Nuclear Theory·nucl-th

Thursday·February 11, 2016

9 papers—6 primary·3 cross-listed

07
[Submitted on 10 Feb 2016] (cross-list from hep-ph)
Improved empirical parametrizations of the $γ^{*} N \to N (1535)$ transition amplitudes and the Siegert's theorem
G. Ramalho🇧🇷
Some empirical parametrizations of the $γ^{*} N \to N (1535)$ transition amplitudes violates the Siegert's theorem, that relates the longitudinal and the transverse amplitudes, in the pseudo-threshold limit (nucleon and resonance at rest). In the case of the electromagnetic transition from the nucleon (mass $M$ ) to the resonance $N (1525)$ (mass $M_{R}$ ), the Siegert's theorem is sometimes expressed by the relation $∣ q ∣ A_{1/2} = λ S_{1/2}$ in the pseudo-threshold limit, when the photon momentum $∣ q ∣$ vanishes, and $λ = 2 (M_{R} - M)$ . In this article, we argue that the Siegert's theorem should be expressed by the relation $A_{1/2} = λ \frac{S _{1/2}}{∣ q ∣}$ , in the limit $∣ q ∣ \to 0$ . This result is a consequence of the relation $S_{1/2} \propto ∣ q ∣$ , when $∣ q ∣ \to 0$ , as suggested by the analysis of the transition form factors and by the orthogonality between the nucleon and $N (1535)$ states. We propose then new empirical parametrizations for the $γ^{*} N \to N (1535)$ helicity amplitudes, that are consistent with the data and the Siegert's theorem. The proposed parametrization follow closely the MAID2007 parametrization, except for a small deviation in the amplitudes $A_{1/2}$ and $S_{1/2}$ when $Q^{2} < 1.5$ GeV $^{2}$ .
Comments:
To appear in the Phys.Lett.B. 7 pages, 4 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1602.03444 [pdf]
PLB(2016)·21 citations
08
[Submitted on 10 Feb 2016] (cross-list from hep-ph)
Progress in the calculation of nucleon transition form factors
Gernot Eichmann🇩🇪
We give a brief account of the Dyson-Schwinger and Faddeev-equation approach and its application to nucleon resonances and their transition form factors. We compare the three-body with the quark-diquark approach and present a quark-diquark calculation for the low-lying nucleon resonances including scalar, axialvector, pseudoscalar and vector diquarks. We also discuss the timelike structure of transition form factors and highlight the advantages of form factors over helicity amplitudes.
Comments:
8 pages, 8 figures, 2 tables. Proceedings of the ECT* Workshop "Nucleon Resonances: From Photoproduction to High Photon Virtualities", October 12-16, 2015, Trento, Italy
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1602.03462 [pdf]
Few Body Syst.(2016)·14 citations
09
[Submitted on 10 Feb 2016] (cross-list from hep-lat)
Fate of the Tetraquark Candidate Zc(3900) from Lattice QCD
Yoichi Ikeda (Nishina Ctr., RIKEN)🇯🇵 · Sinya Aoki (Kyoto U., YITP and Tsukuba U., CCS)🇯🇵 · Takumi Doi (Nishina Ctr., RIKEN)🇯🇵 · Shinya Gongyo (Kyoto U., YITP)🇯🇵 · Tetsuo Hatsuda (Nishina Ctr., RIKEN and Tokyo U., IPMU)🇯🇵 · Takashi Inoue (Nihon U.)🇯🇵 · Takumi Iritani (Stony Brook U.)🇺🇸 · Noriyoshi Ishii (Osaka U., RCNP)🇯🇵 · Keiko Murano (Osaka U., RCNP)🇯🇵 · Kenji Sasaki (Tsukuba U., CCS) (HAL QCD Collaboration)🇯🇵
The possible exotic meson $Z_{c} (3900)$ , found in $e^{+} e^{-}$ reactions, is studied by the method of coupled-channel scattering in lattice QCD. The interaction among $π J / ψ$ , $ρ η_{c}$ and $D ˉ D^{*}$ channels is derived from (2+1)-flavor QCD simulations at $m_{π} = 410$ - $700$ MeV. The interaction is dominated by the off-diagonal $π J / ψ$ - $D ˉ D^{*}$ and $ρ η_{c}$ - $D ˉ D^{*}$ couplings, which indicates that the $Z_{c} (3900)$ is not a usual resonance but a threshold cusp. Semi-phenomenological analyses with the coupled-channel interaction are presented to confirm this conclusion.
Comments:
5 pages, 6 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1602.03465 [pdf]
PRL(2016)·131 citations

Affiliations

first authorsco-authorsvia INSPIRE

Improved empirical parametrizations of the γ∗N→N(1535) transition amplitudes and the Siegert's theorem

Progress in the calculation of nucleon transition form factors

Fate of the Tetraquark Candidate Zc(3900) from Lattice QCD

Affiliations

Improved empirical parametrizations of the $γ^{*} N \to N (1535)$ transition amplitudes and the Siegert's theorem