0000000000204030
AUTHOR
ÀNgels Ramos Gómez
Transparency ratio in gamma A -> eta ' A ' and the in-medium eta ' width
The photoproduction of \eta'-mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500 - 2200 MeV. The transparency ratio has been deduced and compared to theoretical calculations describing the propagation of \eta'-mesons in nuclei. The comparison indicates a width of the \eta' -meson of the order of \Gamma= 15-25 MeV at \rho =\rho_0 for an average momentum p_{\eta'} = 1050 MeV/c, at which the \eta'-meson is produced in the nuclear rest frame. The inelastic \eta' N cross section is estimated to be 3 - 10 mb. Parameterizing the photoproduction cross section of \eta'-mesons by \sigma(A) = \sigma_0 A^{\alpha}, a value of \alph…
phi decay in nuclei
We have studied the decay of the \phi meson in nuclear matter by taking into account the renormalization of the K and \bar{K} mesons in the medium. We separate the contribution of the total width into different reaction channels, K\bar{K} and KYh, the latter ones associated with the \phi N \to K^+ Y reactions. We find a total width at normal nuclear matter density of about 22 MeV, considerably larger than the free one.
Non-perturbative chiral approach to K(-)p ->gamma Y reactions
A recently developed nonperturbative chiral approach to describe the S=-1 meson-baryon reactions has been extended to investigate the near threshold K−p→γΛ,γΣ0 reactions. With the parameters governed by chiral SU(3) symmetry, we show that the predicted branching ratios ΓK−p→γΛ/ΓK−p→all and ΓK−p→γΣ0/ΓK−p→all are close to the experimental values. The coupling with the η channels, which was shown to be important in the S=−1 meson-baryon reactions, is also found to be significant here. Our results are consistent with the interpretation of the Λ(1405) as a quasi-bound meson-baryon state as found in other similar chiral approaches.
Chiral dynamics of the p wave in K(-)p and coupled states
We perform an evaluation of the p-wave amplitudes of meson-baryon scattering in the strangeness S=-1 sector starting from the lowest order chiral Lagrangians and introducing explicitly the 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 cut-off. 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 width and partial decay widths of the S…
Chiral Dynamics of Hadrons in Nuclei
In this talk I report on selected topics of hadron modification in the nuclear medium using the chiral unitary approach to describe the dynamics of the problems. I shall mention how antikaons, $\eta$, and $\phi$ are modified in the medium and will report upon different experiments done or planned to measure the $\phi$ width in the medium.
Lambda(b) -> J/psi K Xi decay and the higher order chiral terms of the meson baryon interaction
We study the weak decay of the Lambda(b) into J/psi K Xi. and J/psi eta Lambda states, and relate these processes to the Lambda(b) -> J/psi(K) over barN decay mode. The elementary weak transition at the quark level proceeds via the creation of a J/psi meson and an excited sud system with I = 0, which upon hadronization leads to (K) over barN or eta Lambda pairs. These states undergo final-state interaction in coupled channels and produce a final meson-baryon pair. The K. state only occurs via rescattering, hence making the Lambda(b) -> J/psi K Xi process very sensitive to the details of the meson-baryon interaction in strangeness S = -1 and isospin I = 0. We show that the corresponding inva…
Lambda(1405) production in the pi-p -> K-0 pi Sigma reaction
We discuss the mechanisms that lead to Lambda(1405) production in the pi(-)p-->K(0)piSigma reaction. The problem has gained renewed interest after different works converge to the conclusion that there are two resonances around the region of 1400 MeV, rather than one, and that they couple differently to the piSigma and (K) over barN channels. We look at the dynamics of that reaction and find two mechanisms which eventually filter each one of the resonances, leading to very different shapes of the piSigma invariant mass distributions. The combination of the two mechanisms leads to a shape of this distribution compatible with the experimental measurements.
Reanalysis of lattice QCD spectra leading to the Ds0*(2317) and Ds1*(2460)
We perform a reanalysis of the energy levels obtained in a recent lattice QCD simulation, from where the existence of bound states of KD and KD* are induced and identified with the narrow D-s0*(2317) and D-s1*(2460) resonances. The reanalysis is done in terms of an auxiliary potential, employing a single-channel basis KD(*()), and a two-channel basis KD(*()), eta D-s(()*()). By means of an extended Luscher method we determine poles of the continuum t-matrix, bound by about 40 MeV with respect to the KD and KD* thresholds, which we identify with the D-s0*(2317) and D-s1*(2460) resonances. Using a sum rule that reformulates Weinberg compositeness condition we can determine that the state D-s0…
Chiral approach to antikaon s- and p-wave interactions in dense nuclear matter
The properties of the antikaons in nuclear matter are investigated from a chiral unitary approach which incorporates the s- and p-waves of the ${\bar K}N$ interaction. To obtain the in-medium meson-baryon amplitudes we include, in a self-consistent way, Pauli blocking effects, meson self-energies corrected by nuclear short-range correlations and baryon binding potentials. We pay special attention to investigating the validity of the on-shell factorization, showing that it cannot be applied in the evaluation of the in-medium corrections to the p-wave amplitudes. In nuclear matter at saturation energy, the $\Lambda$ and $\Sigma$ develop an attractive potential of about -30 MeV, while the $\Si…
(K)over-bar* mesons in dense matter
We study the properties of (K) over bar* mesons in nuclear matter using a unitary approach in coupled channels within the framework of the local hidden gauge formalism and incorporating the (K) over bar pi decay channel in matter. The in-medium (K) over bar *N interaction accounts for Pauli blocking effects and incorporates the (K) over bar* self-energy in a self-consistent manner. We also obtain the (K) over bar* (off-shell) spectral function and analyze its behavior at finite density and momentum. At a normal nuclear matter density, the (K) over bar* meson feels a moderately attractive potential, while the (K) over bar* width becomes five times larger than in free space. We estimate the t…
Neutron and proton spectra from the decay of Lambda hypernuclei
We have determined the spectra of neutrons and protons following the decay of $\Lambda$ hypernuclei through the one- and two-nucleon induced mechanisms. The momentum distributions of the primary nucleons are calculated and a Monte Carlo simulation is used to account for final state interactions. From the spectra we calculate the number of neutrons ($N_n$) and protons ($N_p$) per $\Lambda$ decay and show how the measurement of these quantities, particularly $N_p$, can lead to a determination of $\Gamma_n / \Gamma_p$, the ratio of neutron to proton induced $\Lambda$ decay. We also show that the consideration of the two-nucleon induced channel has a repercussion in the results, widening the ba…
eta '-Nucleus optical potential and possible eta ' bound states
Starting from a recent model of the eta'N interaction, we evaluate the eta'-nucleus optical potential, including the contribution of lowest order in density, t rho/2m(eta'), together with the second-order terms accounting for eta' absorption by two nucleons. We also calculate the formation cross section of the eta' bound states from (pi(+), p) reactions on nuclei. The eta'-nucleus potential suffers from uncertainties tied to the poorly known eta'N interaction, which can be partially constrained by the experimental modulus of the eta'N scattering length and/or the recently measured transparency ratios in eta' nuclear photoproduction. Assuming an attractive interaction and taking the claimed …
Weak Decay of Lambda Hypernuclei
We review recent developments concerning the weak decay of Lambda hypernuclei. New studies covering the mesonic decay channel as well as recent models for the non-mesonic one are discussed and compared with experimental data. The puzzle of the neutron- to proton-induced decay ratio, Gamma_n/Gamma_p, is addressed in connection to the two-nucleon induced decay channel and proposals for more efficient experimental analyses of this ratio are made.
The properties of (K)over-bar in the nuclear medium
The self-energy of the K^- meson in nuclear matter is calculated in a self-consistent microscopic approach, using a \bar{K}N interaction obtained from the lowest-order meson-baryon chiral Lagrangian. The effective \bar{K}N interaction in the medium is derived by solving the coupled-channel Bethe-Salpeter equation including Pauli blocking on the nucleons, mean-field binding potentials for the baryons and the self-energy of the \pi and \bar{K} mesons. The incorporation of the self-consistent {\bar K} self-energy in the description, in addition to the Pauli blocking effects, yields a weaker attractive in-medium {\bar K}N interaction and a \Lambda(1405) which dissolves faster with increasing ma…
Non-perturbative chiral approach to s-wave (K)over-barN interactions
The s-wave meson-nucleon interaction in the S=−1 sector is studied by means of coupled-channel Lippmann Schwinger equations, using the lowest order chiral Lagrangian and a cut off to regularize the loop integrals. The method reproduces succesfully the Λ(1405) resonance and the K−p→K−p,K¯0n,π0Λ,π0Σ,π+Σ−,π−Σ+ cross sections at low energies. The inclusion of the ηΛ,ηΣ0 channels in the coupled system is found very important and allows a solution in terms of only the lowest order Lagrangian.
Nuclear medium effects on the (K)over-bar* meson
The K¯∗ meson in dense matter is analyzed by means of a unitary approach in coupled channels based on the local hidden gauge formalism. The K¯∗ self-energy and the corresponding K¯∗ spectral function in the nuclear medium are obtained. We observe that the K¯∗ develops a width in matter up to five times bigger than in free space. We also estimate the transparency ratio of the γA→K+K∗−A′ reaction. This ratio is an excellent tool to detect experimentally modifications of the K¯∗ meson in dense matter.
Meson–meson and meson–baryon interactions in a chiral non-perturbative approach
A qualitative account of the meson-meson and meson-baryon interactions using chiral Lagrangians and the inverse amplitude method in coupled channels is done. The method, imposing exact unitarity, proves to be a very useful tool to extend the information contained in the chiral Lagrangians at energies beyond the realm of applicability of chiral perturbation theory. Oset Baguena, Eulogio, Eulogio.Oset@ific.uv.es
The role of vector-baryon channels and resonances in the γp→K0Σ+ and γn→K0Σ0 reactions near the K⁎Λ threshold
AbstractWe have studied the γp→K0Σ+ reaction in the energy region around the K⁎Λ and K⁎Σ thresholds, where the CBELSA/TAPS cross section shows a sudden drop and the differential cross section experiences a transition from a forward-peaked distribution to a flat one. Our coupled-channel model incorporates the dynamics of the vector meson–baryon interaction which is obtained from the hidden gauge formalism. We find that the cross section in this energy region results from a delicate interference between amplitudes having K⁎Λ and K⁎Σ intermediate states. The sharp downfall is dictated by the presence of a nearby N⁎ resonance produced by our model, a feature that we have employed to predict its…
Chiral unitary approach to the pi N*N*, eta N*N* couplings for the N* (1535) resonance
Using a chiral unitary model in which the negative parity nucleon resonance N∗≡N∗(1535) is generated dynamically by means of the Bethe Salpeter equation with coupled meson baryon channels in the S=0 sector, we have obtained the π0N∗N∗ and ηN∗N∗ couplings. The π0N∗N∗ coupling has smaller strength and the same sign as the π0NN coupling. This rules out the mirror assignment of chiral symmetry where the ground state nucleon N and the negative parity resonance N∗ are envisaged as chiral partners in the baryon sector.
Critical view on the deeply bound K- pp system
We briefly review the situation around the claimed deeply bound K^- states in different recent experiments and concentrate particularly on the state K^- pp advocated by the FINUDA collaboration in nuclear K^- absorption. We perform a theoretical simulation of the process and show that the peak in the Lambda p spectrum that was interpreted as a deep K^- pp bound state corresponds mostly to the process K^- p p --> Lambda p followed by final state interactions of the produced particles with the daughter nucleus.