Session NF: Theory: DIS/ew-Nucleon/ Light Nuclei/ In medium/ Classical

Regge model of NN scattering amplitudes and its application to describe final state interactions in $^2H(e,e'p)$

A Regge model to parametrize NN scattering amplitudes has been developed for $s>5.4$ GeV $^2$. The model is fully relativistic and includes all spin dependence. The parameters of the model were fit to available NN scattering observables. Application of the model to describe final state interactions in deuteron electrodisintegration are presented.   

The Similarity Renormalization Group for Three-Body Bound State; A Three-Dimensional Approach

Similarity renormalization group (SRG) evolution of two- and three-body interactions is studied in a three-dimensional (3D) momentum representation. The SRG flow equations are formulated as a function of momentum vector variables, without using the partial wave (PW) representation. The non-PW form of SRG evolved two- and three-body interactions, obtained from spin-independent interactions, are used to solve the Faddeev integral equations for the bound state in 3D. The dependence of the binding energy on the flow parameter of the evolved two-and three-body interactions is investigated and properties of wave function are studied as function of the SRG evolution.   

Electromagnetic structure of A=2 and 3 nuclei in chiral effective field theory

The objective of this presentation is to provide a complete set of $\chi$EFT predictions for the structure functions and tensor polarization of the deuteron, for the charge and magnetic form factors of $^3$He and $^3$H, and for the charge and magnetic radii of these few-nucleon systems. The calculations use wave functions derived from high-order chiral two- and three-nucleon potentials and Monte Carlo methods to evaluate the relevant matrix elements. Predictions based on conventional potentials in combination with $\chi$EFT charge and current operators are also presented. There is excellent agreement between theory and experiment for all these observables for momentum transfers up to $q \leq 2.0-2.5$ fm$^{-1}$.   

Momentum Distributions for the Masses

We report variational Monte Carlo calculations of single-nucleon momentum distributions for $A \leq 12$ nuclei. The wave functions have been generated for the Argonne v$_{18}$ two-nucleon and Urbana X three-nucleon potentials. The distributions exhibit a high-momentum tail attributable to the one-pion-exchange tensor interaction and are proportional to the deuteron tail. They are broken down into spin and isospin components which may give insight into polarization and halo aspects of different nuclei. We also present some cluster distributions, such as $d$-$p$ in $^3$He, $t$-$p$ in $^4$He, and $\alpha$-$t$ in $^7$Li. These momentum distributions are made available on-line at www.phy.anl.gov/theory/research/momenta/ as both tables and figures.   

Electromagnetic transitions in $A \leq 10$ nuclei including two-body $\chi$EFT currents

Recently, we presented ab initio quantum Monte Carlo calculations of magnetic moments and M1 transitions in A $\leq$ 9 nuclei, which include two-body chiral effective field theory meson exchange current contributions. The latter are found to always improve the theoretical predictions leading to a very good agreement with the experimental data. Here, we report on a preliminary study, carried out within the same framework, of electroweak transitions in additional A = 8 and A = 10 nuclear systems, with emphasis on transitions involving the isospin mixed states in $^8$Be at $\sim$16 MeV.   

Quasi-Classical Origins of Single Transverse Spin Asymmetries

We consider semi-inclusive deep inelastic scattering and the Drell-Yan process on a transversely-polarized proton at high energies. We model the small-$x$ wave function of the proton using the McLerran-Venugopalan (MV) model, which has been reasonably successful in describing high-energy proton data. The MV model, originally formulated for a heavy ion with a large number $\sim A$ of independent color charges, is a quasi-classical description that should apply to any dense system of color charges, including a proton at very high energies. Here we incorporate spin dependence into the MV framework and analyze several microscopic scattering channels that lead to the generation of a single transverse spin asymmetry. In particular, we study asymmetries mediated by intrinsic orbital angular momentum, asymmetries produced locally by rescattering on the same constituent, and asymmetries that couple to the odderon. This analysis yields a simple, intuitive, quasi-classical picture in which one can understand understand the famous sign-reversal of the Sivers asymmetry between semi-inclusive deep inelastic scattering and the Drell-Yan process.   

In-Medium Similarity Renormalization Group studies of nuclear matter

Ab initio calculations of infinite matter are crucial for both density functional theory and predictions of neutron star properties. The In-Medium Similarity Renormalization Group (IM-SRG) has recently been applied successfully to several finite nuclei. The method's polynomial scaling and its ability to handle non-local interactions make it a good method for calculating infinite matter. Promising results for a one-dimensional model of nuclear matter are discussed, with special emphasis on the ability to include three-body forces in a computationally efficient manner.   

Low Energy Nuclear Reactions w/o Tunnelling Explained

Using the phenomenon of nuclear vibration low energy nuclear reactions can be explained using classical mechanics. Consider an incoming positive charge such as a proton approaching a vibrating nucleus. If he amplitudes of nuclear oscillation are equal in all directions, the position of the incoming positive charge is $r=[(x + AcosX)^2 + (y+AcosY)^2 + (z+AcosZ)^2]^{1/2}$. Then the KE needed (barrier height) is $KE=kQ_1`Q_2/r.$ If the nucleus is considered as point nucleus, and the contact point is $x=AcosX, y=AcosY$ and $z=AcosZ,$ KE needed is $KE=kQ_1Q_2/[(2AcosX)^2 +(2AcosY)^2 +(2AcosZ)^2]^{1/2}$. Collecting terms KE needed is $KE=kQ_1Q_2/(12A^2cos^2B)^{1/2}$ if all the cosines are equal. Therefore, the barrier height for an oscillating nucleus with incoming positive charge is $KE=kQ_1Q_2/(3.46AcosB.)$ If $RMScos =0.707$, the average barrier height is $KE= kQ_1Q_2/2.45A$, where A is the average amplitude of nuclear of vibration. In deuterium-deuterium fusion occurring on the sun, the temperature needed is $4.0x10^7K$. The nuclear barrier height to be overcome is $8.286x10^{-15}$j using the equipartition of energy formula $1/2mv^2=3/2kT.$ Solving for A, the average amplitude of vibration needed for two deuterium nuclei to fuse is approx. $11.33$ fermis.