Nuclear Theory·nucl-th

Monday·April 1, 2019

8 papers—3 primary·5 cross-listed

01
The Schwinger Scattering of Twisted Neutrons by Nuclei
Andrei V. Afanasev · D.V. Karlovets · V.G. Serbo
Thanks to J.~Schwinger, the process of elastic scattering of neutrons by nuclei is known to depend on the interference between a nuclear amplitude and an electromagnetic one for small scattering angles, resulting in spin asymmetries of a cross section or in polarization of the scattered neutrons. While this interference depends on the neutron's {\it transverse} polarization and on {\it an imaginary part} of the nuclear amplitude, this conclusion holds only for the incident plane-wave neutrons with a definite momentum. Here we show that this scattering is altered when the twisted neutrons, recently obtained experimentally, are used instead -- that is, neutrons with an orbital angular momentum. For bulk targets, the angular distributions of the scattered neutrons get modified, while scattering of a superposition of states with the different angular momenta also reveals dependence on the longitudinal polarization. For well-localized targets, the observables develop a dependence on the neutron's {\it helicity} and on {\it a real part} of the nuclear amplitude, providing full access to its phase already in the Born approximation. We argue that the corresponding spin asymmetries are measurable at existing neutron facilities. Thus, scattering of the twisted neutrons by nuclei can provide means for quantum tomography of the neutron states and become a useful tool for hadronic studies, low-energy nuclear physics, tests of fundamental symmetries, and neutron optics.
nucl-thPRC(2019)·31 citations
02
Shape and shell-structure of lighter (N<90) neutron-rich nuclei based on phenomenological Woods-Saxon potential
Ikuko Hamamoto
By using a phenomenologically successful Woods-Saxon potential, I study the shape and shell structure of (A) neutron drip line nuclei with 10 \leq N \leq 60, (B) neutron-rich nuclei related to the r- process with 40 \leq N \leq 90, and (C) one-particle spectra in the potential provided by the nucleus 70Fe as a representative of so-called N=40 "island of inversion (IoI)" nuclei. First, the shell structure that is unique in very weakly-bound neutrons is systematically studied, and the approximate neutron number of odd-N nuclei at which spherical (or deformed) halos can be found is pinned down. Second, the difference of the shell structure in r-process nuclei from that in stable nuclei is examined. Third, the similarity and the difference between the shell structure of N=20 IoI nuclei and that of N=40 IoI nuclei are analyzed. As a result of it, it is concluded that in Fe and Cr isotopes the deformation called "N=40 IoI" continuing up to N=50 is unlikely.
nucl-thPRC(2019)·8 citations
03
Ab initio short-range-correlation scaling factors from light to medium-mass nuclei
J. E. Lynn🇩🇪 · D. Lonardoni🇺🇸 · J. Carlson🇺🇸 · J.-W. Chen🇹🇼 · W. Detmold🇺🇸 · S. Gandolfi🇺🇸 · A. Schwenk🇩🇪
High-energy scattering processes, such as deep inelastic scattering (DIS) and quasielastic (QE) scattering provide a wealth of information about the structure of atomic nuclei. The remarkable discovery of the empirical linear relationship between the slope of the European Muon Collaboration (EMC) effect in DIS and the short-range-correlation (SRC) scaling factors $a_{2}$ in QE kinematics is naturally explained in terms of scale separation in effective field theory. This explanation has powerful consequences, allowing us to calculate and predict SRC scaling factors from ab initio low-energy nuclear theory. We present ab initio calculations of SRC scaling factors for a nucleus $A$ relative to the deuteron $a_{2} (A / d)$ and relative to $^{3} He$ $a_{2} (A /^{3} He)$ in light and medium-mass nuclei. Our framework further predicts that the EMC effect and SRC scaling factors have minimal or negligible isovector corrections.
nucl-thnucl-exJ.Phys.G(2020)·36 citations
04
QED radiative corrections for Polarized Lepton-Proton Scattering
Razvan-Daniel Bucoveanu🇩🇪 · Hubert Spiesberger🇩🇪
We discuss QED radiative corrections at first and second order for the parity violating asymmetry $A_{PV}$ in elastic electron proton scattering. A measurement of $A_{PV}$ is planned at low energies and with high precision by the forthcoming P2 experiment at the new MESA facility in Mainz. Bremsstrahlung leads to a shift of the momentum transfer $Q^{2}$ which affects the determination of the weak charge of the proton.
↳ hep-phnucl-thPoS(2019)·5 citations
05
Theoretical study on \eta'--> 4 pions
Ehsan Jafari🇺🇸 · Bing An Li🇺🇸
The $η^{'}$ meson is associated with the U(1) anomaly. In this paper, a successful effective chiral theory of mesons has been applied to study the anomalous decay of $η^{'} \to π^{+} π^{-} π^{+ (0)} π^{- (0)}$ . In this study, the contributions of triangle and box anomalies are calculated. It is shown that the contribution of box diagrams is important in this process. We predict branching ratios of $B r (η^{'} \to π^{+} π^{-} π^{+} π^{-}) = \frac{1}{2} B r (η^{'} \to π^{+} π^{-} π^{0} π^{0}) = (8.3 \pm 1.2) \times 1 0^{- 5}$ , which is in good agreement with BESIII measurement.
↳ hep-phnucl-thNPB(2021)·0 citations
06
Renormalization of Unitarized Weinberg-Tomozawa Interaction without On-shell Factorization and $I = 0$ $K ˉ N$ - $π Σ$ Coupled Channels
Osamu Morimatsu🇯🇵 · Kazuki Yamada🇯🇵
We calculate the scattering $T$ -matrix of $I = 0$ $K ˉ N - π Σ$ coupled channels taking a ladder sum of the Weinberg-Tomozawa interaction without on-shell factorization, regularizing three types of divergent meson-baryon loop functions by dimensional regularization and renormalizing them by introducing counter terms. We show that not only infinite but also finite renormalization is important in order for the renormalized physical scattering $T$ -matrix to have the form of the Weinberg-Tomozawa interaction. The results with and without on-shell factorization are compared. The difference of the scattering $T$ -matrix is small near the renormalization point, close to the observed $Λ$ (1405). The difference, however, increases with the distance from the renormalization point. The scattering $T$ -matrix without on-shell factorization has two poles in the complex center-of-mass energy plane as with on-shell factorization, the real part of which is close to the observed $Λ$ (1405). While the difference is small with and without on-shell factorization in the position of the first pole, closer to the observed $Λ$ (1405), the difference is considerably large in the position of the second pole: the imaginary part of the center-of-mass energy of the second pole without on-shell factorization is as large as or even larger than twice that with on-shell factorization. Also, we discuss the origin of the contradiction about the second pole between two approaches, the chiral unitary approach with on-shell factorization and the phenomenological approach without on-shell factorization.
↳ hep-phnucl-thPRC(2019)·12 citations
07
Searching for flavor dependence in nuclear quark behavior
J. Arrington🇺🇸 · N. Fomin🇺🇸
The observed correlation between the EMC effect and the contribution of short-range correlations (SRCs) in nuclei suggests that the modification of the quark distributions of bound protons and neutrons might occur within SRCs. This raises the possibility that the EMC effect may have an isospin dependence arising from the np dominance of SRCs. We discuss previous attempts to test this possibility and perform a new analysis of existing data. We find no experimental support for the observation of an isospin dependence of the EMC effect.
↳ nucl-exnucl-thPRL(2019)·27 citations
08
High Density with Elliptic Flows
W. Trautmann
The elliptic flow of emitted particles and fragments observed in heavy-ion reactions at high energy has become an important observable reflecting the pressure generated in the dense collision zone. More recently, the strength of the nuclear symmetry energy has been investigated by measuring the ratios or differences of the elliptic flows exhibited by neutrons and charged particles in 197Au+197Au collisions at 400 MeV/nucleon incident energy at the GSI laboratory. A moderately soft to linear dependence on density was deduced for a range of densities shown to reach beyond twice the saturation value in these experiments. The known sources of uncertainties and possible model dependencies were thoroughly studied with transport models of the UrQMD and Tuebingen QMD type. A new source of information on the nuclear equation of state at high density has opened up with the observation of the first LIGO and Virgo GW170817 gravitational wave signal from a neutron star merger. The quantitative comparison of terrestrial and celestial results on the basis of measured or inferred neutron star radii or core pressures, including those obtained from X-ray observations, reveals a rather satisfactory agreement. Depending on the precision that can be achieved with future measurements and observations, it will thus become possible to assess the validity of the applied models and methods. The perspectives for improved experiments at FAIR using the NeuLAND and KRAB detection systems are outlined.
↳ nucl-exastro-ph.HEnucl-thAIP Conf.Proc.(2019)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE