Nuclear Theory·nucl-th

Monday·November 1, 2021

8 papers—5 primary·3 cross-listed

01
Removing center of mass effects in response function and sum rule calculations based on the harmonic oscillator basis
K. Akdogan · D. Layh · I. Weinberger · J. Simonis · N. Barnea · S. Bacca
Response functions are at the heart of any comparison of theory with experiment in studies of the nuclear dynamics with electroweak probes. Calculations performed in the laboratory frame often suffer from center of mass contaminations that need to be removed. By confining the system in a harmonic oscillator, we derive a set of analytical formulas to subtract the center of mass effects from calculations of response functions and associated sum rules. After a general analytical derivation, we first deal specifically with the longitudinal response function appearing in electron scattering and provide expressions for the center of mass correcting functions. Next, we present a proof of principle study for the case of the electric dipole sum rules in a two-body problem with a numerical implementation of our formalism. These steps pave the way to applying the proposed method to heavier nuclei in the future.
nucl-thPRC(2022)·0 citations
02
Anomalous spin polarization from turbulent color fields
Berndt Müller🇺🇸 · Di-Lun Yang🇹🇼
We study the important, yet widely overlooked, role of gluons for spin transport with a connection to local parity violation in quark gluon plasmas. We employ the formalism of quantum kinetic theory to quarks in weakly coupled quantum chromodynamics to derive the source terms for quark spin polarization. These source terms involve parity-odd correlators of dynamically generated color fields in near-equilibrium quark gluon plasmas and give rise to locally fluctuating axial charge currents. Our results provide a possible explanation for the spin alignment of vector mesons measured in high-energy nuclear collisions.
nucl-thhep-phhep-thPRD(2022)·74 citations
03
Multi-reference many-body perturbation theory for nuclei I -- Novel PGCM-PT formalism
Mikael Frosini🇫🇷 · Thomas Duguet🇫🇷 · Jean-Paul Ebran🇫🇷 · Vittorio Somà🇫🇷
Perturbative and non-perturbative expansion methods already constitute a tool of choice to perform ab initio calculations over a significant part of the nuclear chart. In this context, the categories of accessible nuclei directly reflect the class of unperturbed state employed in the formulation of the expansion. The present work generalizes to the nuclear many-body context the versatile method of Ref. \cite{burton20a} by formulating a perturbative expansion on top of a multi-reference unperturbed state mixing deformed non-orthogonal Bogoliubov vacua, i.e. a state obtained from the projected generator coordinate method (PGCM). Particular attention is paid to the part of the mixing taking care of the symmetry restoration, showing that it can be exactly contracted throughout the expansion, thus reducing significantly the dimensionality of the linear problem to be solved to extract perturbative corrections. While the novel expansion method, coined as PGCM-PT, reduces to the PGCM at lowest order, it reduces to single-reference perturbation theories in appropriate limits. Based on a PGCM unperturbed state capturing (strong) static correlations in a versatile and efficient fashion, PGCM-PT is indistinctly applicable to doubly closed-shell, singly open-shell and doubly open-shell nuclei. The remaining (weak) dynamical correlations are brought consistently through perturbative corrections. This symmetry-conserving multi-reference perturbation theory is state-specific and applies to both ground and excited PGCM unperturbed states, thus correcting each state belonging to the low-lying spectrum of the system under study.
nucl-thEPJA(2022)·73 citations
04
Bayesian reconstruction of nuclear matter parameters from the equation of state of neutron star matter
Sk Md Adil Imam🇮🇳 · N. K. Patra🇮🇳 · C. Mondal🇫🇷 · Tuhin Malik🇵🇹 · B. K. Agrawal🇮🇳
The nuclear matter parameters (NMPs), those underlie in the construction of the equation of state (EoS) of neutron star matter, are not directly accessible. The Bayesian approach is applied to reconstruct the posterior distributions of NMPs from the EoS of neutron star matter. The constraints on lower-order parameters as imposed by the finite nuclei observables are incorporated through appropriately chosen prior distributions. The calculations are performed with two sets of pseudo data on the EoS whose true models are known. The median values of second or higher order NMPs show sizeable deviations from their true values and associated uncertainties are also larger. The sources of these uncertainties are intrinsic in nature, identified as (i) the correlations among various NMPs and (ii) the variations in the EoS of symmetric nuclear matter, symmetry energy, and the neutron-proton asymmetry in such a way that the neutron star matter EoS remain almost unaffected.
nucl-thastro-ph.IMphysics.comp-phPRC(2022)·39 citations
05
Large- $N_{c}$ constraints for elastic dark matter-light nucleus scattering in pionless effective field theory
Thomas R. Richardson🇺🇸 · Xincheng Lin🇺🇸 · Son T. Nguyen🇺🇸
Recent proposals for the use of light nuclei as dark matter direct detection targets necessitate a strong theoretical understanding of the nuclear physics involved. We perform relevant calculations for dark matter-light nucleus scattering in a combined pionless effective field theory and large- $N_{c}$ expansion, where $N_{c}$ is the number of quark colors. We include a general set of one-nucleon currents that have been used in other effective theories, as well as novel two-nucleon contact currents. First, we obtain constraints for the relative sizes of the dark matter couplings to the one- and two-nucleon currents through the large- $N_{c}$ expansion. Then, we use these constraints to make predictions for the relative sizes of spin-dependent and spin-independent cross sections for dark matter scattering off of a nucleon, a deuteron, a triton, and helium-3.
nucl-thhep-phPRC(2022)·9 citations
06
Suppression of thermal vorticity as an indicator of QCD critical point
Sushant K. Singh🇮🇳 · Jan-e Alam🇮🇳
We study the impact of the QCD critical point (CP) on the spin polarization of $Λ$ -hyperon generated by the thermal vorticity in viscous quark gluon plasma (QGP). The equations of the relativistic causal viscous hydrodynamics have been solved numerically in (3+1) dimensions to evaluate the thermal vorticity. The effects of the CP have been incorporated through the equation of state (EoS) and the scaling behavior of the transport coefficients. A significant reduction in the global polarization has been found as the CP is approached. A drastic change induced by the CP in the rapidity dependence of the spin polarization is observed which can be used as a signature of the CP.
↳ hep-phhep-exnucl-thEPJC(2023)·19 citations
07
Measurement of Compton scattering at MAMI for the extraction of the electric and magnetic polarizabilities of the proton
A2 Collaboration: E. Mornacchi (1) · P.P. Martel (1 and 2) · S. Abt (3) · P. Achenbach (1) · P. Adlarson (1) · F. Afzal (4) · Z. Ahmed (5) · J.R.M. Annand (6) · H.J. Arends (1) · M. Bashkanov (7) · R. Beck (4) · M. Biroth (1) and 53 other authors
A precise measurement of the differential cross-sections $d σ / d Ω$ and the linearly polarized photon beam asymmetry $Σ_{3}$ for Compton scattering on the proton below pion threshold has been performed with a tagged photon beam and almost $4 π$ detector at the Mainz Microtron. The incident photons were produced by the recently upgraded Glasgow-Mainz photon tagging facility and impinged on a cryogenic liquid hydrogen target, with the scattered photons detected in the Crystal Ball/TAPS set-up. Using the highest statistics Compton scattering data ever measured on the proton along with two effective field theories (both covariant baryon and heavy-baryon) and one fixed- $t$ dispersion relation model, constraining the fits with the Baldin sum rule, we have obtained the proton electric and magnetic polarizabilities with unprecedented precision: \begin{align*} &{}\alpha_{E1} = 10.99 \pm 0.16 \pm 0.47 \pm 0.17 \pm 0.34 &{}\beta_{M1} = 3.14 \pm 0.21 \pm 0.24 \pm 0.20 \pm 0.35 \end{align*} in units of $1 0^{- 4}$ \,fm $^{3}$ where the errors are statistical, systematic, spin polarizability dependent and model dependent.
↳ nucl-exnucl-thPRL(2022)·22 citations
08
CME search at STAR
Yu Hu (for the STAR Collaboration)🇨🇳
The hot and dense medium produced in relativistic heavy-ion collisions has been conjectured to be accompanied by an axial charge asymmetry that may lead to a separation of electric charges in the direction of the extremely strong magnetic field, also known as the Chiral Magnetic Effect (CME). The measurement of azimuthal correlator ( $Δ γ$ ) with respect to the spectator plane, gives us an opportunity to measure the possible CME fraction beyond the flow background. Preliminary results using this approach with combined Au+Au collisions at $s_{N N} =$ 200 GeV and U+U at $s_{N N} =$ 193 GeV show $f_{C M E}$ at $(8 \pm 4 \pm 8)$ $%$ . Meanwhile, the observability of CME has been conjectured to be dependent on $s_{N N}$ due to changes in the lifetime of the magnetic field, the strengths of CME signal and non-CME background. At lower energies, the Event Plane Detector (EPD) installed in the year 2018 provides a unique capability for CME search. The background scenario test at Au+Au $s_{N N} =$ 27 GeV by using $Δ γ$ with respect to TPC and the new installed EPD shows a consistency with no-CME scenario in the current statistics. The method of the ongoing isobar blind analysis, and the latest sensitivity check with the event-by-event AVFD model on the different observables between Ru+Ru and Zr+Zr are also briefly discussed.
↳ nucl-exhep-phnucl-thEPJ Web Conf.(2022)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE