The electro production of d* dibaryon

$d^*$ dibaryon study is a critical test of hadron interaction models. The electro production cross sections of $ed\to ed^*$ have been calculated based on the meson exchange current model and the cross section around 30 degree of 1 GeV electron in the laboratory frame is about 10 nb. The implication of this result for the $d^*$ dibaryon search has been discussed.Comment: 12 pages, 12 figures, Late

Comportamiento cleptoparásito en la Garcilla bueyera (Bubulcus ibis)

S'ofereixen algunes dades sobre el comportament cleptoparàsit de l'esplugabous en un abocador. La majoria dels robatoris van ser intraespecífics, només dos van anar dirigits a gavians foscos. L'èxit del robatori va ser del 35%. La presència d'aquest comportament en l'esplugabous probablement està relacionat en l'alta concentrcaió de preses i individus a l'abocador

Double neutral pion photoproduction at threshold

We consider the chiral expansion of the threshold amplitude for the reaction $\gamma p \to \pi^0 \pi^0 p$ to order ${\cal O}(M_\pi^2)$. We substantiate a claim that this photoproduction channel is significantly enhanced close to threshold due to pion loops. A precise measurement of the corresponding cross sections is called for which allows to test chiral perturbation theory.Comment: 8 pp, LaTe

Spin Information from Vector-Meson Decay in Photoproduction

For the photoproduction of vector mesons, all single and double spin observables involving vector meson two-body decays are defined consistently in the $\gamma N$ center of mass. These definitions yield a procedure for extracting physically meaningful single and double spin observables that are subject to known rules concerning their angle and energy evolution. As part of this analysis, we show that measuring the two-meson decay of a photoproduced $\rho$ or $\phi$ does not determine the vector meson's vector polarization, but only its tensor polarization. The vector meson decay into lepton pairs is also insensitive to the vector meson's vector polarization, unless one measures the spin of one of the leptons. Similar results are found for all double spin observables which involve observation of vector meson decay. To access the vector meson's vector polarization, one therefore needs to either measure the spin of the decay leptons, make an analysis of the background interference effects or relate the vector meson's vector polarization to other accessible spin observables.Comment: 22 pages, 3 figure

Double Pion Photoproduction on the Nucleon: Study of the Isospin Channels

A model for the gamma p ----> pion+ pion- p reaction developed earlier is extended to account for all isospin channels. The model includes N, Delta(1232), N^*(1440) and N^*(1520) as intermediate baryonic states and the rho-meson as an intermediate two pion resonance. Although many terms contribute to the cross section, some channels exhibit particular sensitivity to certain mechanisms of resonance excitation or decay and the reactions provide novel information on such mechanisms. In particular the gamma N ----> N^*(1520) ----> Delta(1232) pion process affects all the channels and is a key ingredient in the interpretation of the data. Comparison is made with all available data and the agreement is good in some channels. The remaining discrepancies in some other channels are discussed.Comment: 23 pages, 13 figures. TeX, Version 3.141 [PD VMS 3.4/CERN 1.0

Synthetic Mesh in Immediate Breast Reconstruction

The use of biological matrices in immediate implant-based breast reconstruction arose with the need to reinforce the lower pole of the breast and to cover the implant to reduce the risk of implant exposure. Synthetic mesh appears to be a lower cost alternative to biological matrices. This literature review aims to assess the usefulness of the use of synthetic meshes in breast reconstruction compared with the traditional techniques and whether outcomes and complications of synthetic meshes and biological matrices are comparable. The positioning of the implants and meshes, either submuscular or subcutaneous, has also been considered

The N*(1520) ---> Delta pi Amplitudes Extracted from the gamma p ---> pi+ pi- p Reaction and Comparison to Quark Models

The gamma p ---> pi+ pi- p reaction, in combination with data from the pi N ---> pi pi N reaction, allows one to obtain the s- and d-wave amplitudes for the N*(1520) decay into Delta pi with absolute sign with respect to the N*(1520) ---> N gamma helicity amplitudes. In addition one obtains the novel information on the q dependence of the amplitudes. This dependence fits exactly with the predictions of the non-relativistic constituent quark models. The absolute values provided by these models agree only qualitatively, and a discussion is done on the reasons for it and possible ways to improve.Comment: 12 pages, 1 figure, TeX, Version 3.141 [PD VMS 3.4/CERN 1.0

Theoretical study of the N N --> N N pi pi reaction

We have developed a model for the N N --> N N pi pi reaction and evaluated cross sections for the different charged channels. The low energy part of those channels where the pions can be in an isospin zero state is dominated by N* excitation, driven by an isoscalar source recently found experimentally, followed by the decay N* --> N (pi pi, T=0, s-wave). At higher energies, and in channels where the pions are not in T=0, Delta excitation mechanisms become relevant. A rough agreement with the experimental data is obtained in most channels. Repercussions of the present findings for the ABC effect and the p p --> p p pi0 reaction close to threshold are also suggested.Comment: 22 pages, 12 postscripts figures, revised: a more general N* N pi pi Lagrangian is considered, to be published in Nucl. Phys.

Study of polarization observables in double pion photoproduction on the proton

Using a model for two pion photoproduction on the proton previously tested in total cross sections and invariant mass distributions, we evaluate here polarization observables on which recent experiments are providing new information. We evaluate cross sections for spin 1/2 and 3/2, which are measured at Mainz and play an important role in tests of the GHD sum rule. We also evaluate the proton polarization asymmetry $\Sigma$ which is currently under investigation at GRAAL in Grenoble.Comment: 23 pages, 14 ps figure

A Model for the gamma p --> pi+ pi- p Reaction

[EN] We have studied the gammap--> pi+ pi- p reaction using a model which includes N, DELTA(1232), N*(1440) and N*(1520) intermediate baryonic states and the rho-meson as intermediate 2pi-resonance. The model reproduces fairly well experimental cross sections below E(gamma) = 800 MeV and invariant-mass distributions even at higher energies. One of the interesting findings of the study is that the gammaN --> N* (1520) --> DELTApi process is very important and interferes strongly with the dominant DELTA Kroll-Ruderman term to produce the experimental peak of the cross section. We show that the study of the reaction can provide information on some couplings, concretely the N*(1520) --> DELTApi. We also find that the pion energy distributions for different photon energies, which have not been measured so far, contain very valuable information on the dynamics of the reaction. Finally, the analogies and differences with respect to the piN --> 2piN reaction are also discussed.We are indebted to S.M. Singh who provided us with relevant information on the N*Ny coupling. Discussions with J.Bernabeu, F. Botella, P. González, S. Noguera, J. Peñarrocha and M.J. Vicente-Vacas are warmly acknowledged. This work has been partially supported by CICYT contract number AEN 90-049. One of us, J.A. Gómez Tejedor, wishes to acknowledge financial support from the Institució Valenciana d Estudis i InvestigacióGómez-Tejedor, J.; Oset, E. (1994). A Model for the gamma p --> pi+ pi- p Reaction. Nuclear Physics A. 571(4):667-693. https://doi.org/10.1016/0375-9474(94)90715-3S667693571