Re-examining the X(4630)X(4630) resonance in the reaction e+e−→Λc+Λˉc−e^+e^-\rightarrow \Lambda^+_c\bar\Lambda^-_c

The reaction $e^+e^-\rightarrow \Lambda^+_c\bar\Lambda^-_c$ is investigated at energies close to the threshold with emphasis on the role played by the $X(4630)$ resonance. The interaction in the final $\Lambda^+_c \bar\Lambda^-_c$ system, constructed within chiral effective field theory and supplemented by a pole diagram that represents a bare $X(4630)$ resonance, is taken into account rigorously. The pole parameters of the $X(4630)$ are extracted and found to be compatible with the ones of the $X(4660)$ resonance that have been established in the reaction $e^+e^- \to \pi^+\pi^-\psi(2S)$. The actual result for the $X(4630)$ is $M = (4652.5\pm 3.4)$ MeV and $\Gamma = (62.6\pm 5.6)$ MeV. Predictions for the $\Lambda^+_c$ electromagnetic form factors in the timelike region are presented.Comment: 11 pages, 3 figure

J/ψ→γη′π+π−J/\psi \to \gamma\eta'\pi^+\pi^- and the structure observed around the pˉp\bar pp threshold

We analyze the origin of the structure observed in the reaction $J/\psi \to \gamma \eta'\pi^+\pi^-$ for $\eta'\pi^+\pi^-$ invariant masses close to the antiproton-proton ($\bar pp$) threshold, commonly associated with the $X(1835)$ resonance. Specifically, we explore the effect of a possible contribution from the two-step process $J/\psi \to \gamma \bar NN \to \gamma \eta'\pi^+\pi^-$. The calculation is performed in distorted-wave Born approximation which allows an appropriate inclusion of the $\bar NN$ interaction in the transition amplitude. The $\bar NN$ amplitude itself is generated from a corresponding potential recently derived within chiral effective field theory. We are able to reproduce the measured spectra for the reactions $J/\psi \to \gamma \bar pp$ and $J/\psi \to \gamma \eta'\pi^+\pi^-$ for invariant masses around the $\bar pp$ threshold. The structure seen in the $\eta'\pi^+\pi^-$ spectrum emerges as a threshold effect due to the opening of the $\bar pp$ channel.Comment: 9 pages, 5 figure

Antinucleon-nucleon interaction in chiral effective field theory

Results of an exploratory study of the antinucleon-nucleon interaction within chiral effective field theory are reported. The antinucleon-nucleon potential is derived up to next-to-next-to-leading order, based on a modified Weinberg power counting, in close analogy to pertinent studies of the nucleon-nucleon interaction. The low-energy constants associated with the arising contact interactions are fixed by a fit to phase shifts and inelasticities provided by a recently published phase-shift analysis of antiproton-proton scattering data. The overall quality of the achieved description of the antinucleon-nucleon amplitudes is comparable to the one found in case of the nucleon-nucleon interaction at the same order. For most S-waves and several P-waves good agreement with the antinucleon-nucleon phase shifts and inelasticities is obtained up to laboratory energies of around 200 MeV.Comment: 24 pp, uses JHEP styl

Antinucleon-nucleon interaction in chiral effective field theory

Results of an exploratory study of the antinucleon-nucleon interaction within chiral effective field theory are reported. The antinucleon-nucleon potential is derived up to next-to-next-to-leading order, based on a modified Weinberg power counting, in close analogy to pertinent studies of the nucleon-nucleon interaction. The low-energy constants associated with the arising contact interactions are fixed by a fit to phase shifts and inelasticities provided by a recently published phase-shift analysis of antiproton-proton scattering data. The overall quality of the achieved description of the antinucleon-nucleon amplitudes is comparable to the one found in case of the nucleon-nucleon interaction at the same order. For most S-waves and several P-waves good agreement with the antinucleon-nucleon phase shifts and inelasticities is obtained up to laboratory energies of around 200 MeV.Comment: 24 pp, uses JHEP styl

ΛΛˉ\Lambda\bar\Lambda final-state interaction in the reactions e+e−→ϕΛΛˉe^+e^-\to \phi\Lambda \bar \Lambda and e+e−→ηΛΛˉe^+e^- \to \eta\Lambda \bar \Lambda

Near-threshold $\Lambda\bar\Lambda$ mass spectra for the reactions $e^+e^- \to \eta\Lambda\bar\Lambda$ and $e^+e^- \to \phi\Lambda\bar\Lambda$ are investigated with an emphasis on the role played by the interaction in the $\Lambda\bar\Lambda$ system. A variety of $\Lambda\bar\Lambda$ potential models is employed that have been established in the analysis of data on $p\bar p\to \Lambda\bar\Lambda$ in the past. It is shown that the near-threshold enhancement observed for the two $e^+e^-$ reactions can be reproduced by considering the $\Lambda\bar\Lambda$ final-state interaction in the partial waves suggested by the helicity-angle analysis of the experiments. For $e^+e^- \to \eta\Lambda\bar\Lambda$ the same $\Lambda\bar\Lambda$ $S$-wave interaction as in $e^+e^- \to \Lambda\bar\Lambda$ is relevant and with it a consistent description of the pertinent measurements can be achieved. It is pointed out that a nonzero threshold cross section as observed for the latter reaction is not supported by the new $\eta\Lambda\bar\Lambda$ data.Comment: 8 pages, 5, figure

Predictions for charmed nuclei based on YcNY_c N forces inferred from lattice QCD simulations

Charmed nuclei are investigated utilizing $\Lambda_c N$ and $\Sigma_c N$ interactions that have been extrapolated from lattice QCD simulations at unphysical masses of $m_\pi = 410$--$570$ MeV to the physical point using chiral effective field theory as guideline. Calculations of the energies of $\Lambda_c$ single-particle bound states for various charmed nuclei from $^{\ 5}_{\Lambda_c}$Li to$^{209}_{\Lambda_c}$Bi are performed using a perturbative many-body approach. This approach allows one to determine the finite nuclei$\Lambda_c$self-energy from which the energies of the different bound states can be obtained. Though the$\Lambda_c N$interaction inferred from the lattice results is only moderately attractive, it supports the existence of charmed nuclei. Already the lightest nucleus considered is found to be bound. The spin-orbit splitting of the p- and d-wave states turns out to be small, as in the case of single$\Lambda$hypernuclei. Additional calculations based on the Faddeev-Yakubovsky equations suggest that also$A=4$systems involving a$\Lambda_c$baryon are likely to be bound, but exclude a bound$^{\, 3}_{\Lambda_c}$He state.Comment: 13 pages, 5 figure

Jacobi no-core shell model for pp-shell hypernuclei

We extend the recently developed Jacobi no-core shell model to hypernuclei. Based on the coefficients of fractional parentage for ordinary nuclei, we define a basis where the hyperon is the spectator particle. We then formulate transition coefficients to states that single out a hyperon-nucleon pair which allow us to implement a hypernuclear many-baryon Hamiltonian for $p$-shell hypernuclei. As a first application, we use the basis states and the transition coefficients to calculate the ground states of $^{4}_{\Lambda}$He, $^{4}_{\Lambda}$H, $^{5}_{\Lambda}$He, $^{6}_{\Lambda}$He, $^{6}_{\Lambda}$Li, and $^{7}_{\Lambda}$Li and, additionally, the first excited states of $^{4}_{\Lambda}$He, $^{4}_{\Lambda}$H, and $^{7}_{\Lambda}$Li. In order to obtain converged results, we employ the similarity renormalization group (SRG) to soften the nucleon-nucleon and hyperon-nucleon interactions. Although the dependence on this evolution of the Hamiltonian is significant, we show that a strong correlation of the results can be used to identify preferred SRG parameters. This allows for meaningful predictions of hypernuclear binding and excitation energies. The transition coefficients will be made publicly available as HDF5 data files.Comment: 20 pages, 1 table, 12 figure

S-shell ΛΛ\Lambda\Lambda hypernuclei based on chiral interactions

We generalize the Jacobi no-core shell model (J-NCSM) to study double-strangeness hypernuclei. All particle conversions in the strangeness $S=-1,-2$ sectors are explicitly taken into account. In two-body space, such transitions may lead to the coupling between states of identical particles and of non-identical ones. Therefore, a careful consideration is required when determining the combinatorial factors that connect the many-body potential matrix elements and the free-space two-body potentials. Using second quantization, we systematically derive the combinatorial factors in question for $S=0,-1,-2$ sectors. As a first application, we use the J-NCSM to investigate $\Lambda \Lambda$ s-shell hypernuclei based on hyperon-hyperon (YY) potentials derived within chiral effective field theory at leading order (LO) and up to next-to-leading order (NLO). We find that the LO potential overbinds $^{\text{ }\text{ }\text{ } \text{}6}_{\Lambda \Lambda}\text{He}$ while the prediction of the NLO interaction is close to experiment. Both interactions also yield a bound state for $^{\text{ }\text{ }\text{ } \text{}5}_{\Lambda \Lambda}\text{He}$. The $^{\text{}\text{ }\text{ }\text{}4}_{\Lambda \Lambda}\text{H}$ system is predicted to be unbound.Comment: 23 pages, 3 figure

Hyperon-nucleon interaction in chiral effective field theory at next-to-next-to-leading order

A hyperon-nucleon potential for the strangeness $S=-1$ sector ($\Lambda N$, $\Sigma N$) up to third order in the chiral expansion is presented. SU(3) flavor symmetry is imposed for constructing the interaction, however, the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons and in the leading-order contact terms is taken into account. A novel regularization scheme is employed which has already been successfully used in studies of the nucleon-nucleon interaction within chiral effective field theory up to high orders. An excellent description of the low-energy $\Lambda p$, $\Sigma^- p$ and $\Sigma^+ p$ scattering data is achieved. New data from J-PARC on angular distributions for the $\Sigma N$ channels are analyzed. Results for the hypertriton and $A=4$ hyper-nuclear separation energies are presented. An uncertainty estimate for the chiral expansion is performed for selected hyperon-nucleon observables.Comment: 30 pages, 13 figure

New insights into the oscillation of the nucleon electromagnetic form factors

The electromagnetic form factors of the proton and the neutron in the timelike region are investigated. The electron-positron annihilation into antinucleon-nucleon ($\bar NN$) pairs is treated in distorted wave Born approximation, including the final-state interaction in the $\bar NN$ system. The latter is obtained by a Lippmann-Schwinger equation for $\bar{N}N$ potentials derived within SU(3) chiral effective field theory. By fitting to the phase shifts and (differential) cross section data, a high quality description is achieved. With these amplitudes, the oscillations of the electromagnetic form factors of the proton and the neutron are studied. It is found that each of them can be described by two fractional oscillators. One is characterized as \lq overdamped' and dominates near the threshold, while the other is \lq underdamped' and plays an important role in the high-energy region. These two oscillators are essential to understand the distributions of polarized electric charges induced by hard photons for the nucleons.Comment: 5 pages, 3 figures, add some discussion