Production of Theta+ in gamma + D -> Lambda + Theta+ and gamma + D -> Sigma + Theta+ reactions

The gamma + D -> Lambda + Theta+ and gamma + D -> Sigma + Theta+ reactions can be used to determine the width of Theta+ almost model-independently. We calculate the differential cross sections of the gamma +D -> Lambda + Theta+, gamma + D -> Sigma + Theta+ and relevant background reactions in the photon energy range 1.2 < E_{\gamma} < 2.6 GeV. We determine the most favorable kinematic conditions and observables for the experimental studies of Theta+ in the considered processes. We argue that a comparison of the gamma + D -> Lambda + Theta+ and gamma + D -> Sigma + Theta+ cross sections should unambiguously determine isospin of Theta+.Comment: 22 pages, 9 figures. Final published versio

Dynamical coupled-channel model of kaon-hyperon interactions

The pi N --> KY and KY --> KY reactions are studied using a dynamical coupled-channel model of meson-baryon interactions at energies where the baryon resonances are strongly excited. The channels included are: pi N, K \Lambda, and K\Sigma. The resonances considered are: N^* [S_{11}(1650), P_{11}(1710), P_{13}(1720),D_{13}(1700)]; \Delta^* [S_{31}(1900), P_{31}(1910), P_{33}(1920)]; \Lambda ^* [S_{01}(1670), P_{01}(1810)] \Sigma^* [P_{11}(1660), D_{13}(1670)]; and K^*(892). The basic non-resonant \pi N --> KY and KY --> KY transition potentials are derived from effective Lagrangians using a unitary transformation method. The dynamical coupled-channel equations are simplified by parametrizing the pi N -->pi N amplitudes in terms of empirical pi N partial-wave amplitudes and a phenomenological off-shell function. Two models have been constructed. Model A is built by fixing all coupling constants and resonance parameters using SU(3) symmetry, the Particle Data Group values, and results from a constituent quark model. Model B is obtained by allowing most of the parameters to vary around the values of model A in fitting the data. Good fits to the available data for pi^- p to K^0 \Lambda, K^0 \Sigma^0 have been achieved. The investigated kinematics region in the center-of-mass frame goes from threshold to 2.5 GeV. The constructed models can be imbedded into associated dynamical coupled-channel studies of kaon photo- and electro-production reactions.Comment: 35 pages, 11 Figure

Measurement of the reaction \gamma p \TO K^ + \Lambda(1520) at photon energies up to 2.65 GeV

The reaction \gamma p \TO K^+\Lambda(1520) was measured in the energy range from threshold to 2.65 GeV with the SAPHIR detector at the electron stretcher facility ELSA in Bonn. The $\Lambda(1520)$ production cross section was analyzed in the decay modes $pK^-$, $n \bar{K}^0$, $\Sigma^{\pm}\pi^{\mp}$, and $\Lambda\pi^+\pi^-$ as a function of the photon energy and the squared four-momentum transfer $t$. While the cross sections for the inclusive reactions rise steadily with energy, the cross section of the process \gamma p \TO K^+\Lambda(1520) peaks at a photon energy of about 2.0 GeV, falls off exponentially with $t$, and shows a slope flattening with increasing photon energy. The angular distributions in the $t$-channel helicity system indicate neither a $K$ nor a $K^\star$ exchange dominance. The interpretation of the $\Lambda(1520)$ as a $\Sigma(1385)\pi$ molecule is not supported.Comment: 11 pages, 16 figures, 4 table

Measurement of gamma p --> K+ Lambda and gamma p --> K+ Sigma0 at photon energies up to 2.6 GeV

The reactions gamma p --> K+ Lambda and gamma p --> K+ Sigma0 were measured in the energy range from threshold up to a photon energy of 2.6 GeV. The data were taken with the SAPHIR detector at the electron stretcher facility, ELSA. Results on cross sections and hyperon polarizations are presented as a function of kaon production angle and photon energy. The total cross section for Lambda production rises steeply with energy close to threshold, whereas the Sigma0 cross section rises slowly to a maximum at about E_gamma = 1.45 GeV. Cross sections together with their angular decompositions into Legendre polynomials suggest contributions from resonance production for both reactions. In general, the induced polarization of Lambda has negative values in the kaon forward direction and positive values in the backward direction. The magnitude varies with energy. The polarization of Sigma0 follows a similar angular and energy dependence as that of Lambda, but with opposite sign.Comment: 21 pages, 25 figures, submitted to Eur. Phys. J.

Evidence for the positive-strangeness pentaquark Θ+\Theta^+ in photoproduction with the SAPHIR detector at ELSA

The positive--strangeness baryon resonance $\Theta^+$ is observed in photoproduction of the $\rm nK^+K^0_s$ final state with the SAPHIR detector at the Bonn ELectron Stretcher Accelerator ELSA. It is seen as a peak in the $\rm nK^+$ invariant mass distribution with a $4.8\sigma$ confidence level. We find a mass $\rm M_{\Theta^+} = 1540\pm 4\pm 2$ MeV and an upper limit of the width $\rm \Gamma_{\Theta^+} < 25$ MeV at 90% c.l. From the absence of a signal in the $\rm pK^+$ invariant mass distribution in $\rm\gamma p\to pK^+K^-$ at the expected strength we conclude that the $\Theta^+$ must be isoscalar.Comment: 9 pages, 4 figure

Study of nucleon resonances with electromagnetic interactions

Recent developments in using electromagnetic meson production reactions to study the structure of nucleon resonances are reviewed. Possible future works are discussed.Comment: 25 pages, 19 figure

A description of nesting behaviors, including factors impacting nest site selection, in black‐and‐white ruffed lemurs (Varecia variegata)

Nest site selection is at once fundamental to reproduction and a poorly understood component of many organisms’ reproductive investment. This study investigates the nesting behaviors of black-and-white ruffed lemurs, Varecia variegata, a litter-bearing primate from the southeastern rainforests of Madagascar. Using a combination of behavioral, geospatial, and demographic data, I test the hypotheses that environmental and social cues influence nest site selection and that these decisions ultimately impact maternal reproductive success. Gestating females built multiple large nests throughout their territories. Of these, females used only a fraction of the originally constructed nests, as well as several parking locations as infants aged. Nest construction was best predicted by environmental cues, including the size of the nesting tree and density of feeding trees within a 75 m radius of the nest, whereas nest use depended largely on the size and average distance to feeding trees within that same area. Microhabitat characteristics were unrelated to whether females built or used nests. Although unrelated to nest site selection, social cues, specifically the average distance to conspecifics’ nest and park sites, were related to maternal reproductive success; mothers whose litters were parked in closer proximity to others’ nests experienced higher infant survival than those whose nests were more isolated. This is likely because nesting proximity facilitated communal crèche use by neighboring females. Together, these results suggest a complex pattern of nesting behaviors that involves females strategically building nests in areas with high potential resource abundance, using nests in areas according to their realized productivity, and communally rearing infants within a network of nests distributed throughout the larger communal territory

Production of Lambda and Sigma^0 hyperons in proton-proton collisions

This paper reports results on simultaneous measurements of the reaction channels pp -> pK+\Lambda and pp -> pK+\Sigma^0 at excess energies of 204, 239, and 284 MeV (\Lambda) and 127, 162, and 207 MeV (\Sigma^0). Total and differential cross sections are given for both reactions. It is concluded from the measured total cross sections that the high energy limit of the cross section ratio is almost reached at an excess energy of only about 200 MeV. From the differential distributions observed in the overall CMS as well as in the Jackson and helicity frames, a significant contribution of interfering nucleon resonances to the \Lambda production mechanism is concluded while resonant \Sigma^0-production seems to be of lesser importance and takes place only through specific partial waves of the entrance channel. The data also indicate that kaon exchange plays a minor role in the case of \Lambda- but an important role for \Sigma^0-production. Thus the peculiar energy dependence of the \Lambda-to-\Sigma^0 cross section ratio appears in a new light as its explanation requires more than mere differences between the p\Lambda and the p\Sigma^0 final state interaction. The data provide a benchmark for theoretical models already available or yet to come.Comment: 18 pages, 10 figures; accepted by The European Physical Journal A (EPJ A

Three body systems with strangeness and exotic systems

We report on four $\Sigma$'s and three $\Lambda$'s, in the 1500 - 1800 MeV region, as two meson - one baryon S-wave $(1/2)^+$ resonances found by solving the Faddeev equations in the coupled channel approach, which can be associated to the existing $S$ = -1, $J^P= 1/2^+$ low lying baryon resonances. On the other hand we also report on a new, hidden strangeness $N^*$ state, mostly made of $K \bar{K} N$, with mass around 1920 MeV, which we think could be responsible for the peak seen in the $\gamma p \to K^+ \Lambda$ around this energy. Finally we address a very novel topic in which we show how few body systems of several $\rho$ mesons can be produced, with their spins aligned up to J=6, and how these states found theoretically can be associated to several known mesons with spins J=2,3,4,5,6.Comment: Talk at the 21st European Conference on Few Body Problems in Physics, Salamanca, Sep. 201

Electromagnetic Meson Production in the Nucleon Resonance Region

Recent experimental and theoretical advances in investigating electromagnetic meson production reactions in the nucleon resonance region are reviewed.Comment: 75 pages, 42 figure