Current constraints on the EFT for the \Lambda N --> N N transition

The relation between the low energy constants appearing in the effective field theory description of the \Lambda N --> N N transition potential and the parameters of the one-meson-exchange model previously developed are obtained. We extract the relative importance of the different exchange mechanisms included in the meson picture by means of a comparison to the corresponding operational structures appearing in the effective approach. The ability of this procedure to obtain the weak baryon-baryon-meson couplings for a possible scalar exchange is also discussed.Comment: 10 pages, 6 figure

Fragmented condensation in Bose-Hubbard trimers with tunable tunnelling

We consider a Bose-Hubbard trimer, i.e. an ultracold Bose gas populating three quantum states. The latter can be either different sites of a triple-well potential or three internal states of the atoms. The bosons can tunnel between different states with variable tunnelling strength between two of them. This will allow us to study; i) different geometrical configurations, i.e. from a closed triangle to three aligned wells and ii) a triangular configuration with a $\pi$-phase, i.e. by setting one of the tunnellings negative. By solving the corresponding three-site Bose-Hubbard Hamiltonian we obtain the ground state of the system as a function of the trap topology. We characterise the different ground states by means of the coherence and entanglement properties. For small repulsive interactions, fragmented condensates are found for the $\pi$-phase case. These are found to be robust against small variations of the tunnelling in the small interaction regime. A low-energy effective many-body Hamiltonian restricted to the degenerate manifold provides a compelling description of the $\pi$-phase degeneration and explains the low-energy spectrum as excitations of discrete semifluxon states

Dynamical coupled-channel approach to hadronic and electromagnetic production of kaon-hyperon on the proton

A dynamical coupled-channel formalism for processes $\pi N \to KY$ and $\gamma N \to KY$ is presented which provides a comprehensive investigation of recent data on the $\gamma p \to K^+ \Lambda$ reaction. The non-resonant interactions within the subspace $KY\oplus\pi N$ are derived from effective Lagrangians, using a unitary transformation method. The calculations of photoproduction amplitudes are simplified by casting the coupled-channel equations into a form such that the empirical $\gamma N \to \pi N$ amplitudes are input and only the parameters associated with the $KY$ channel are determined by performing $\chi^2$-fits to all of the available data for $\pi^- p \to K^\circ\Lambda, K^\circ\Sigma^\circ$ and $\gamma p \to K^+\Lambda$. Good agreement between our models and those data are obtained. In the fits to $\pi N \to KY$ channels, most of the parameters are constrained within $\pm 20$ of the values given by the Particle Data Group and/or quark model predictions, while for $\gamma p \to K^+ \Lambda$ parameters, ranges compatible with broken $SU(6)\otimes O(3)$ symmetry are imposed. The main reaction mechanisms in $K^+ \Lambda$ photoproduction are singled out and issues related to newly suggested resonances $S_{11}$, $P_{13}$, and $D_{13}$ are studied. Results illustrating the importance of using a coupled-channel treatment are reported. Meson cloud effects on the $\gamma N \to N^*$ transitions are also discussed.Comment: Accepted Physical Review

Electroexcitation of the Roper resonance from CLAS data

The helicity amplitudes of the electroexcitation of the Roper resonance on proton are extracted at 1.7 < Q2 < 4.2 GeV2 from recent high precision JLab-CLAS cross sections data and longitudinally polarized beam asymmetry for pi+ electroproduction on protons. The analysis is made using two approaches, dispersion relations and unitary isobar model, which give consistent results. It is found that the transverse helicity amplitude for the gamma* p --> P11(1440) transition, which is large and negative at Q2=0, becomes large and positive at Q2 ~ 2 GeV2, and then drops slowly with Q2. Longitudinal helicity amplitude, that was previously found from CLAS data as large and positive at Q2=0.4,0.65 GeV2, drops with Q2. These results rule out the presentation of P11(1440) as a 3qG hybrid state, and provide strong evidence in favor of this resonance as a first radial excitation of the 3q ground state.Comment: 3 pages, 2 figures, Talk on the Workshop on "The Physics of Excited Nucleons", Bonn, Germany, October 200

Microscopic NN→NN∗(1440)NN\to NN^{\ast}(1440) transition potential: Determination of πNN∗(1440)\pi NN^{\ast}(1440) and σNN∗(1440)\sigma NN^{\ast}(1440) coupling constants

A $NN\to NN^{\ast}(1440)$ transition potential, based on an effective quark-quark interaction and a constituent quark cluster model for baryons, is derived in the Born-Oppenheimer approach. The potential shows significant differences with respect to those obtained by a direct scaling of the nucleon-nucleon interaction. From its asymptotic behavior we extract the values of $\pi NN^{\ast}(1440)$ and $\sigma NN^{\ast}(1440)$ coupling constants in a particular coupling schemeComment: 15 eps figures, Accepted for publication in Phys. Rev.

Matter-wave recombiners fro trapped Bose-Einstein condensates

Interferometry with trapped atomic Bose-Einstein condensates (BECs) requires the development of techniques to recombine the two paths of the interferometer and map the accumulated phase difference to a measurable atom number difference. We have implemented and compared two recombining procedures in a double-well-based BEC interferometer. The first procedure utilizes the bosonic Josephson effect and controlled tunneling of atoms through the potential barrier, similar to laser light in an optical fiber coupler. The second one relies on the interference of the reflected and transmitted parts of the BEC wave function when impinging on the potential barrier, analogous to light impinging on a half-silvered mirror. Both schemes were implemented successfully, yielding an interferometric contrast of similar to 20% and 42% respectively. Building efficient matter-wave recombiners represents an important step towards the coherent manipulation of external quantum superposition states of BECs

Coupled-channels study of the π−p→ηn\pi^{-}p \to \eta n process

The reaction $\pi^{-}p \to \eta n$ is investigated within a dynamical coupled-channels model of meson production reactions in the nucleon resonance region. The meson baryon channels included are $\pi N$, $\eta N$, $\pi \Delta$, $\sigma N$, and $\rho N$. The non-resonant meson-baryon interactions of the model are derived from a set of Lagrangians by using a unitary transformation method. One or two excited nucleon states in each of $S$, $P$, $D$, and $F$ partial waves are included to generate the resonant amplitudes. Data of $\pi^{-}p \to \eta n$ reaction from threshold up to a total center-of-mass energy of about 2 GeV are satisfactorily reproduced and the roles played by the following nine nucleon resonances are investigated: $S_{11}(1535)$, $S_{11}(1650)$, $P_{11}(1440)$, $P_{11}(1710)$, $P_{13}(1720)$, $D_{13}(1520)$, $D_{13}(1700)$, $D_{15}(1675)$, and $F_{15}(1680)$. The reaction mechanism as well as the predicted $\eta N$ scattering length are discussed.Comment: 22 pages, 8 figure