Wed·Jul 24, 2019Wednesday·July 24, 2019

1. 01*

   New Insight in the $Q^2$-Dependence of Proton Generalized Polarizabilities

   J. Beričič (1) · L. Correa (2)(3) · M. Benali (2) · P. Achenbach (3) · C. Ayerbe Gayoso (3) · J.C. Bernauer (4)(5) · A. Blomberg (5) · R. Böhm (3) · D. Bosnar (6) · L. Debenjak (1) · A. Denig (3) · M.O. Distler (3) and 27 other authors

   Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer $Q^2$: 0.10, 0.20 and 0.45 GeV${}^2$, at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion relations allowed the extraction of the structure functions $P_{LL}-P_{TT}/ϵ$ and $P_{LT}$, as well as the electric and magnetic generalized polarizabilities ${\alpha }_{E1}(Q^2)$ and ${\beta }_{M1}(Q^2)$. These new results show a smooth and rapid fall-off of ${\alpha }_{E1}(Q^2)$, in contrast to previous measurements at $Q^2$ = 0.33 GeV${}^2$, and provide for the first time a precise mapping of ${\beta }_{M1}(Q^2)$ in the low-$Q^2$ region.

   nucl-exPRL(2019)·15 citations
2. 02*

   Non-adiabatic transitions and non-equilibrium statistics of deforming nuclei

   Nishchal R. Dwivedi · Sudhir R. Jain🇮🇳

   We establish a connection between macroscopic "heating or cooling" of a finite many-body quantum system and the non-adiabatic Landau-Zener-Stückelberg transitions between its quantum states. We have considered the well-known Nilsson model for describing the single-particle states of nuclei and subject the system to a random walk in the deformation space. This subsumes modelling of an evolving many-body system where the dynamics is chaotic. We discover a universality in the distribution of final "temperatures", beginning with a canonical equilibrium at some temperature $T$. The quantum system is thrown out of equilibrium where free energy and work undergo fluctuations. These fluctuations are shown to respect Jarzynski inequality, and, the Bochkov-Kuzovlev equalities. We believe that this study will pave the way towards understanding non-equlibrium phenomena in other finite quantum systems like metallic clusters, quantum dots, and others.

   ↳ nucl-thnlin.CDnucl-ex0 citations
3. 03*

   Trees and Islands -- Machine learning approach to nuclear physics

   Nishchal R. Dwivedi

   We implement machine learning algorithms to nuclear data. These algorithms are purely data driven and generate models that are capable to capture intricate trends. Gradient boosted trees algorithm is employed to generate a trained model from existing nuclear data, which is used for prediction for data of damping parameter, shell correction energies, quadrupole deformation, pairing gaps, level densities and giant dipole resonance for large number of nuclei. We, in particular, predict level density parameter for superheavy elements which is of great current interest. The predictions made by the machine learning algorithm is found to have standard deviation from 0.00035 to 0.73.

   ↳ nucl-thcs.LGnucl-exstat.ML1 citation
4. 04*

   Ignatyuk damping factor: A semiclassical formula

   Nishchal R. Dwivedi · Saniya Monga · Harjeet Kaur · Sudhir R. Jain🇮🇳

   Data on nuclear level densities extracted from transmission data or gamma energy spectrum store the basic statistical information about nuclei at various temperatures. Generally this extracted data goes through model fitting using computer codes like CASCADE. However, recently established semiclassical methods involving no adjustable parameters to determine the level density parameter for magic and semi-magic nuclei give a good agreement with the experimental values. One of the popular ways to paramaterize the level density parameter which includes the shell effects and its damping was given by Ignatyuk. This damping factor is usually fitted from the experimental data on nuclear level density and it comes around 0.05 $Me{V}^{-1}$. In this work we calculate the Ignatyuk damping factor for various nuclei using semiclassical methods.

   ↳ nucl-thnucl-exIJMPE(2019)·10 citations
5. 05*

   Novel chiral Hamiltonian and observables in light and medium-mass nuclei

   V. Somà🇫🇷 · P. Navrátil🇨🇦 · F. Raimondi🇬🇧 · C. Barbieri🇬🇧 · T. Duguet🇫🇷

   A novel parameterisation of a Hamiltonian based on chiral effective field theory is introduced. Specifically, three-nucleon operators at next-to-next-to-leading order are combined with an existing (and successful) two-body interaction containing terms up to next-to-next-to-next-to-leading order. The resulting potential is labelled $NN$+$3N\text{(lnl)}$. The objective of the present work is to investigate the performance of this new Hamiltonian across light and medium-mass nuclei. Binding energies, nuclear radii and excitation spectra are computed using no-core shell model and self-consistent Green's function approaches. Calculations with $NN$+$3N\text{(lnl)}$ are compared to two other representative Hamiltonians currently in use, namely NNLO${}_{\text{sat}}$ and the older $NN$+$3N(400)$. Overall, the performance of the novel interaction is very encouraging. In light nuclei, total energies are generally in good agreement with experimental data. Known spectra are also well reproduced with a few notable exceptions. The good description of ground-state energies carries on to heavier nuclei, all the way from oxygen to nickel isotopes. Except for those involving excitation processes across the $N=20$ gap, which is overestimated by the new interaction, spectra are of very good quality, in general superior to those obtained with NNLO${}_{\text{sat}}$. Although largely improving on $NN$+$3N(400)$ results, charge radii calculated with $NN$+$3N\text{(lnl)}$ still underestimate experimental values, as opposed to the ones computed with NNLO${}_{\text{sat}}$ that successfully reproduce available data on nickel. On the whole, the new two- plus three-nucleon Hamiltonian introduced in the present work represents a promising alternative to existing nuclear interactions.

   ↳ nucl-thnucl-exPRC(2020)·201 citations
6. 06*

   Compton Scattering Energy Spectrum for Si and Ge Systems

   Chen-Kai Qiao🇨🇳 · Hsin-Chang Chi🇹🇼 · Shin-Ted Lin🇨🇳 · Peng Gu🇨🇳 · Shu-Kui Liu🇨🇳 · Chang-Jian Tang🇨🇳

   In the present work, we study the atomic Compton Scattering which could have great impacts on dark matter direct detection experiments. We give a quantitative analysis of the Compton scattering energy spectrum for Si and Ge atomic systems. The theoretical results on Compton scattering are calculated within the frameworks of free electron approximation (FEA) and relativistic impulse approximation (RIA). The low-energy transfer and near photoionization threshold regions are especially considered in this work. In RIA calculation, to obtain the atomic ground states, we adopt an \emph{ab initio} calculation in the fully relativistic Dirac-Fock theory.

   ↳ physics.atom-phhep-exnucl-exPhysics(2020)·8 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.