Search results for "Strangeness"
showing 10 items of 118 documents
Odd-parity light baryon resonances
2011
We use a consistent SU(6) extension of the meson-baryon chiral Lagrangian within a coupled channel unitary approach in order to calculate the T-matrix for meson-baryon scattering in s-wave. The building blocks of the scheme are the pion and nucleon octets, the rho nonet and the Delta decuplet. We identify poles in this unitary T-matrix and interpret them as resonances. We study here the non exotic sectors with strangeness S=0,-1,-2,-3 and spin J=1/2, 3/2 and 5/2. Many of the poles generated can be associated with known N, Delta, Sigma, Lambda and Xi resonances with negative parity. We show that most of the low-lying three and four star odd parity baryon resonances with spin 1/2 and 3/2 can …
Dynamical generation of hyperon resonances
2003
In this talk we report on how, using a chiral unitary approach for the meson--baryon interactions, two octets of $J^{\pi}=1/2^-$ baryon states and a singlet are generated dynamically, resulting in the case of strangeness $S=-1$ in two poles of the scattering matrix close to the nominal $\Lambda(1405)$ resonance. We suggest experiments which could show evidence for the existence of these states.
Interaction effects in ${\bm K^+}$ photoproduction on the deuteron
2004
Kaon photoproduction on the deuteron is studied with respect to a specific two-body contribution, namely a pion mediated production process, besides other final state interaction contributions from kaon-nucleon and hyperon-nucleon scattering. In this process, a pion is first photoproduced on one nucleon and then interacts with the spectator nucleon in a strangeness exchange reaction leading to a kaon and a hyperon. A sizeable effect from this pion mediated contribution is found, considerably larger than the previously studied hyperon-nucleon rescattering, whereas kaon-nucleon rescattering is much less important. Besides total and semi-inclusive differential cross sections, tensor target asy…
Nucleon strangeness and unitarity
1996
The strange-quark vector current form factors of the nucleon are analyzed within the framework of dispersion relations. Particular attention is paid to contributions made by $K\bar{K}$ intermediate states to the form factor spectral functions. It is shown that, when the $K\bar{K}\to N\bar{N}$ amplitude is evaluated in the Born approximation, the $K\bar{K}$ contributions are identical to those arising from a one-loop calculation and entail a serious violation of unitarity. The mean square strangeness radius and magnetic moment are evaluated by imposing unitarity bounds on the kaon-nucleon partial wave amplitudes. The impact of including the kaon's form factor in the dispersion integrals is a…
DYNAMICALLY GENERATED RESONANCES IN THE CHIRAL UNITARY APPROACH TO MESON BARYON INTERACTION
2004
In this talk we report on the use of a chiral unitary approach for the interaction of the octets of meson and baryon and the octet of mesons with the decuplet of baryons. Two octets of $J^{\pi}=1/2^-$ baryon states and a singlet are generated dynamically in the first case, resulting in the case of strangeness $S=-1$ in two poles of the scattering matrix close to the nominal $\Lambda(1405)$ resonance. In the second case many resonances are also generated, among them an exotic baryon with S=1 corresponding to a $\Delta K$ resonance. We make suggestions of experiments which could show evidence for the existence of these states.
Two-photon and one-photon–one-vector meson decay widths of thef0(1370),f2(1270),f0(1710),f2′(1525), andK2*(1430)
2010
We calculate the radiative decay widths, two-photon ($\ensuremath{\gamma}\ensuremath{\gamma}$) and one-photon--one-vector meson ($V\ensuremath{\gamma}$), of the dynamically generated resonances from vector-meson--vector-meson interaction in a unitary approach based on the hidden-gauge Lagrangians. In the present paper we consider the following dynamically generated resonances: ${f}_{0}(1370)$, ${f}_{0}(1710)$, ${f}_{2}(1270)$, ${f}_{2}^{\ensuremath{'}}(1525)$, ${K}_{2}^{*}(1430)$, two $\mathrm{\text{strangeness}}=0$ and $\mathrm{\text{isospin}}=1$ states, and two $\mathrm{\text{strangeness}}=1$ and $\mathrm{\text{isospin}}=1/2$ states. For the ${f}_{0}(1370)$ and ${f}_{2}(1270)$ we reproduc…
Overview of the electromagnetic production of strange mesons at MAMI
2013
Abstract The Mainz Microtron MAMI provides a continuous-wave unpolarized or spin-polarized electron beam with energies up to 1.6 GeV and high degrees of polarization. Electro-production of strange mesons is performed in the multi-spectrometer facility with the Kaos spectrometer for kaon detection and a high-resolution spectrometer for electron detection in plane or out of plane. Differential cross section measurements of exclusive p ( e , e ′ K + ) Λ , Σ 0 reactions at low four-momentum transfers in the nucleonʼs third resonance region have been done, followed by a measurement of the beam helicity asymmetry for p ( e → , e ′ K + ) Λ . These studies are important for the understanding of the…
Re-analysis of theΛ(1520)photoproduction reaction
2014
Based on previous studies that support the important role of the N*(2120)D-13 resonance in the gamma p -> K+ A(1520) reaction, we make a re-analysis of this A(1520) photoproduction reaction taking into account the recent CLAS differential cross-section data. In addition to the contact, t-channel (K) over bar exchange, s-channel nucleon pole, and N*(2120) [previously called N*(2080)] resonance contributions, which have been considered in previous works, we also study the u-channel A(1115) hyperon pole term. The latter mechanism has always been ignored in all theoretical analysis, which has mostly relied on the very forward K+ angular LEPS data. It is shown that when the contributions from th…
First measurements of Λ and hyperons in elementary electroproduction at MAMI
2010
Abstract Since 2008 the magnetic spectrometer Kaos , dedicated to the detection of charged kaons, is operating at the 1.5 GeV electron beam of MAMI at the Institut fur Kernphysik in Mainz, Germany. The strangeness programme performed in 2008–9 is addressing some important issues in the field of elementary kaon photoelectro-production reactions. The identification of Λ and Σ 0 hyperons in the missing mass spectra from kaon production off a liquid hydrogen target demonstrates the capability of the extended facility to perform strangeness electro-production spectroscopy at low momentum transfers Q 2 0.5 ( GeV / c ) 2 . Systematic uncertainties in the cross-section extraction from the data are …
Strange hadronic physics in electroproduction experiments at the Mainz Microtron
2012
Abstract Present and future research into the electroproduction of strangeness plays an important role at Mainz Microtron MAMI. With the Kaos spectrometer for kaon detection operated in the multi-spectrometer facility first cross section measurements of the exclusive p ( e , e ′ K + ) Λ , Σ 0 reactions at low-momentum transfers have been performed. These measurements have clearly discriminated between effective Lagrangian models for photo- and electroproduction of strangeness. Recently, the Kaos spectrometer was upgraded to a double-arm spectrometer for the measurement of elementary cross sections at very forward scattering angles and for the missing mass spectroscopy of hypernuclear states…