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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Analysis of the Wtb vertex from the measurement of triple-differential angular decay rates of single top quarks produced in the t -channel at $ \sqrt{s}=8 $ TeV with the ATLAS detector

The electroweak production and subsequent decay of single top quarks in the t-channel is determined by the properties of the Wtb vertex, which can be described by the complex parameters of an effective Lagrangian. We use an analysis of a triple-differential decay rate in t-channel production to simultaneously determine five generalised helicity fractions and phases, as well as the polarisation of the produced top quark. The complex parameters are then constrained. This analysis is based on 20.2 fb -1 of proton-proton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the LHC. The fraction of decays containing transversely polarised W bosons is measured to be f 1 = 0.30 ± 0.05. The phase between amplitudes for transversely and longitudinally polarised W bosons recoiling against left-handed b-quarks is measured to be δ - = 0.002π + 0.017π + 0.016π , giving no indication of CP violation. The fractions of longitudinal or transverse W bosons accompanied by right-handed b-quarks are also constrained. Based on these measurements, limits are placed at 95% CL on the ratio of the complex coupling parameters Re [g R /V L ϵ [-0.12, 0.17] and Im [g R /V L ϵ [-0.07, 0.06]. Constraints are also placed on the ratios |V R /V L | and |g L /V L |. Additionally, the polarisation of single top quarks in the t-channel is constrained to be P > 0.72 (95% CL). None of the above measurements make assumptions about the value of any of the other parameters or couplings and all of them are in agreement with the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Probing effective field theory operators in the associated production of top quarks with a Z boson in multilepton final states at $\sqrt{s}$ = 13 TeV

A search for new top quark interactions is performed within the framework of an effective field theory using the associated production of either one or two top quarks with a Z boson in multilepton final states. The data sample corresponds to an integrated luminosity of 138 fb -1 of proton-proton collisions at √s = 13 TeV collected by the CMS experiment at the LHC. Five dimension-six operators modifying the electroweak interactions of the top quark are considered. Novel machine-learning techniques are used to enhance the sensitivity to effects arising from these operators. Distributions used for the signal extraction are parameterized in terms of Wilson coefficients describing the interaction strengths of the operators. All five Wilson coefficients are simultaneously fit to data and 95% confidence level intervals are computed. All results are consistent with the SM expectations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4ℓ events with the ATLAS detector at $ \sqrt{s} $ = 13 TeV

A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb –1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 ± 0.60 fb, consistent with the next-to-leading-order Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for flavour-changing neutral $tqH$ interactions with $H$ → γγ in $pp$ collisions at $ \sqrt{s} $ = 13 TeV using the ATLAS detector

A search for flavour-changing neutral interactions involving the top quark, the Higgs boson and an up-type quark q (q = c, u) is presented. The proton-proton collision data set used, with an integrated luminosity of 139 fb –1 , was collected at $\sqrt{s}$ = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Both the decay process t → qH in $t\bar{t}$ production and the production process pp → tH, with the Higgs boson decaying into two photons, are investigated. No significant excess is observed and upper limits are set on the t → cH and the t → uH branching ratios of 4.3 × 10 –4 and 3.8 × 10 –4 , respectively, at the 95% confidence level, while the expected limits in the absence of signal are 4.7 × 10 –4 and 3.9 × 10 –4 . Combining this search with ATLAS searches in the H → τ + τ – and H → $b\bar{b}$ final states yields observed (expected) upper limits on the t → cH branching ratio of 5.8 × 10 –4 (3.0 × 10 –4 ) at the 95% confidence level. The corresponding observed (expected) upper limit on the t → uH branching ratio is 4.0 × 10 –4 (2.4 × 10 –4 ).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Measurement of the effective leptonic weak mixing angle

Using pp collision data at $\sqrt{s}$ = 13 TeV, recorded by the LHCb experiment between 2016 and 2018 and corresponding to an integrated luminosity of 5.4 fb −1 , the forward-backward asymmetry in the pp → Z/γ* → μ + μ − process is measured. The measurement is carried out in ten intervals of the difference between the muon pseudorapidities, within a fiducial region covering dimuon masses between 66 and 116 GeV, muon pseudorapidities between 2.0 and 4.5 and muon transverse momenta above 20 GeV. These forward-backward asymmetries are compared with predictions, at next-to-leading order in the strong and electroweak couplings. The measured effective leptonic weak mixing angle is ${\sin}^2{\theta}_{\textrm{eff}}^{\ell }=0.23147\pm 0.00044\pm 0.00005\pm 0.00023,$ where the first uncertainty is statistical, the second arises from systematic uncertainties associated with the asymmetry measurement, and the third arises from uncertainties in the fit model used to extract ${\sin}^2{\theta}_{\textrm{eff}}^{\ell }$ from the asymmetry measurement. This result is based on an arithmetic average of results using the CT18, MSHT20, and NNPDF31 parameterisations of the proton internal structure, and is consistent with previous measurements and with predictions from the global electroweak fit.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

The effective chiral Lagrangian from the theta term

We construct the effective chiral Lagrangian involving hadronic and electromagnetic interactions originating from the QCD {theta}-bar term. We impose vacuum alignment at both quark and hadronic levels, including field redefinitions to eliminate pion tadpoles. We show that leading time-reversal-violating (TV) hadronic interactions are related to isospin-violating interactions that can in principle be determined from charge-symmetry-breaking experiments. We discuss the complications that arise from TV electromagnetic interactions. Some implications of the expected sizes of various pion-nucleon TV interactions are presented, and the pion-nucleon form factor is used as an example.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Non-perturbative methods for a chiral effective field theory of finite density nuclear systems

Recently we have developed a novel chiral power counting scheme for an effective field theory of nuclear matter with nucleons and pions as degrees of freedom . It allows for a systematic expansion taking into account both local as well as pion-mediated multi-nucleon interactions. We apply this power counting in the present study to the evaluation of the pion self-energy and the energy density in nuclear and neutron matter at next-to-leading order. To implement this power counting in actual calculations we develop here a non-perturbative method based on Unitary Chiral Perturbation Theory for performing the required resummations. We show explicitly that the contributions to the pion self-energy with in-medium nucleon-nucleon interactions to this order cancel. The main trends for the energy density of symmetric nuclear and neutron matter are already reproduced at next-to-leading order. In addition, an accurate description of the neutron matter equation of state, as compared with sophisticated many-body calculations, is obtained by varying only slightly a subtraction constant around its expected value. The case of symmetric nuclear matter requires the introduction of an additional fine-tuned subtraction constant, parameterizing the effects from higher order contributions. With that, the empirical saturation point and the nuclear matter compressibility are well reproduced while the energy per nucleon as a function of density closely agrees with sophisticated calculations in the literature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Similarity renormalization group evolution of chiral effective nucleon-nucleon potentials in the subtracted kernel method approach

Research Highlights: > We study the similarity renormalization group evolution of chiral NN potentials. > We evolve an effective potential derived using a subtractive renormalization scheme. > Unitarity of the SRG evolution is verified within the subtractive scheme. > High- and low-momentum components decouple for the SRG evolved potential. - Abstract: Methods based on Wilson's renormalization group have been successfully applied in the context of nuclear physics to analyze the scale dependence of effective nucleon-nucleon (NN) potentials, as well as to consistently integrate out the high-momentum components of phenomenological high-precision NN potentials in order to derive phase-shift equivalent softer forms, the so called V{sub low-k} potentials. An alternative renormalization group approach that has been applied in this context is the similarity renormalization group (SRG), which is based on a series of continuous unitary transformations that evolve hamiltonians with a cutoff on energy differences. In this work we study the SRG evolution of a leading order (LO) chiral effective NN potential in the {sup 1}S{sub 0} channel derived within the framework of the subtracted kernel method (SKM), a renormalization scheme based on a subtracted scattering equation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Nuclear binding energy and symmetry energy of nuclear matter with modern nucleon-nucleon potentials

Research Highlights: > The nuclear matter is studied within the Brueckner-Hartree-Fock (BHF) approach employing the most recent accurate nucleon-nucleon potentials. > The results come out by approximating the single particle self-consistent potential with a parabolic form. > We discuss the current status of the Coester line, i.e., density and energy of the various saturation points being strongly linearly correlated. > The nuclear symmetry energy is calculated as the difference between the binding energy of pure neutron matter and that of symmetric nuclear matter. - Abstract: The binding energy of nuclear matter at zero temperature in the Brueckner-Hartree-Fock approximation with modern nucleon-nucleon potentials is studied. Both the standard and continuous choices of single particle energies are used. These modern nucleon-nucleon potentials fit the deuteron properties and are phase shifts equivalent. Comparison with other calculations is made. In addition we present results for the symmetry energy obtained with different potentials, which is of great importance in astrophysical calculation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

A study of the ground-state energy of {sup 4}He with nucleon-nucleon potentials

Ground-state properties are evaluated for the finite nucleus {sup 4}He starting from realistic nucleon-nucleon interactions within the framework of the Green's function approach. For the sake of comparison, the same calculations are performed using the Brueckner-Hartree-Fock approximation. For that purpose four high-quality modern nucleon-nucleon interactions represented in momentum space are employed: the Argonne V18, CD-Bonn, Bonn A and N{sup 3}LO potentials. In these potentials, the effects of charge dependence are taken into account. Additional binding energy is obtained from the inclusion of the hole-hole scattering term within the framework of the Green function approach. It has been shown that the Green function results agree well with the results obtained by accurate methods for few-nucleon systems such as the Faddeev-Yakubovsky calculation. In this study, a comparison of the calculated ground-state energies, obtained by using the Green function approach and different nucleon-nucleon potentials, with experimental values is carried out. The results show good agreement between the calculated values and the experimental ones. - Highlights: > We present ground-state energies of the helium nucleus. > We consider four high-quality modern nucleon-nucleon potentials. > It is shown that the Green function approach gives quite good results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Mexican contribution to ALICE and first data analysis

On November 2009 the Large Hadron Collider produced the first p+p collisions. These, together with the upcoming Pb+Pb data, open up the possibility to answer some of the intriguing questions regarding the Standard Model and likely bring to light new phenomena. In this work I present a short review of the mexican participation in the ALICE experiment, focusing on the detector building and phenemological as well as Monte Carlo simulation work regarding the proton as well as the heavy ion program. I also briefly mention some of the wide spectrum of possible first topics that can be analyzed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

B Physics at the D0 experiment A Mexican review

On April of 1992 a Mexican group from Cinvestav officially joined the D0 experiment, one of the two experiments in the Tevatron collider at Fermilab. The seed for this experimental group on high energy physics from Cinvestav was planted in Mexico in some measure by Augusto Garcia, to whom this workshop is in memorial. Augusto's efforts and support to groups dedicated to this area was clear and important. Some of these seeds have given origin to today's established Mexican groups on experimental high energy physics, one example of this is the Mexican group at D0. I present here a short review of some of the D0 results on which the Mexican group has contributed, emphasizing the last decade, which I have witnessed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Intermediate pT phenomena in relativistic heavy-ion collisions

Particles produced with intermediate values of transverse momentum 1-2(less-or-similar sign)pT(less-or-similar sign)4-5 GeV, exhibit both thermal and jet-like features making them an ideal testing ground of the properties of the quark-gluon plasma produced in the aftermath of a relativistic heavy-ion collision, which have been only inferred from the behavior of either soft or hard modes. In this work I discuss two phenomena that that are observed in this transverse momentum window: the suppression of the single, non-photonic electron yield compared to normalized p+p collisions and the spin alignment of vector mesons. I make use of a recombination scenario of either a heavy or a fast quark with thermal ones and show that this way of describing hadron formation can account for the afore mentioned phenomena.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Travels with Tony - -nucleon structure through our ages

Nucleon structure is currently understood from a unified light-front, infinite-momentum-frame framework. The specific examples of the neutron transverse charge distribution and the shape of the proton are discussed here.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Lattice investigation of nucleon structure at light quark masses

Lattice simulations of hadronic structure are now reaching a level where they are able to not only complement, but also provide guidance to current and forthcoming experimental programmes at, e.g. Jefferson Lab, COMPASS/CERN and FAIR/GSI. By considering new simulations at low quark masses and on large volumes, we review the recent progress that has been made in this exciting area by the QCDSF/UKQCD collaboration. In particular, results obtained close to the physical point for several quantities, including electromagnetic form factors and moments of ordinary parton distribution functions, show some indication of approaching their phenomenological values.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Unravelling strange quarks in nucleon structure

We present a discourse on the stages of discovery that have led to a deeper understanding of the role played by strange quarks in the structure of the nucleon.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Crossing symmetric potential model of pion-nucleon scattering

A crossing symmetric {pi}N scattering amplitude is constructed through a complete attachment of two external pions to the dressed nucleon propagator of an underlying {pi}N potential model. Our formulation automatically provides expressions also for the crossing symmetric and gauge invariant pion photoproduction and Compton scattering amplitudes. We show that our amplitudes are unitary if they coincide on-shell with the amplitudes obtained by attaching one pion to the dressed {pi}NN vertex of the same potential model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗