Nuclear Theory·nucl-th

Monday·April 22, 2024

14 papers—4 primary·10 cross-listed

01
Study of the electromagnetic form factors of the nucleons in the timelike region
Qin-He Yang🇨🇳 · Di Guo🇨🇳 · Ming-Yan Li🇨🇳 · Ling-Yun Dai🇨🇳 · Johann Haidenbauer🇩🇪 · Ulf-G. Meißner🇩🇪
The electromagnetic form factors $G_{E}$ and $G_{M}$ of the proton and neutron in the timelike region are extracted in a study of the processes $e^{+} e^{-} \to p ˉ p$ and $e^{+} e^{-} \to n ˉ n$ . The reaction amplitude is evaluated within the distorted wave Born approximation, with the interaction of the antinucleon-nucleon ( $N ˉ N$ ) pair taken into account. The latter is constructed within $S U (3)$ chiral effective field theory up to the next-to-leading order. An excellent description of the $e^{+} e^{-} \to N ˉ N$ data in the energy region from the $N ˉ N$ threshold up to center-of-mass energies $E_{cm} = 2.2$ ~GeV is achieved. Results for the electromagnetic form factors $G_{E}, G_{M}$ , $G_{E} / G_{M}$ , and the subtracted effective form factors, $G_{osc}$ , are provided. These can be helpful for further studies of the properties of the nucleons.
nucl-thhep-phJHEP(2024)·8 citations
02
Nuclear charge radius predictions by kernel ridge regression with odd-even effects
Lu Tang · Zhen-Hua Zhang
The extended kernel ridge regression (EKRR) method with odd-even effects was adopted to improve the description of the nuclear charge radius using five commonly used nuclear models. These are: (i) the isospin dependent $A^{1/3}$ formula, (ii) relativistic continuum Hartree-Bogoliubov (RCHB) theory, (iii) Hartree-Fock-Bogoliubov (HFB) model HFB25, (iv) the Weizsäcker-Skyrme (WS) model WS $^{*}$ , and (v) HFB25 $^{*}$ model. In the last two models, the charge radii were calculated using a five-parameter formula with the nuclear shell corrections and deformations obtained from the WS and HFB25 models, respectively. For each model, the resultant root-mean-square deviation for the 1014 nuclei with proton number $Z \geq 8$ can be significantly reduced to 0.009-0.013~fm after considering the modification with the EKRR method. The best among them was the RCHB model, with a root-mean-square deviation of 0.0092~fm. The extrapolation abilities of the KRR and EKRR methods for the neutron-rich region were examined and it was found that after considering the odd-even effects, the extrapolation power was improved compared with that of the original KRR method. The strong odd-even staggering of nuclear charge radii of Ca and Cu isotopes and the abrupt kinks across the neutron $N = 126$ and 82 shell closures were also calculated and could be reproduced quite well by calculations using the EKRR method.
nucl-thnucl-exNucl.Sci.Tech.(2024)·28 citations
03
Nucleon microscopy in proton-nucleus scattering via analysis of bremsstrahlung emission: role of incoherent emission
Sergei P. Maydanyuk (1,2,4)🇨🇳 · Li-Ping Zou (2)🇨🇳 · Peng-Ming Zhang (3) ((1) Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai, China, (2) Wigner Research Centre for Physics, Budapest, Hungary, (3) School of Physics and Astronomy, Sun Yat-Sen University, Zhuhai, China, (4) Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kyiv, Ukraine)🇨🇳
We study electromagnetic form factors of protons in proton-nucleus scattering via analysing of experimental cross-sections of accompanying bremsstrahlung photons. A new bremsstrahlung model for proton-nucleus scattering is developed, where a main focus is given on incoherent bremsstrahlung that has not been considered previously. In analysis we choose experimental bremsstrahlung data of $p$ + $^{197}$ Au scattering at proton beam energy of 190 MeV obtained by TAPS collaboration. We find the following. (1) Inclusion of incoherent emission to calculations improves agreements with experimental data essentially, contribution of incoherent bremsstrahlung is essentially larger than coherent one. (2) Inclusion of form factors of the scattered proton improves agreement with experimental data in comparison with calculations with coherent and incoherent contributions without form factors. (3) Sensitivity of model in study of form factors of the scattered proton is high. This demonstrates a new opportunity to study internal structure of protons under influence of nuclear forces in nuclear scattering.
nucl-thhep-phPRC(2025)·0 citations
04
Hypernuclear constraints on the existence and lifetime of a deeply bound $H$ dibaryon
Avraham Gal🇮🇱
We study to what extent the unique observation of $ΛΛ$ hypernuclei by their weak decay into known $Λ$ hypernuclei, with lifetimes of order 10 $^{- 10}$ s, rules out the existence of a deeply bound doubly-strange ( $S$ = $-$ 2) $H$ dibaryon. Treating $_{ΛΛ}^{6} He$ (the Nagara emulsion event) in a realistic $Λ - Λ -^{4}$ He three-body model, we find that the $_{ΛΛ}^{6} He \to H +^{4} He$ strong-interaction lifetime increases beyond 10 $^{- 10}$ s for $m_{H} < m_{Λ} + m_{n}$ , about 176 MeV below the $ΛΛ$ threshold, so that such a deeply bound $H$ is not in conflict with hypernuclear data. Constrained by $Λ$ hypernuclear $Δ S$ =1 nonmesonic weak-interaction decay rates, we follow EFT methods to evaluate the $Δ S$ =2 $H \to nn$ weak-decay lifetime of $H$ in the mass range $2 m_{n} ≲ m_{H} < m_{Λ} + m_{n}$ . The resulting $H$ lifetime is of order 10 $^{5}$ s, many orders of magnitude shorter than required to qualify for a dark-matter candidate.
nucl-thhep-phnucl-exPLB(2024)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE

Study of the electromagnetic form factors of the nucleons in the timelike region

Nuclear charge radius predictions by kernel ridge regression with odd-even effects

Nucleon microscopy in proton-nucleus scattering via analysis of bremsstrahlung emission: role of incoherent emission

Hypernuclear constraints on the existence and lifetime of a deeply bound H dibaryon

Affiliations

Hypernuclear constraints on the existence and lifetime of a deeply bound $H$ dibaryon