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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Intrinsic Transverse Motion of the Pion’s Valence Quarks

Starting with the solution to the Bethe-Salpeter equation for the pion, in a beyond rainbow-ladder truncation to QCD's Dyson-Schwinger equations, we determine the pion's $\mathcal{l}$ z = 0 and |$\mathcal{l}$ z | = 1 leading Fock-state light-front wave functions (LFWFs) [labeled by $\psi$ $\mathcal{l}$ z ($\mathcal{x}$, $\mathcal{k}$$2\atop{T}$)]. The leading-twist time-reversal even transverse momentum dependent parton distribution function (TMD) of the pion is then directly obtained using these LFWFs. A key characteristic of the LFWFs, which is driven by dynamical chiral symmetry breaking, is that at typical hadronic scales they are broad functions in the light-cone momentum fraction $\mathcal{x}$. The LFWFs have a nontrivial ($\mathcal{x}$, $\mathcal{k}$$2\atop{T}$)) dependence and in general do not factorize into separate functions of each variable. For $\mathcal{k}$$2\atop{T}$ ≲ 1 GeV 2 the $\mathcal{k}$$2\atop{T}$ dependence of the LFWFs is well described by a Gaussian; however for $\mathcal{k}$$2\atop{T}$ ≳ 10 GeV 2 these LFWFs behave as $\psi$ 0 ∝ $\mathcal{x}$(1 - $\mathcal{x}$)/$\mathcal{k}$$2\atop{T}$ and $\psi$ 1 ∝ $\mathcal{x}$(1 - $\mathcal{x}$)/$\mathcal{k}$$4\atop{T}$ and therefore exhibit the power-law behavior predicted by perturbative QCD. The pion's TMD naturally inherits many features from the LFWFs. With this being said, the TMD evolution of our result is studied using both the b* and $\zeta$ prescriptions which allows a qualitative comparison with Drell-Yan data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Neutron Valence Structure from Nuclear Deep Inelastic Scattering

Mechanisms of spin-flavor SU(6) symmetry breaking in Quantum Chromodynamics (QCD) are studied via an extraction of the free neutron structure function from a global analysis of deep inelastic scattering (DIS) data on the proton and on nuclei from $A = 2$ (deuterium) to 208 (lead). Modification of the structure function of nucleons bound in atomic nuclei (known as the EMC effect) are consistently accounted for within the framework of a universal modification of nucleons in short-range correlated (SRC) pairs. Our extracted neutron-to-proton structure function ratio $F_2^n/F_2^p$ becomes constant for $x_B \ge 0.6$, equalling $0.47 \pm 0.04$ as $x_B \rightarrow 1$, in agreement with theoretical predictions of perturbative QCD and the Dyson Schwinger equation, and in disagreement with predictions of the Scalar Diquark dominance model. Finally, we also predict $F_2^{^3\mathrm{He}}/F_2^{^3\mathrm{H}}$, recently measured, yet unpublished, by the MARATHON collaboration, the nuclear correction function that is needed to extract $F_2^n/F_2^p$ from $F_2^{^3\mathrm{He}}/F_2^{^3\mathrm{H}}$, and the theoretical uncertainty associated with this extraction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Iridium valence variation and carrier sign tuning in ( Ca , Ba ) x La 2 – x CuIrO 6 double perovskites

Here, we report the structure and properties of ( Ca , Ba ) x La 2 – x CuIrO 6 . The rock-salt double perovskite structure goes through a P 1 ¯ to P 2 1 / n phase transition with increasing Ba content but not with Ca content. In both cases, the Ir ion is oxidized from 4 + to 5 + with increasing substitution. Transport and magnetic properties measurements reveal that all compositions are insulating with hysteretic spin-freezing magnetic behavior. Seebeck coefficient measurements reveal a large thermopower change from + 176 μ V /K in La 2 CuIrO 6 to – 223 μ V /K with increasing Ba content in Ba x La 2 – x CuIrO 6 . This behavior is modeled well by the Heikes formula for correlated hopping conduction. ( Ca , Ba ) x La 2 – x CuIrO 6 provides a model system for investigations of other systems with similar carrier sign tuning, with applications toward semiconductors and thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Observing the effects of numbers of valence nucleons on 0$^{+}_{𝑔⁡𝑠}$ → 2$^{+}_{1}$ transitions in deformed nuclei by comparing proton and neutron transition matrix elements

We examined the ratios of neutron and proton transition matrix elements, 𝑀 𝑛 /𝑀 𝑝 , for the 0$^{+}_{𝑔⁡𝑠}$ → 2$^{+}_{1}$ transitions in 48 even-even stable nuclei with 𝑁 > 20 for which electromagnetic matrix elements were compiled by Pritychenko et al. and for which high-quality inelastic proton-scattering data were available. Several deformed rare-earth nuclei have (𝑀 𝑛 /𝑀 𝑝 )/(𝑁/𝑍) values significantly below 1.0, which is not consistent with a simple liquid-drop picture. However, this phenomenon can be explained using a schematic picture in which 𝑀 𝑝 reaches a maximum at proton midshell (𝑍 = 66) and 𝑀𝑛 reaches its maximum at neutron midshell (𝑁 = 104). Several midmass vibrational nuclei have 𝑀 𝑛 /𝑀 𝑝 values significantly below 𝑁/𝑍, which is not consistent with the expectation that 𝑀 𝑛 /𝑀 𝑝 = 𝑁/𝑍 in such nuclei. As a result, a shell-model investigation of these observations might yield insights about this behavior.

Collective levels↗
DOE OSTI2018

Biexciton Binding Energy in Spherical Quantum Dots with Γ{sub 8} Valence Band

The biexciton binding energy in spherical CdSe/ZnSe quantum dots is calculated variationally in the framework of kp-perturbation theory. Smooth and abrupt confining potentials with the same localization area of carriers are compared for two limiting cases of light hole to heavy hole mass ratio β = m{sub lh}/m{sub hh}: β = 1 and β = 0. Accounting for correlations between carriers results in their polarized configuration and significantly increases the biexciton binding energy in comparison with the first order perturbation theory. For β = 0 in smooth confining potentials there are three nearby biexciton states separated by small energy gap between 1S{sub 3/2} and 1P{sub 3/2} hole states.

36 MATERIALS SCIENCE↗