Search results for "hyperon"
showing 10 items of 118 documents
V-us determination from hyperon semileptonic decays
2005
16 páginas, 9 tablas.-- arXiv:hep-ph/0509045v2
Chiral dynamics of thepwave inK−pand coupled states
2002
We perform an evaluation of the p-wave amplitudes of meson-baryon scattering in the strangeness $S=\ensuremath{-}1$ sector starting from the lowest order chiral Lagrangians and introducing explicitly the ${\ensuremath{\Sigma}}^{*}$ field with couplings to the meson-baryon states obtained using SU(6) symmetry. The $N/D$ method of unitarization is used, equivalent, in practice, to the use of the Bethe-Salpeter equation with a cutoff. The procedure leaves no freedom for the p-waves once the s-waves are fixed and thus one obtains genuine predictions for the p-wave scattering amplitudes, which are in good agreement with experimental results for differential cross sections, as well as for the wid…
EXTRACTION OF THE Λ(1405) POLES FROM π0Σ0 PHOTOPRODUCTION DATA
2014
In this contribution we review a work where we showed how to extract the position of the two Λ(1405) poles from experimental photoproduction data which have been measured recently in the γp → K+π0Σ0 reaction at Jefferson Lab. Using a potential motivated by chiral dynamics but with free parameters, we solve the Bethe Salpeter equation in the coupled channels [Formula: see text] and πΣ in isospin I=0 and parameterize the amplitude for the photonuclear reaction in terms of a linear combination of the πΣ → πΣ and [Formula: see text] scattering amplitudes in I=0, with a different linear combination for each energy. Good fits to the data are obtained which lead to two poles at 1385 - 68i MeV and…
Electroproduction of hyperons
1997
Abstract We present some estimates for the reaction ep → e ′ Σ + . At small scattering angles, the differential cross section is completely determined by the experimental data for the radiative decay Σ + → pγ . For kinematical values typical of the proposed parity experiment at MAMI, we find a suppression factor of about 5 · 10 −15 as compared to elastic electron scattering. On the basis of conservative models for the transition form factors, this ratio might increase by about a factor of 20 at backward angles. Even higher values could be expected if the presently unknown convection currents should turn out to be large. Due to the parity violation involved in this process, we also expect a …
The RICH counter in the CERN hyperon beam experiment
1992
Abstract The hyperon beam experiment WA89 at the CERN-SPS uses a ring imaging Cherenkov counter (RICH) for identification of secondaries from ∑ − N reactions. Cherenkov photons are generated in a 5 m long radiator volume filled with nitrogen at atmospheric pressure and detected in drift chambers. The drift chambers cover an active surface of 1.6 × 0.75 m 2 , with a maximum drift path of 41 cm. Photoelectrons are counted on 1280 wires with a pitch of 2.54 mm, equipped with multihit TDCs. The counting gas is ethane saturated with TMAE at 30°C. The counter was operated in two beam periods in 1990 and 1991. The spatial resolution of the chambers is better than 2 mm and under normal running cond…
QCD sum rule analysis of the pentaquark
2005
We perform a QCD sum rule calculation to determine the mass and the parity of the lowest lying pentaquark state. We include operators up to dimension $d=13$ in the OPE and the direct instanton contributions. We find evidence for a positive parity state. The contribution from operators of dimension $d>5$ is instrumental in determining the parity of the state and achieving the convergence of the sum rule.
SU(3)-breaking corrections to the hyperon vector couplingf1(0)in covariant baryon chiral perturbation theory
2009
This work was partially supported by the MEC Grant No. FIS2006-03438 and the European Community- Research Infrastructure Integrating Activity Study of Strongly Interacting Matter (Hadron-Physics2, Grant Agreement 227431) under the Seventh Framework Programme of EU. L. S. G. acknowledges support from the MICINN in the Program ‘‘Juan de la Cierva.’’ J. M. C. acknowledges the same institution for an FPU grant.
Measurement of hadron form factors at BESIII
2018
The BESIII experiment, operated at the BEPCII e+e- collider in Beijing, has acquired large data sets at center-of-mass energies between 2.0 GeV and 4.6 GeV. One of the key aspects of the physics program of the BESIII collaboration is to test the understanding of QCD at intermediate energies. Applying different experimental techniques, form factors of hadrons are measured. Among these are the pion form factor, as an important input to the (g - 2)μ puzzle, and the electro-magnetic form factors of nucleons and hyperons in the time-like regime. An overview of the recent results and some ongoing studies at BESIII is provided.
Tensor charges and form factors of SU(3) baryons in the self-consistent SU(3) chiral quark-soliton model
2010
We investigate the tensor form factors of the baryon octet within the framework of the chiral quark-soliton model, emphasizing those of the nucleon, taking linear 1/N_c rotational as well as linear m_s corrections into account, and applying the symmetry-conserving quantization. We explicitly calculate the tensor form factors H_{T}^{q}(Q^{2}) corresponding to the generalized parton distributions H_{T}(x,\xi,t). The tensor form factors are obtained for the momentum transfer up to Q^{2}\leq1\,\mathrm{GeV}^{2} and at a renormalization scale of 0.36\,\mathrm{GeV}^{2}. We find for the tensor charges \delta u=1.08, \delta d=-0.32, \delta s=-0.01 and discuss their physical consequences, comparing t…
Quark mass dependence of s-wave baryon resonances
2003
We study the quark mass dependence of $J^P = \frac12^-$ s-wave baryon resonances. Parameter free results are obtained in terms of the leading order chiral Lagrangian. In the 'heavy' SU(3) limit with $m_\pi =m_K \simeq $ 500 MeV the resonances turn into bound states forming two octets plus a singlet representations of the SU(3) group. A contrasted result is obtained in the 'light' SU(3) limit with $m_\pi =m_K \simeq $ 140 MeV for which no resonances exist. Using physical quark masses our analysis suggests to assign to the $S=-2$ resonances $\Xi(1690)$ and $\Xi(1620)$ the quantum numbers $J^P=1/2^-$.