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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 847 records · Page 47
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DOE OSTI2014

Search for strong production of supersymmetric particles in final states with missing transverse momentum and at least three b -jets at s = 8 TeV proton-proton collisions with the ATLAS detector

CERN-LHC. This paper reports the results of a search for strong production of supersymmetric particles in 20.1 fb-1 of proton-proton collisions at a centre-of-mass energy of 8 TeV using the ATLAS detector at the LHC. The search is performed separately in events with either zero or at least one high-pT lepton (electron or muon), large missing transverse momentum, high jet multiplicity and at least three jets identified as originated from the fragmentation of a b-quark. No excess is observed with respect to the Standard Model predictions. The results are interpreted in the context of several supersymmetric models involving gluinos and scalar top and bottom quarks, as well as a mSUGRA/CMSSM model. Gluino masses up to 1340 GeV are excluded, depending on the model, significantly extending the previous ATLAS limits.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for non-pointing and delayed photons in the diphoton and missing transverse momentum final state in 8 TeV p p collisions at the LHC using the ATLAS detector

CERN-LHC. A search has been performed, using the full data sample of 20.3 fb-1 of 8 TeV proton-proton collisions collected in 2012 with the ATLAS detector at the LHC, for photons originating from a displaced vertex due to the decay of a neutral long-lived particle into a photon and an invisible particle. The analysis investigates the diphoton plus missing transverse momentum final state, and is therefore most sensitive to pair-production of long-lived particles. The analysis technique exploits the capabilities of the ATLAS electromagnetic calorimeter to make precise measurements of the flight direction, as well as the time of flight, of photons. No excess is observed over the Standard Model predictions for background. Exclusion limits are set within the context of Gauge Mediated Supersymmetry Breaking models, with the lightest neutralino being the next-to-lightest supersymmetric particle and decaying into a photon and gravitino with a lifetime in the range from 250 ps up to about 100 ns.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for dark matter in events with heavy quarks and missing transverse momentum in p p collisions with the ATLAS detector

CERN-LHC. This article reports on a search for dark matter pair production in association with bottom or top quarks in 20.3 fb 8 of pp collisions collected at sqrt(s) = 8 TeV by the ATLAS detector at the LHC. Events with large missing transverse momentum are selected when produced in association with high-momentum jets of which one or more are identified as jets containing b -quarks. Final states with top quarks are selected by requiring a high jet multiplicity and in some cases a single lepton. The data are found to be consistent with the Standard Model expectations and limits are set on the mass scale of effective field theories that describe scalar and tensor interactions between dark matter and Standard Model particles. Limits on the dark-matter=8 TeV by the ATLAS detector at the LHC. Events with large missing transverse momentum are selected when produced in association with high-momentum jets of which one or more are identified as jets containing b-quarks. Final states with top quarks are selected by requiring a high jet multiplicity and in some cases a single lepton. The data are found to be consistent with the Standard Model expectations and limits are set on the mass scale of effective field theories that describe scalar and tensor interactions between dark matter and Standard Model particles. Limits on the dark-matter--nucleon cross-section for spin-independent and spin-dependent interactions are also provided. These limits are particularly strong for low-mass dark matter. Using a simplified model, constraints are set on the mass of dark matter and of a coloured mediator suitable to explain a possible signal of annihilating dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Measurement of three-jet production cross-sections in p p collisions at 7 TeV centre-of-mass energy using the ATLAS detector

CERN-LHC. Double-differential three-jet cross-sections have been measured in proton-proton collisions at a centre-of-mass energy of sqrt(s)=7 TeV using the ATLAS detector at the Large Hadron Collider. The measurements are presented as functions of the three-jet invariant mass (m_jjj) and the sum of absolute rapidity separations between the three leading jets (|Y*|). Invariant masses extending up to 5 TeV are reached for 8<|Y*|<10. These measurements use the sample of proton-proton collision data recorded using the ATLAS detector in 2011, which corresponds to an integrated luminosity of 4.51 fb^-1. Jets are identified using the anti-kt algorithm with two different jet radius parameters, R=0.4 and R=0.6. The dominant uncertainty in this measurement comes from the jet energy scale. Next-to-leading-order QCD calculations corrected to account for non-perturbative effects are compared to the measurements. Good agreement is found between the data and the theoretical predictions based on most of the available sets of parton distribution functions, over the full kinematic range, covering almost seven orders of magnitude in the measured cross-section values.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for pair production of heavy vector-like quarks decaying to high- p m a t h r m T W bosons and b quarks in the lepton-plus-jets final state in p p collisions at s =13 TeV with the ATLAS detector

CERN-LHC, ATLAS. Limits on pair production of a heavy vector-like T quark together with its antiparticle, where the T quark decays to a W boson and a b quark. The search is based on 36.1 +\- 1.2 fb^{-1} of pp collisions at sqrt{s} = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton plus jets final state, including at least one b-tagged jet and a large-radius jet identified as originating from the hadronic decay of a high-momentum W boson. The search is also sensitive to a heavy vector-like B quark, in particular in the decay to Wt and the results are thus reinterpreted to provide limits on the B mass. Mass limits on both T and B production are also set as a function of the decay branching ratios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of inclusive jet and dijet cross-sections in proton-proton collisions at s = 13 TeV with the ATLAS detector

Measurement of inclusive jet cross-sections with the ATLAS Detector at a centre-of-mass energy 13 TeV Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb$^{−1} recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-kt algorithm with a radius parameter value of R=0.4. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to |y|=3. The double-differential dijet production cross-sections are presented as a function of the dijet mass, covering the range from 300 GeV to 9 TeV, and the half absolute rapidity separation between the two leading jets within |y|<3, y∗, up to y∗=3. Next-to-leading-order, and next-to-next-to-leading-order for the inclusive jet measurement, perturbative QCD calculations corrected for non-perturbative and electroweak effects are compared to the measured cross-sections.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for pair production of heavy vector-like quarks decaying into high- p T W bosons and top quarks in the lepton-plus-jets final state in p p collisions at s = 13 TeV with the ATLAS detector

CERN-LHC, ATLAS. Limits on pair production of a heavy vector-like B quark together with its antiparticle, where the B quark decays to a W boson and a top quark. The search is based on 36.1 +\- 0.8 fb^{-1} of pp collisions at sqrt{s} = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton plus jets final state, including at least four small jets out of which at least one is required to be b-tagged jet and a large-radius jet. Mass limits on B production are set as a function of the decay branching ratios.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for new phenomena in events with same-charge leptons and b -jets in p p collisions at s = 13 TeV with the ATLAS detector

CERN-LHC, ATLAS. This result is a search for new phenomena in events with two same-charge leptons or three leptons and jets identified as originating from b-quarks in a data sample of 36.1 fb−1 of pp collisions at √s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. No significant excess is found and limits are set on vector-like quark, four-top-quark, and same-sign top-quark pair production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for low-mass dijet resonances using trigger-level jets with the ATLAS detector in p p collisions at sqrt(s)=13 TeV

Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, whose data-collection rates at low transverse momentum are much lower than the rate from Standard Model multijet production. This data refers to a search for dijet resonances using a strategy called "Trigger-object Level Analysis" (TLA) in ATLAS, where the limitation on high-rate events that can be used for the search is overcome by recording only the event information calculated by the jet trigger algorithms, thereby allowing much higher event rates with reduced storage needs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Cross-section measurements of the Higgs boson decaying to a pair of tau leptons in proton--proton collisions at s = 13 TeV with the ATLAS detector

A measurement of total production cross sections of the Higgs boson in proton-proton collisions is presented in the H -> tau tau decay channel. The analysis is performed using 36.1 fb-1 of data recorded by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy of 13 TeV. All combinations of leptonic and hadronic tau decays are considered. The H->tau tau signal over the expected background from other Standard Model processes is established with an observed (expected) significance of 4.4 (4.1) standard deviations. Combined with results using data taken at 7 and 8 TeV centre-of-mass energies, the observed (expected) significance amounts to 6.4 (5.4) standard deviations and constitutes an observation of H->tautau decays by the ATLAS experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Search for heavy charged long-lived particles in the ATLAS detector in 31.6 fb &#x2212; 1 of proton-proton collision data at s = 13 TeV

CERN-LHC. Search for heavy charged long-lived particles in the ATLAS detector in 36.1/fb of proton-proton collision data at sqrt(s) = 13 TeV. A search for heavy charged long-lived particles is performed using a data sample of 36.1/fb of proton-proton collisions at sqrt(s) = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model-independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks (R-hadrons), charginos and staus. No significant deviations from the expected Standard Model background are observed. Upper limits at 95% confidence level are provided on the production cross sections of long-lived R-hadrons as well as directly pair-produced staus and charginos. These results translate into lower limits on the masses of long-lived gluino, sbottom and stop R-hadrons, as well as staus and charginos of 2000 GeV, 1250 GeV, 1340 GeV, 430 GeV and 1090 GeV, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Search for a right-handed gauge boson decaying into a high-momentum heavy neutrino and a charged lepton in p p collisions with the ATLAS detector at s = 13 TeV

CERN-LHC, ATLAS. A search for a right-handed gauge boson WR, decaying into a boosted right-handed heavy neutrino NR, in the framework of Left-Right Symmetric Models is presented. It is based on data from proton-proton collisions with a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015, 2016 and 2017, corresponding to an integrated luminosity of 80 fb−1. The search is performed separately for electrons and muons in the final state. A distinguishing feature of the search is the use of large-radius jets containing electrons. Selections based on the signal topology result in smaller background compared with to expected signal. No significant deviation from the Standard Model prediction is observed and lower limits are set in the WR and NR mass plane. Mass values of the WR smaller than 3.8-5 TeV are excluded for NR in the mass range 0.1-1.8 TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Upgrade and Operation of the ATLAS Radiation Interlock System (ARIS)

ATLAS (the Argonne Tandem Linac Accelerator Sys-tem) is a superconducting heavy ion accelerator which can accelerate nearly all stable, and some unstable, iso-topes between hydrogen and uranium. Prompt radiation fields from gamma and or neutron are typically below 1 rem/hr at 30 cm, but are permitted up to 300 rem/hr at 30 cm. The original ATLAS Radiation Interlock System (ARIS), hereafter referred to as ARIS 1.0 was installed 30 years ago. While it has been a functional critical safe-ty system, its age has exposed the facility to high risk of temporary shutdown due to failure of obsolete compo-nents. Topics discussed will be architecture, hardware improvements, functional improvements, and operation permitting personnel access to areas with low levels of radiation.

Blomberg, B. R.↗
DOE OSTI2019

Search for lepton-flavour-violating decays of the $Z$ boson into a $\tau$-lepton and a light lepton with the ATLAS detector

Lepton flavour violation in the charged lepton sector is an unambiguous signal of physics beyond the Standard Model. Searches for lepton flavour violation in decays of the Z Z boson with the ATLAS detector is reported, focusing on decays into an electron or muon and a hadronically decaying \tau τ -lepton, using pp p p collisions data with a centre-of-mass energy of 13 TeV. Upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95% confidence level: \mathcal{B}(Z\to e\tau) < 5.8\times10^{-5} ℬ ( Z → e τ ) < 5.8 × 10 − 5 and \mathcal{B}(Z\to \mu\tau) < 2.4\times10^{-5} ℬ ( Z → μ τ ) < 2.4 × 10 − 5 . When combined with a previous ATLAS result based on pp p p collisions data with a centre-of-mass energy of 8 TeV, an upper limit of \mathcal{B}(Z\to \mu\tau) < 1.3\times10^{-5} ℬ ( Z → μ τ ) < 1.3 × 10 − 5 is obtained.

Chan, Wing Sheung↗