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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Search for new phenomena in events with a photon and missing transverse momentum in pp collisions at $$ \sqrt{s}=13 $$ TeV with the ATLAS detector

Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum with the ATLAS experiment at the Large Hadron Collider are reported. The data were collected in proton-proton collisions at a centre-of-mass energy of 13 TeV and correspond to an integrated luminosity of 3.2 fb -1 . The observed data are in agreement with the Standard Model expectations. Exclusion limits are presented in models of new phenomena including pair production of dark matter candidates or large extra spatial dimensions. In a simplified model of dark matter and an axial-vector mediator, the search excludes mediator masses below 710 GeV for dark matter candidate masses below 150 GeV. In an effective theory of dark matter production, values of the suppression scale M * up to 570 GeV are excluded and the effect of truncation for various coupling values is reported. Finally, for the ADD large extra spatial dimension model the search places more stringent limits than earlier searches in the same event topology, excluding M D up to about 2.3 (2.8) TeV for two (six) additional spatial dimensions; the limits are reduced by 20-40% depending on the number of additional spatial dimensions when applying a truncation procedure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

A search for top squarks with R-parity-violating decays to all-hadronic final states with the ATLAS detector in $ \sqrt{s}=8 $ TeV proton-proton collisions

A search for the pair production of top squarks, each with R -parity-violating decays into two Standard Model quarks, is performed using 17.4 fb -1 of √s=8 TeV proton-proton collision data recorded by the ATLAS experiment at the LHC. Each top squark is assumed to decay to a b- and an s-quark, leading to four quarks in the final state. Background discrimination is achieved with the use of b-tagging and selections on the mass and substructure of large-radius jets, providing sensitivity to top squark masses as low as 100 GeV. Finally, no evidence of an excess beyond the Standard Model background prediction is observed and top squarks decaying to $\overline{b}$$\overline{s}$ are excluded for top squark masses in the range 100 ≤ m $\overline{t}$ ≤ 315 GeV at 95% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurement of the relative width difference of the B 0 - B$\bar{B}$ 0 system with the ATLAS detector

This paper presents the measurement of the relative width difference ΔΓ d /Γ d of the B 0 - B$\bar{B}$ 0 system using the data collected by the ATLAS experiment at the LHC in pp collisions at √s=7TeV and √s=8 TeV and corresponding to an integrated luminosity of 25.2 fb -1 . The value of ΔΓ d /Γ d is obtained by comparing the decay-time distributions of B° → J/ψK S and B° → J/ψK*°(892) decays. The result is ΔΓ d /Γ d = (-0.1±1.1 (stat.)± 0.9 (syst.)) × 10 - 2. Currently, this is the most precise single measurement of ΔΓd/Γd. It agrees with the Standard Model prediction and the measurements by other experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Identification of high transverse momentum top quarks in pp collisions at $ \sqrt{s}=8 $ TeV with the ATLAS detector

This study presents studies of the performance of several jet-substructure techniques, which are used to identify hadronically decaying top quarks with high transverse momentum contained in large-radius jets. The efficiency of identifying top quarks is measured using a sample of top-quark pairs and the rate of wrongly identifying jets from other quarks or gluons as top quarks is measured using multijet events collected with the ATLAS experiment in 20.3 fb -1 of 8 TeV proton-proton collisions at the Large Hadron Collider. Predictions from Monte Carlo simulations are found to provide an accurate description of the performance. The techniques are compared in terms of signal efficiency and background rejection using simulations, covering a larger range in jet transverse momenta than accessible in the dataset. Finally and additionally, a novel technique is developed that is optimized to reconstruct top quarks in events with many jets.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Search for new phenomena in events with three or more charged leptons in pp collisions at $ \sqrt{s}=8 $ TeV with the ATLAS detector

A generic search for anomalous production of events with at least three charged leptons is presented. The data sample consists of pp collisions at √s=8 TeV collected in 2012 by the ATLAS experiment at the CERN Large Hadron Collider, and corresponds to an integrated luminosity of 20.3 fb -1 . Events are required to have at least three selected lepton candidates, at least two of which must be electrons or muons, while the third may be a hadronically decaying tau. Selected events are categorized based on their lepton flavour content and signal regions are constructed using several kinematic variables of interest. No significant deviations from Standard Model predictions are observed. Model-independent upper limits on contributions from beyond the Standard Model phenomena are provided for each signal region, along with prescription to re-interpret the limits for any model. Constraints are also placed on models predicting doubly charged Higgs bosons and excited leptons. For doubly charged Higgs bosons decaying to eτ or μτ, lower limits on the mass are set at 400 GeV at 95% confidence level. For excited leptons, constraints are provided as functions of both the mass of the excited state and the compositeness scale Λ, with the strongest mass constraints arising in regions where the mass equals Λ. In such scenarios, lower mass limits are set at 3.0 TeV for excited electrons and muons, 2.5 TeV for excited taus, and 1.6 TeV for every excited-neutrino flavour.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

A search for \( t\overline{t} \) resonances using lepton-plus-jets events in proton-proton collisions at \( \sqrt{s}=8 \) TeV with the ATLAS detector

A search for new particles that decay into top quark pairs is reported. The search is performed with the ATLAS experiment at the LHC using an integrated luminosity of 20.3 fb -1 of proton-proton collision data collected at a centre-of-mass energy of \( \sqrt{s}=8 \) TeV. The lepton-plus-jets final state is used, where the top pair decays to \( {W}^{+}b{W}^{-}\overline{b} \), with one W boson decaying leptonically and the other hadronically. The invariant mass spectrum of top quark pairs is examined for local excesses or deficits that are inconsistent with the Standard Model predictions. No evidence for a top quark pair resonance is found, and 95% confidence-level limits on the production rate are determined for massive states in benchmark models. The upper limits on the cross-section times branching ratio of a narrow Z' boson decaying to top pairs range from 4.2 pb to 0.03 pb for resonance masses from 0.4 TeV to 3.0 TeV. A narrow leptophobic topcolour Z' boson with mass below 1.8 TeV is excluded. Upper limits are set on the cross-section times branching ratio for a broad colour-octet resonance with Γ/m = 15% decaying to \( t\overline{t} \). These range from 4.8 pb to 0.03 pb for masses from 0.4 TeV to 3.0 TeV. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.2 TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for new particles in events with one lepton and missing transverse momentum in pp collisions at $ \sqrt{s} $ = 8 TeV with the ATLAS detector

This paper presents a search for new particles in events with one lepton (electron or muon) and missing transverse momentum using 20.3 fb -1 of proton-proton collision data at $ \sqrt{s} $ = 8 TeV recorded by the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. A W' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 3.24 TeV. Excited chiral bosons (W*) with equivalent coupling strengths are excluded for masses up to 3.21 TeV. In the framework of an effective field theory limits are also set on the dark matter-nucleon scattering cross-section as well as the mass scale M* of the unknown mediating interaction for dark matter pair production in association with a leptonically decaying W.[Figure not available: see fulltext.]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Erratum to: Measurement of the inclusive jet cross-section in proton-proton collisions at $ \sqrt{s}=7 $ TeV using 4.5 fb -1 of data with the ATLAS detector

It was found that the non-perturbative corrections calculated using Pythia with the Perugia 2011 tune did not include the effect of the underlying event. The affected correction factors were recomputed using the Pythia 6.427 generator. These corrections are applied as baseline to the NLO pQCD calculations and thus the central values of the theoretical predictions have changed by a few percent with the new corrections. This has a minor impact on the agreement between the data and the theoretical predictions. Figures 2 and 6 to 13, and all the tables have been updated with the new values. A few sentences in the discussion in sections 5.2 and 9 were altered or removed.[Figure not available: see fulltext.]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of the inclusive jet cross-sections in proton-proton collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

Inclusive jet production cross-sections are measured in proton-proton collisions at a centre-of-mass energy of √s=8 TeV recorded by the ATLAS experiment at the Large Hadron Collider at CERN. The total integrated luminosity of the analysed data set amounts to 20.2 fb -1 . Double-differential cross-sections are measured for jets defined by the anti-k t jet clustering algorithm with radius parameters of R = 0.4 and R = 0.6 and are presented as a function of the jet transverse momentum, in the range between 70 GeV and 2.5 TeV and in six bins of the absolute jet rapidity, between 0 and 3.0. The measured cross-sections are compared to predictions of quantum chromodynamics, calculated at next-to-leading order in perturbation theory, and corrected for non-perturbative and electroweak effects. The level of agreement with predictions, using a selection of different parton distribution functions for the proton, is quantified. Tensions between the data and the theory predictions are observed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for the direct production of charginos, neutralinos and staus in final states with at least two hadronically decaying taus and missing transverse momentum in pp collisions at $ \sqrt{s}=8 $ TeV with the ATLAS detector

We present results of a search for the electroweak associated production of charginos and next-to-lightest neutralinos, pairs of charginos or pairs of tau sleptons. These processes are characterised by final states with at least two hadronically decaying tau leptons, missing transverse momentum and low jet activity. The analysis is based on an integrated luminosity of 20.3 fb ₋1 of proton-proton collisions at √s = 8TeV recorded with the ATLAS experiment at the Large Hadron Collider. We observed no significant excess with respect to the predictions from Standard Model processes. Limits are set at 95% confidence level on the masses of the lighter chargino and next-to-lightest neutralino for various hypotheses for the lightest neutralino mass in simplified models. In the scenario of direct production of chargino pairs, with each chargino decaying into the lightest neutralino via an intermediate tau slepton, chargino masses up to 345 GeV are excluded for a massless lightest neutralino. For associated production of mass-degenerate charginos and next-tolightest neutralinos, both decaying into the lightest neutralino via an intermediate tau slepton, masses up to 410 GeV are excluded for a massless lightest neutralino.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Angular analysis of B$0\atop{d}$ → K*μ + μ - decays in pp collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

An angular analysis of the decay B$0\atop{d}$ → K*μ + μ - is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb -1 of integrated luminosity collected during 2012 at centre-of-mass energy of $\sqrt{s}=8 $ TeV. Measurements of the K* longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗