Nuclear Theory·nucl-th

Thursday·July 16, 2015

7 papers—1 primary·6 cross-listed

01
Proton-neutron pairing in N=Z nuclei: quartetting versus pair condensation
N. Sandulescu · D. Negrea · D. Gambacurta
The isoscalar proton-neutron pairing and isovector pairing, including both isovector proton-neutron pairing and like-particle pairing, are treated in a formalism which conserves exactly the particle number and the isospin. The formalism is designed for self-conjugate (N=Z) systems of nucleons moving in axially deformed mean fields and interacting through the most general isovector and isoscalar pairing interactions. The ground state of these systems is described by a superposition of two types of condensates, i.e., condensates of isovector quartets, built by two isovector pairs coupled to the total isospin T=0, and condensates of isoscalar proton-neutron pairs. The comparison with the exact solutions of realistic isovector-isoscalar pairing Hamiltonians shows that this ansatz for the ground state is able to describe with high precision the pairing correlation energies. It is also shown that, at variance with the majority of Hartree-Fock-Bogoliubov calculations, in the present formalism the isovector and isoscalar pairing correlations coexist for any pairing interactions. The competition between the isovector and isoscalar proton-neutron pairing correlations is studied for N=Z nuclei with the valence nucleons moving in the $s d$ and $p f$ shells and in the major shell above $^{100}$ Sn. We find that in these nuclei the isovector pairing prevail over the isoscalar pairing, especially for heavier nuclei. However, the isoscalar proton-neutron correlations are significant in all nuclei and they always coexist with the isovector pairing correlations.
nucl-thPLB(2015)·36 citations
02
Splitting of ISGMR strength in the light-mass nucleus $^{24}$ Mg due to ground-state deformation
Y. K. Gupta🇺🇸 · U. Garg🇺🇸 · J. T. Matta🇺🇸 · D. Patel🇺🇸 · T. Peach🇺🇸 · J. Hoffman🇺🇸 · K. Yoshida🇯🇵 · M. Itoh🇯🇵 · M. Fujiwara🇯🇵 · K. Hara🇯🇵 · H. Hashimoto🇯🇵 · K. Nakanishi🇯🇵 and 10 other authors
The isoscalar giant monopole resonance (ISGMR) strength distribution in $^{24}$ Mg has been determined from background-free inelastic scattering of 386-MeV $α$ particles at extreme forward angles, including 0 $^{\circ}$ . The ISGMR strength distribution has been observed for the first time to have a two-peak structure in a light-mass nucleus. This splitting of ISGMR strength is explained well by microscopic theory in terms of the prolate deformation of the ground state of $^{24}$ Mg.
↳ nucl-exnucl-thPLB(2015)·44 citations
03
Towards exotic hidden-charm pentaquarks in QCD
Hua-Xing Chen🇨🇳 · Wei Chen🇨🇦 · Xiang Liu🇨🇳 · T. G. Steele🇨🇦 · Shi-Lin Zhu🇨🇳
Inspired by $P_{c} (4380)$ and $P_{c} (4450)$ recently observed by LHCb, a QCD sum rule investigation is performed, by which they can be identified as exotic hidden-charm pentaquarks composed of an anti-charmed meson and a charmed baryon. Our results suggest that $P_{c} (4380)$ and $P_{c} (4450)$ have quantum numbers $J^{P} = 3/ 2^{-}$ and $5/ 2^{+}$ , respectively. Furthermore, two extra hidden-charm pentaqurks with configurations $D ˉ Σ_{c}^{*}$ and $D ˉ^{*} Σ_{c}^{*}$ are predicted, which have spin-parity quantum numbers $J^{P} = 3/ 2^{-}$ and $J^{P} = 5/ 2^{+}$ , respectively. As an important extension, the mass predictions of hidden-bottom pentaquarks are also given. Searches for these partners of $P_{c} (4380)$ and $P_{c} (4450)$ are especially accessible at future experiments like LHCb and BelleII.
↳ hep-phhep-exhep-latnucl-thPRL(2015)·297 citations
04
Small-angle scattering and quasiclassical approximation beyond leading order
P. A. Krachkov · R. N. Lee · A.I. Milstein
In the present paper we examine the accuracy of the quasiclassical approach on the example of small-angle electron elastic scattering. Using the quasiclassical approach, we derive the differential cross section and the Sherman function for arbitrary localized potential at high energy. These results are exact in the atomic charge number and correspond to the leading and the next-to-leading high-energy small-angle asymptotics for the scattering amplitude. Using the small-angle expansion of the exact amplitude of electron elastic scattering in the Coulomb field, we derive the cross section and the Sherman function with a relative accuracy $θ^{2}$ and $θ^{1}$ , respectively ( $θ$ is the scattering angle). We show that the correction of relative order $θ^{2}$ to the cross section, as well as that of relative order $θ^{1}$ to the Sherman function, originates not only from the contribution of large angular momenta $l ≫ 1$ , but also from that of $l \sim 1$ . This means that, in general, it is not possible to go beyond the accuracy of the next-to-leading quasiclassical approximation without taking into account the non-quasiclassical terms.
↳ physics.atom-phnucl-thPLB(2015)·3 citations
05
Pion String evolving in a thermal bath
Fan Lu🇨🇳 · Qichang Chen🇨🇳 · Hong Mao🇨🇳
By using the symmetry improved CJT effective formalism, we study a pion string of the $O (4)$ linear sigma model at finite temperature in chiral limit. In terms of the Kibble-Zurek mechanism we reconsider the production and evolution of the pion string in a thermal bath. Finally, we estimate the pion string density and its possible signal during the chiral phase transition.
↳ hep-phnucl-thPRD(2015)·5 citations
06
Shear Viscosities of Photons in Strongly Coupled Plasmas
Di-Lun Yang🇬🇷 · Berndt Müller🇺🇸
We investigate the shear viscosity of thermalized photons in the quark gluon plasma (QGP) at weak coupling and $N = 4$ super Yang-Mills plasma (SYMP) at both strong and weak couplings. We find that the shear viscosity due to the photon-parton scattering up to the leading order of electromagnetic coupling is suppressed when the coupling of the QGP/SYMP is increased, which stems from the blue-shift of the thermal-photon spectrum at strong coupling. In addition, the shear viscosity rapidly increases near the deconfinement transition in a phenomenological model analogous to the QGP.
↳ hep-thhep-phnucl-thPLB(2016)·16 citations
07
Temperature-dependent cross sections for charmonium dissociation in collisions with kaons and eta mesons in hadronic matter
Shi-Tao Ji🇨🇳 · Zhen-Yu Shen🇨🇳 · Xiao-Ming Xu🇨🇳
We study kaon-charmonium and eta-charmonium dissociation reactions. The K-charmonium dissociation and the eta-charmonium dissociation include 27 reactions. Cross sections for the reactions are calculated in the Born approximation, in the quark-interchange mechanism and with a temperature-dependent quark potential. The temperature dependence of peak cross sections of endothermic reactions is linked to the temperature dependence of quark-antiquark relative-motion wave functions, meson masses and the quark potential. Although the eta meson and kaon have similar masses, the energy and temperature dependence of the eta-charmonium dissociation cross sections are quite different from those of the K-charmonium dissociation cross sections. Using the eta-charmonium and pion-charmonium dissociation cross sections, we calculate the ratio of the corresponding dissociation rates in hadronic matter and we find that such rates are comparable at low J/psi momenta.
↳ hep-phnucl-thJ.Phys.G(2015)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE

Proton-neutron pairing in N=Z nuclei: quartetting versus pair condensation

Splitting of ISGMR strength in the light-mass nucleus 24Mg due to ground-state deformation

Towards exotic hidden-charm pentaquarks in QCD

Small-angle scattering and quasiclassical approximation beyond leading order

Pion String evolving in a thermal bath

Shear Viscosities of Photons in Strongly Coupled Plasmas

Temperature-dependent cross sections for charmonium dissociation in collisions with kaons and eta mesons in hadronic matter

Affiliations

Splitting of ISGMR strength in the light-mass nucleus $^{24}$ Mg due to ground-state deformation