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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Muon to Positron Conversion

Lepton-flavor violation (LFV) has been discovered in the neutrino sector by neutrino oscillation experiments. The minimal extension of the Standard Model (SM) to include neutrino masses allows LFV in the charged sector (CLFV) at the loop level, but at rates that are too small to be experimentally observed. Lepton-number violation (LNV) is explicitly forbidden even in the minimally extended SM, so the observation of an LNV process would be unambiguous evidence of physics beyond the SM. The search for the LNV and CLFV process μ−+N(A,Z)→e++N′(A,Z−2) (referred to as μ−→e+) complements 0νββ decay searches, and is sensitive to potential flavor effects in the neutrino mass-generation mechanism. A theoretical motivation for μ−→e+ is presented along with a review of the status of past μ−→e+ experiments and future prospects. Special attention is paid to an uncertain and potentially dominant background for these searches, namely, radiative muon capture (RMC). The RMC high energy photon spectrum is theoretically understudied and existing measurements insufficiently constrain this portion of the spectrum, leading to potentially significant impacts on current and future μ−→e+ work.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Theory Summary at Strangeness in Quark Matter 2019

This is the theory summary of Strangeness in Quark Matter 2019 conference. Here, results include the state-of-the-art updates to the Quantum Chromodynamics (QCD) phase diagram with contributions both from heavy-ion collisions and nuclear astrophysics, studies on the QCD freeze-out lines, and several aspects regarding small systems including collectivity, heavy flavor dynamics, strangeness, and hard probes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

A fragmentation approach to jet flavor

An intuitive definition of the partonic flavor of a jet in quantum chromodynamics is often only well-defined in the deep ultraviolet, where the strong force becomes a free theory and a jet consists of a single parton. However, measurements are performed in the infrared, where a jet consists of numerous particles and requires an algorithmic procedure to define their phase space boundaries. To connect these two regimes, we introduce a novel and simple partonic jet flavor definition in the infrared. We define the jet flavor to be the net flavor of the partons that lie exactly along the direction of the Winner-Take-All recombination scheme axis of the jet, which is safe to all orders under emissions of soft particles, but is not collinear safe. Collinear divergences can be absorbed into a perturbative fragmentation function that describes the evolution of the jet flavor from the ultraviolet to the infrared. The evolution equations are linear and a small modification to traditional DGLAP and we solve them to leading-logarithmic accuracy. The evolution equations exhibit fixed points in the deep infrared, we demonstrate quantitative agreement with parton shower simulations, and we present various infrared and collinear safe observables that are sensitive to this flavor definition.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Measurement of the B s 0 → μ + μ - decay properties and search for the B 0 → μ + μ - and B s 0 → μ + μ - γ decays

An improved measurement of the decay $B^0_S$ → $μ^+μ^-$ and searches for the decays $B^0$ → $μ^+μ^+$ and $B^0_S$ → $μ^+μ^-γ$ are performed at the LHCb experiment using data collected in proton-proton collisions at $\sqrt{s}$ = 7, 8 and 13 TeV. corresponding to integrated luminosities of 1, 2 and 6 fb -1 , respectively. The $B^0_S$ → $μ^+μ^-$ branching fraction and effective lifetime are measured to be $\mathscr{B}$($B^0_S$ → $μ^+μ^-$) = (3.09$^{(+0.46+0.15)}_{(-0.43-0.11)}$) x 10 -9 and $τ(B^0_s →μ^+μ^-)$ = (2.07 ± 0.29 ± 0.03) ps, respectively, where the uncertainties include both statistical and systematic contributions. No significant signal for $B^0$ → $μ^+μ^-$ and $B^0_S$ → $μ^+μ^-γ$ decays is found and the upper limits $\mathscr{B}$($B^0$ → $μ^+μ^-$) < 2.6 x 10 -10 and $B^0_S$ → $μ^+μ^-γ$ < 2.0 x 10 -9 at 95% confidence level are determined, where the latter is limited to the range $m_{μμ}$ > 4.9 GeV/c 2 . Additionally, the ratio between the $B^0$ → $μ^+μ^-$ and $B^0_S$ → $μ^+μ^-$ branching fractions is measured to be $\mathscr{R}_{μ+μ-}$ < 0.095 at 95% confidence level. The results are in agreement with the Standard Model predictions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

First Measurement of Deeply Virtual Compton Scattering on the Neutron with Detection of the Active Neutron

Measuring deeply virtual Compton scattering (DVCS) on the neutron is one of the necessary steps to understand the structure of the nucleon in terms of generalized parton distributions (GPDs). Neutron targets play a complementary role to transversely polarized proton targets in the determination of the GPD E . This poorly known and poorly constrained GPD is essential to obtain the contribution of the quarks’ angular momentum to the spin of the nucleon. DVCS on the neutron was measured for the first time selecting the exclusive final state by detecting the neutron, using the Jefferson Lab longitudinally polarized electron beam, with energies up to 10.6 GeV, and the CLAS12 detector. The extracted beam-spin asymmetries, combined with DVCS observables measured on the proton, allow a clean quark-flavor separation of the imaginary parts of the Compton form factors H and E . Published by the American Physical Society 2024

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

𝐵 → 𝜌⁢ℓ⁢$\bar{v}$ Resonance Form Factors from 𝐵→ 𝜋⁢𝜋⁢ℓ⁢$\bar{v}$ in Lattice QCD

The decay 𝐵 → 𝜌⁢ℓ⁢$\bar{v}$ is an attractive process for determining the magnitude of the smallest Cabibbo-Kobayashi-Maskawa matrix element, |𝑉 𝑢⁢𝑏 |, and can provide new insights into the origin of the long-standing exclusive-inclusive discrepancy in determinations of this standard-model parameter. This requires a nonperturbative QCD calculation of the 𝐵 → 𝜌 form factors 𝑉, 𝐴 0 , 𝐴 1 , and 𝐴 12 . The unstable nature of the 𝜌 resonance has prevented precise lattice QCD calculations of these form factors to date. Here, we present the first lattice QCD calculation of the 𝐵 → 𝜌 form factors in which the 𝜌 is treated properly as a resonance in 𝑃-wave 𝜋⁢𝜋 scattering. To this end, we use the Lellouch-Lüscher finite-volume formalism to compute the 𝐵 → 𝜋⁢𝜋 form factors as a function of both momentum transfer and 𝜋⁢𝜋 invariant mass, and then analytically continue to the 𝜌 resonance pole. This calculation is performed with 2 + 1 dynamical quark flavors at a pion mass of approximately 320 MeV, and demonstrates a clear path toward results at the physical point.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2023

Improved Fermion Hamiltonians for Quantum Simulation

The Symanzik improvement program has been quite successful in classical simulations of quantum chromodynamics allowing calculations to be performed at coarser lattice spacings and with reduced computational resource costs. It is expected that improved Hamiltonians will be essential to simulate lattice field theories using quantum computers. In this work I will discuss the formulation of an ASQTAD and HISQ Hamiltonian amenable for quantum simulations. I will also show preliminary results that demonstrate significant tree-level contributions are removed in the spectrum of the 1 flavor Schwinger model.

quantum computing↗