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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 1,189 records · Page 66
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DOE OSTI2020

Study of the lineshape of the χ c1 (3872) state

A study of the lineshape of the χ c1 (3872) state is made using a data sample corresponding to an integrated luminosity of 3 fb –1 collected in pp collisions at center-of-mass energies of 7 and 8 TeV with the LHCb detector. Candidate χ c1 (3872) and ψ(2S) mesons from b-hadron decays are selected in the J/ψπ + π – decay mode. Describing the lineshape with a Breit-Wigner function, the mass splitting between the χ c1 (3872) and ψ(2S) states, Δm, and the width of the χ c1 (3872) state, Γ BW , are determined to be Δm=185.598 ± 0.067 ± 0.068 MeV, Γ BW = 1.39 ± 0.24 ± 0.10 MeV, where the first uncertainty is statistical and the second systematic. Using a Flatté-inspired model, the mode and full width at half maximum of the lineshape are determined to be mode = 3871.69+0.00+0.05 – 0.04–0.13 MeV, FWHM=0.22 +0.07+0.11–0.06–0.13 MeV. An investigation of the analytic structure of the Flatté amplitude reveals a pole structure, which is compatible with a quasibound D 0 D¯ *0 state but a quasivirtual state is still allowed at the level of 2 standard deviations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Classical and quantum evolution in a simple coherent neutrino problem

The extraordinary neutrino flux produced in extreme astrophysical environments like the early Universe, core-collapse supernovae and neutron star mergers may produce coherent quantum neutrino oscillations on macroscopic length scales. The Hamiltonian describing this evolution can be mapped into quantum spin models with all-to-all couplings arising from neutrino-neutrino forward scattering. To date many studies of these oscillations have been performed in a mean-field limit where the neutrinos time evolve in a product state. In this paper we examine a simple two-beam model evolving from an initial product state and compare the mean-field and many-body evolution. The symmetries in this model allow us to solve the real-time evolution for the quantum many-body system for hundreds or thousands of spins, far beyond what would be possible in a more general case with an exponential number (2 N ) of quantum states. We compare mean-field and many-body solutions for different initial product states and ratios of one- and two-body couplings, and find that in all cases in the limit of infinite spins the mean-field (product state) and many-body solutions coincide for simple observables. This agreement can be understood as a consequence of the fact that the typical initial condition represents a very local but dense distribution about a mean energy in the spectrum of the Hamiltonian. We explore quantum information measures like entanglement entropy and purity of the many-body solutions, finding intriguing relationships between the quantum information measures and the dynamical behavior of simple physical observables.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Nucleon isovector axial form factors

We present results for the isovector axial vector form factors obtained using thirteen 2 + 1 + 1 -flavor highly improved staggered quark (HISQ) ensembles generated by the MILC collaboration. The calculation of nucleon two- and three-point correlation functions has been done using Wilson-clover fermions. In the analysis of these data, we quantify the sensitivity of the results to strategies used for removing excited state contamination and invoke the partially conserved axial current relation between the form factors to choose between them. Our data driven analysis includes removing contributions from multihadron N π states that make significant contributions. Our final results are g A = 1.292 ( 53 ) stat ( 24 ) sys for the axial charge; g S = 1.085 ( 50 ) stat ( 103 ) sys and g T = 0.991 ( 21 ) stat ( 10 ) sys for the scalar and tensor charges; ⟨ r A 2 ⟩ = 0.439 ( 56 ) stat ( 34 ) sys fm 2 for the mean squared axial charge radius, g P * = 9.03 ( 47 ) stat ( 42 ) sys for the induced pseudoscalar charge; and g π N N = 14.14 ( 81 ) stat ( 85 ) sys for the pion-nucleon coupling. We also provide a parametrization of the axial form factor G A ( Q 2 ) over the range 0 ≤ Q 2 ≤ 1 GeV 2 for use in phenomenology and a comparison with other lattice determinations. We find that the various lattice data agree within 10% but are significantly different from the extraction of G A ( Q 2 ) from the ν -deuterium scattering data. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Once-in-a-lifetime encounter models for neutrino media: From coherent oscillations to flavor equilibration

Collective neutrino oscillations are typically studied using the lowest-order quantum kinetic equation, also known as the mean-field approximation. However, some recent quantum many-body simulations suggest that quantum entanglement among neutrinos may be important and may result in flavor equilibration of the neutrino gas. In this work, we develop new quantum models for neutrino gases in which any pair of neutrinos can interact at most once in their lifetimes. A key parameter of our models is γ = μ Δ z , where μ is the neutrino coupling strength, which is proportional to the neutrino density, and Δ z is the duration over which a pair of neutrinos can interact each time. Our models reduce to the mean-field approach in the limit γ → 0 and achieve flavor equilibration in time t ≫ ( γ μ ) − 1 . These models demonstrate the emergence of coherent flavor oscillations from the particle perspective and may help elucidate the role of quantum entanglement in collective neutrino oscillations. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Contour deformations for nonholomorphic actions

We show how contour deformations may be used to control the sign problem of lattice Monte Carlo calculations with nonholomorphic Boltzmann factors. Such actions arise naturally in quantum mechanical scattering problems. The approach is demonstrated in conjunction with the holomorphic gradient flow. As our central example we compute the real-time evolution of a particle in a one-dimensional analog of the Yukawa potential. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗