Nuclear Theory·nucl-th

Wednesday·December 23, 2020

7 papers—3 primary·4 cross-listed

04
Electromagnetic form factors of the $Ω^{-}$ baryon in the spacelike and timelike regions
G. Ramalho🇧🇷
We present complete calculations of the electromagnetic form factors of the $Ω^{-}$ in the spacelike region and in the timelike region. The four elastic form factors: electric charge ( $G_{E 0}$ ), magnetic dipole ( $G_{M 1}$ ), electric quadrupole ( $G_{E 2}$ ) and magnetic octupole ( $G_{M 3}$ ), are estimated within the covariant spectator quark model, in terms of the square momentum transfer $q^{2}$ . The free parameters of the $Ω^{-}$ wave function, including a $S$ -wave state and two independent $D$ -wave states radial wave functions and the admixture coefficients are fixed by the comparison with the lattice QCD data in the spacelike region ( $Q^{2} = - q^{2} \leq 0$ ) and with the recent $e^{+} e^{-} \to Ω^{-} Ω ˉ^{+}$ data from CLEO in the timelike region ( $q^{2} > 0$ ). The estimates in the timelike region for square momentum transfer $q^{2} \geq 4 M_{Ω}^{2}$ are based on large- $q^{2}$ asymptotic relations ( $M_{Ω}$ is the $Ω^{-}$ mass). We examine also the impact of the large- $Q^{2}$ correlations between different form factors and analyze the possible solutions. The electric quadrupole and the magnetic octupole moments of the $Ω^{-}$ , and the $e^{+} e^{-} \to Ω^{-} Ω ˉ^{+}$ integrated cross sections for very large $q^{2}$ are estimated based on the model results.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2021)·22 citations
05
Kinematic Azimuthal Asymmetries and Lam-Tung Relation
O.V. Teryaev🇷🇺
The origin of Lam-Tung relation for the angular asymmetry of Drell-Yan dileptons is analyzed. The asymmetry constrained by this relation is shown to belongto the class of kinematic azimuthal asymmetries, emerging due to the deviation of the reference axis from the natural physical one. The validity and violation of Lam-Tung relation due to radiative and power QCD corrections is discussed. The relation is generalized to the case when the virtual photon is not the transverse oneand the possible applications are suggested.
↳ hep-phnucl-th4 citations
06
Comprehensive test of the Brink-Axel hypothesis in the energy region of the pygmy dipole resonance
M. Markova (1) · P. von Neumann-Cosel (2) · A. C. Larsen (1) · S. Bassauer (2) · A. Görgen (2) · M. Guttormsen (1) · F. L. Bello Garrote (1) · H. C. Berg (1) · M. M. Bjørøen (1) · T. Dahl-Jacobsen (1) · T. K. Eriksen (1) · D. Gjestvang (1) and 13 other authors
The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for 116,120,124Sn below the neutron separation energy by means of three independent experimental methods. The $γ$ -ray strength functions (GSFs) extracted from primary $γ$ -decay spectra following charged-particle reactions with the Oslo method and with the Shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states. The results provide a critical test of the generalized Brink-Axel hypothesis in heavy nuclei, demonstrating its applicability in the energy region of the pygmy dipole resonance.
↳ nucl-exnucl-thPRL(2021)·27 citations
07
Formation of light (anti)nuclei
J. Tjemsland🇳🇴
The production mechanism of light nuclei, such as deuteron, helium-3, tritium and their antiparticles, has recently attracted an increased attention from the astroparticle and heavy ion communities. The expected low astrophysical background of light antinulei makes them ideal probes for exotic astrophysical processes, such as dark matter annihilations. At the same time, they can be used to measure two-nucleon correlations and density fluctuations in heavy ion collisions, which may shed light on the QCD phase diagram. Motivated by the importance of light antinuclei in cosmic ray studies, we developed a new coalescence model for light (anti)nuclei that includes both the size of the formation region, which is process dependent, and momentum correlations in a semi-classical picture. We have employed the model as an afterburner to the event generators Pythia 8 and QGSJET II, and find that the model agrees well with experimental data on antideuteron and antihelium-3 production in $e^{+} e^{-}$ , $pp$ , $p$ Be and $p$ Al collisions at various energies. In this paper, we review this model and update existing fits to experimental data based on new insights.
↳ hep-phnucl-thPoS(2021)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE

Electromagnetic form factors of the Ω− baryon in the spacelike and timelike regions

Kinematic Azimuthal Asymmetries and Lam-Tung Relation

Comprehensive test of the Brink-Axel hypothesis in the energy region of the pygmy dipole resonance

Formation of light (anti)nuclei

Affiliations

Electromagnetic form factors of the $Ω^{-}$ baryon in the spacelike and timelike regions