Nuclear Theory·nucl-th

Wednesday·December 2, 2015

11 papers—4 primary·7 cross-listed

01
[Submitted on 1 Dec 2015]
Structure of the $Λ (1405)$ and the $K^{-} d \to π Σ n$ reaction
Shota Ohnishi🇯🇵 · Yoichi Ikeda🇯🇵 · Tetsuo Hyodo🇯🇵 · Wolfram Weise🇮🇹
The $Λ (1405)$ resonance production reaction is investigated within the framework of the coupled-channels Alt-Grassberger-Sandhas (AGS) equations. We perform full three-body calculations for the $K ˉ N N - π Y N$ amplitudes on the physical real energy axis and investigate how the signature of the $Λ (1405)$ appears in the cross sections of the $K^{-} d \to π Σ n$ reactions, also in view of the planned E31 experiment at J-PARC. Two types of meson-baryon interaction models are considered: an energy-dependent interaction based on chiral $S U (3)$ effective field theory, and an energy-independent version that has been used repeatedly in phenomenological approaches. These two models have different off-shell properties that imply correspondingly different behavior in the three-body system. We investigate how these features show up in differential cross sections of $K^{-} d \to π Σ n$ reactions. Characteristic patterns distinguishing between the two models are found in the invariant mass spectrum of the final $π Σ$ state. The $K^{-} d \to π Σ n$ reaction, with different ( $π^{\pm} Σ^{\mp}$ and $π^{0} Σ^{0}$ ) charge combinations in the final state, is thus demonstrated to be a useful tool for investigating the subthreshold behavior of the $K ˉ N$ interaction.
Comments:
14 pages, 14 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1512.00123 [pdf]
PRC(2016)·37 citations
02
[Submitted on 1 Dec 2015]
Two-gluon rapidity correlations of strong colour field in $pp$ , $p A$ and $AA$ collisions
Ye-Yin Zhao🇨🇳 · Ming-Mei Xu🇨🇳 · Heng-Ying Zhang🇨🇳 · Yuan-Fang Wu🇨🇳
Using the CGC formalism, we calculate the two-gluon rapidity correlations of strong colour fields in $pp$ , $p A$ and $AA$ collisions, respectively. If one trigger gluon is fixed at central rapidity, a ridge-like correlation pattern is obtained in symmetry $pp$ and $AA$ collisions, and a huge bump-like correlation pattern is presented in asymmetry $p A$ collisions. It is demonstrated that the ridge-like correlation patterns are caused by the stronger correlation with the gluon of colour source. The transverse momentum and incident energy dependence of the ridge-like correlation pattern is also systematically studied. The ridge is more likely observed at higher incident energy and lower transverse momentum of trigger gluon.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1512.00166 [pdf]
NPA(2016)·5 citations
03
[Submitted on 1 Dec 2015]
Dipole response in 208Pb within a self-consistent multiphonon approach
F. Knapp🇨🇿 · N. Lo Iudice🇮🇹 · P. Vesely🇨🇿 · F. Andreozzi🇮🇹 · G. De Gregorio🇮🇹 · A. Porrino🇮🇹
Background: The electric dipole strength detected around the particle threshold and commonly associated to the pygmy dipole resonance offers a unique information on neutron skin and symmetry energy, and is of astrophysical interest. The nature of such a resonance is still under debate. Purpose: We intend to describe the giant and pygmy resonances in 208 Pb by enhancing their fragmentation with respect to the random-phase approximation. Method: We adopt the equation of motion phonon method to perform a fully self-consistent calculation in a space spanned by one-phonon and two-phonon basis states using an optimized chiral two-body potential. A phenomenological density dependent term, derived from a contact three-body force, is added in order to get single-particle spectra more realistic than the ones obtained by using the chiral potential only. The calculation takes into full account the Pauli principle and is free of spurious center of mass admixtures. Results: We obtain a fair description of the giant resonance and obtain a dense low-lying spectrum in qualitative agreement with the experimental data. The transition densities as well as the phonon and particle-hole composi- tion of the most strongly excited states support the pygmy nature of the low-lying resonance. Finally, we obtain realistic values for the dipole polarizability and the neutron skin radius. Conclusions: The results emphasize the role of the two-phonon states in enhancing the fragmentation of the strength in the giant resonance region and at low energy, consistently with experiments. For a more detailed agreement with the data, the calculation suggests the inclusion of the three-phonon states as well as a fine tuning of the single-particle spectrum to be obtained by a refinement of the nuclear potential.
Comments:
13 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1512.00191 [pdf]
PRC(2015)·34 citations
04
[Submitted on 1 Dec 2015]
Role of $ω$ -meson exchange in scaling of the $γ p \to π^{0} p$ process from a Regge-type model with resonances
Kook-Jin Kong🇰🇷 · Tae Keun Choi🇰🇷 · Byung-Geel Yu🇰🇷
The scaling of photoproduction $γ p \to π^{0} p$ is investigated in the Reggeized model with $N^{*}$ and $Δ$ resonances included to describe resonance peaks up to photon energy $E_{γ}$ = 3 GeV. Given the $t$ -channel exchanges $ρ (770) + ω (780) + b_{1} (1235) + h_{1} (1170)$ Reggeized for the background contribution, the resonances of the Breit-Wigner form are introduced to agree with cross sections for total, differential and beam asymmetry in the low energy region. The scaled differential-cross sections $s^{7} d σ / d t$ are reproduced to agree with the recent JLab data, revealing the production mechanism of the big bump structure around $W \approx 2.2$ GeV by the deep-dip pattern of the $ω$ exchange that originates from the zeros of the trajectory $α_{ω} (t) = 0$ in the canonical phase, $\frac{1}{2} (- 1 + e^{- iπ α_{ω} (t)})$ .
Comments:
5 pages, 2 tables, 5 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1512.00238 [pdf]
PRC(2016)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE

Structure of the Λ(1405) and the K−d→πΣn reaction

Two-gluon rapidity correlations of strong colour field in pp, pA and AA collisions

Dipole response in 208Pb within a self-consistent multiphonon approach

Role of ω-meson exchange in scaling of the γp→π0p process from a Regge-type model with resonances

Affiliations

Structure of the $Λ (1405)$ and the $K^{-} d \to π Σ n$ reaction

Two-gluon rapidity correlations of strong colour field in $pp$ , $p A$ and $AA$ collisions

Role of $ω$ -meson exchange in scaling of the $γ p \to π^{0} p$ process from a Regge-type model with resonances