From atoms to nuclei, quarks and bejond...

Latest Results for Few-Body Systems

21 December 2024

• Production Cross-Section of $$\gamma $$ -Rays from (p,p $$^\prime \gamma $$ ) Reactions: Measurements and Theoretical Analysis

  Abstract

  This paper reviews our work on the measurements of absolute production cross sections of \(\gamma \) -rays from the (p,p \(^{\prime }\gamma \) ) reactions on \(^{12}\) C and \(^{16}\) O. The measurements cover a range of 8–16 MeV for the incident proton beam. The angular distributions of the \(\gamma \) -rays have been measured. A detailed phenomenological analysis within the framework of optical model formalism has been carried out to reproduce the experimental data. The existing global set of elastic, polarization and total reaction data for protons and neutrons have been used to generate the optical model potential. The nuclear structure effects have been included in the calculations by considering the roles of coupling of the low-lying states, the presence of resonances and nuclear deformations. The potentials so generated have been used to calculate the differential and total cross sections for both (p,p \(^\prime \) ) and (p,p \(^\prime \gamma \) ) reactions. The results of the analysis are in good agreement with the measured data for the observed \(\gamma \) -rays. However, discrepancies still exist in reproducing the finer details of the cross sections. The existing discrepancies between our phenomenological analysis and the experimental data demonstrate the rather complex roles of channel couplings, resonances in the compound nuclear system and target deformation. The significant contribution of nuclear structure effects in light mass nucleus like \(^{12}\) C and \(^{16}\) O, leads to an apparent loss of predictive power of the theoretical calculation for low-energy region (less than 10 MeV) of the projectile energy.

• Test of the Charge Symmetry Hypothesis of NN Interaction from the Coulomb-Free p–p Scattering Cross Section and Its Relation to Universality

  Abstract

  We examine the results on the determination of the Coulomb-free ¹ \(S_0\) proton–proton (p–p) scattering length by analyzing the cross section of the quasi-free p + d \(\rightarrow \) p + p + n reaction at center-of-mass energies below 1 MeV. This was achieved using a Bayesian data-fitting approach, yielding a p–p scattering length \(a_{pp} = -18.17^{+0.52}_{-0.58}|_{stat}\pm 0.01_{syst}\)  fm and effective range \(r_0 = 2.80\pm 0.05_{stat}\pm 0.001_{syst}\)  fm. We test the stability of the results against the upper energy cutoff and fitting data sets separately. A model based on the Eckart potential is introduced for an effective description in the universal window. In this model, the short-range interaction is considered as a whole, similar to how the s-wave phase-shift \(\delta \) functions in describing low-energy nucleon–nucleon scattering data. Based on our analysis, we confirm that the obtained parameters accurately represent the characteristics of the short-range physics and the influence of the up-down quark mass difference on the charge symmetry breaking is less significant as initially anticipated. Additionally, we suggest evaluating the charge symmetry breaking of the short-range interaction rather than solely focusing on the nuclear interaction.

• Isospin Symmetry of $$\omega $$ Meson at Finite Temperature in the Soft-Wall Model of Holographic QCD

  Abstract

  The coupling constants of \(\rho \) meson-nucleon and \(\omega \) meson-nucleon are connected through the isospin relation. Using the soft-wall model of holographic QCD, the current work aims to examine the violation (if any) of isospin symmetry of the \(\omega \) -meson as well as the temperature dependency of the \(\omega \) -meson- \(\Delta \) and \(\omega \) -meson-nucleon- \(\Delta \) baryon coupling constants. Applying the temperature-dependent profile functions of the vector and fermion fields to the expression of the coupling constants in the model yields the temperature dependence of the coupling constants. The minimum and magnetic type interactions between vector and fermion fields in 5-dimensional AdS space-time are included in the written interaction Lagrangian terms. The temperature dependence of the coupling constants \(g_{\omega N N}(T)\) , \(g_{\omega \Delta \Delta }(T)\) , and \(g_{\omega N \Delta }(T)\) has been investigated. Comparing \(g_{\omega NN}(T)\) with the coupling constant \(g_{\rho NN}(T)\) , it is found that the isospin symmetry of the \(\omega \) and \(\rho \) mesons is not violated at the finite temperature. It is also observed that the coupling constant of the \(\omega \) meson with baryons decreases as the temperature increases, and this coupling constant becomes zero near the confinement-deconfinement phase transition temperature.