quarks, where Q can be either a T quark with charge +2/3 or a Y quark with charge –4/3, is performed in proton–proton collisions recorded with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 20.3 fb –1 and was produced with a centre-of-mass energy of √s = 8 TeV. This analysis targets Q → Wb decays where the W boson decays leptonically. A veto on massive large-radius jets is used to reject the dominant tt¯ background. The reconstructed Q-candidate mass, ranging from 0.4 to 1.2 TeV, is used in the search to discriminate signal from background processes. No significant deviation from the Standard Model expectation is observed, and limits are set on the Q → Wb cross-section times branching ratio. The results are also interpreted as limits on the QWb coupling and the mixing with the Standard Model sector for a singlet T quark or a Y quark from a doublet. T quarks with masses below 0.95 TeV are excluded at 95 % confidence level, assuming a unit coupling and a BR(T → Wb) = 0.5, whereas the expected limit is 1.10 TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗