0000000000613372
AUTHOR
Manuel José Vicente Vacas
Baryonic Resonances from Baryon Decuplet-Meson Octet Interactions and the Exotic Resonance S=1, I=1, J^P=3/2-
Using the lowest order chiral Lagrangian we study s-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons. We find two bound states in the flavour SU(3) limit corresponding to the octet and decuplet representations. These are found to split into eight different trajectories in the complex plane when the SU(3) symmetry is broken gradually. Finally, we are able to provide a reasonable description for a good number of 4-star 3/2- resonances listed by the Particle Data Group. In particular, the Xi(1820), the Lambda(1520) and the Sigma(1670) states are well reproduced. We predict a few other resonances and also evaluate the couplings of the observed resonances to the var…
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.
S=-1 meson-baryon unitarized coupled channel chiral perturbation theory and the S-01 resonances Lambda(1405) and -Lambda(1670)
The s-wave meson-baryon scattering is analyzed for the strangeness S=-1 and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism incorporating chiral symmetry. Four channels have been considered: piSigma, (K) over barN, etaLambda, and KXi. The required input to solve the Bethe-Salpeter equation is taken from lowest order chiral perturbation theory in a relativistic formalism. There appear undetermined low energy constants, as a consequence of the renormalization of the amplitudes, which are obtained from fits to the piSigma-->piSigma mass spectrum, to the elastic (K) over barN-->(K) over barN and (K) over barN-->piSigma t matrices and to the K(-)p-->etaLambda cross section data.…
Octet-baryon axial-vector charges and SU(3)-breaking effects in the semileptonic hyperon decays
The octet-baryon axial-vector charges and the g(1)/f(1) ratios measured in the semileptonic hyperon decays are studied up to O(p(3)) using the covariant baryon chiral perturbation theory with explicit decuplet contributions. We clarify the role of different low-energy constants and find a good convergence for the chiral expansion of the axial-vector charges of the baryon octet, g(1)(0), with O(p(3)) corrections typically around 20% of the leading ones. This is a consequence of strong cancellations between different next-to-leading- order terms. We show that considering only nonanalytic terms is not enough and that analytic terms appearing at the same chiral order play an important role in t…
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.
SU(3)-breaking corrections to the hyperon vector coupling f(1)(0) in covariant baryon chiral perturbation theory
We calculate the SU(3)-breaking corrections to the hyperon vector coupling f(1)(0) up to O(p(4)) in covariant baryon chiral perturbation theory with dynamical octet and decuplet contributions. We find that the decuplet contributions are of similar or even larger size than the octet ones. Combining both, we predict positive SU(3)-breaking corrections to all the four independent f(1)(0)'s (assuming isospin symmetry), which are consistent, within uncertainties, with the latest results from large N-c fits, chiral quark models, and quenched lattice QCD calculations.
Scalar isoscalar pion pairs in nuclei and the A(pi,pi pi)X reaction
The reaction A(pi,pi pi)X has been studied at low energies, paying particular attention to the interaction of the two final pions in the scalar isoscalar (I=J=0) channel. We have developed a microscopic model for the pion production, and then implemented the two pion final state interaction by using the results of a non-perturbative unitary coupled-channels method based in the standard chiral Lagrangians. The resulting model, describes well the reaction on the nucleon for all different isospin channels. Finally, we have considered the reaction in nuclei. Our calculation takes into account Fermi motion, Pauli blocking, pion absorption, and also the strong modification of the pi-pi interactio…
Theta(+) hypernuclei
We present results for the selfenergy of the Theta(+) pentaquark in nuclei associated with two sources: the KN decay of the Theta(+) and the two meson baryon decay channels of the Theta(+) partners in an antidecuplet of baryons. The first source is shown to produce a small potential, unable to bind the Theta(+) in nuclei, while the second source gives rise to a large attractive potential. At the same tune we show that the width of the Theta(+) in nuclei is small, such that, in light and medium nuclei, many bound Theta(+) states would appear with a separation between levels appreciably larger than the width of the states, thus creating an ideal scenario for pentaquark spectroscopy in nuclei.
Nuclear medium modification of the F(2) structure function
We study the nuclear effects in the electromagnetic structure function F-2(x, Q(2)) in the deep inelastic lepton nucleus scattering process by taking into account Fermi motion, binding, pion and rho meson cloud contributions. Calculations have been done in a local density approximation using relativistic nuclear spectral functions which include nucleon correlations. The ratios R-F2(A) (x, Q(2)) = 2F(2)(A)(x, Q(2))/AF(2)(D)(x, Q(2)) are obtained and compared with recent JLab results for light nuclei with special attention to the slope of the x distributions. This magnitude shows a non-trivial A dependence and it is insensitive to possible normalization uncertainties. The results have also be…
Chiral dynamics in the (gamma)over-right-arrowp -> p pi(0) reaction
We investigate the neutral pion photoproduction on the proton near threshold in covariant chiral perturbation theory with the explicit inclusion of A degrees of freedom. This channel is specially sensitive to chiral dynamics and the advent of very precise data from the Mainz microtron has shown the limits of the convergence of the chiral series for both the heavy baryon and the covariant approaches. We show that the inclusion of the Delta resonance substantially improves the convergence leading to a good agreement with data for a wider range of energies.
An anomaly in inclusive pion double charge exchange on 16O at about 1GeV
The new results on the inclusive double charge exchange (DCX) reaction 16O(π-,π+)X at incident kinetic energy T0=0.75 and 1.15GeV are presented. The data were taken without using Cherentov counters. The new DCX cross sections agree well with the old ones. Both the values are about an order of magnitude larger than the theoretical cross sections calculated for the standard sequential mechanism. Two other approaches wich seem to explain the discrepancy are also briefly reviewed. Vicente Vacas, Manuel Jose, Manuel.J.Vicente@ific.uv.es
Chiral symmetry in the KḰ and kn systems
In this talk we present teh results of recent developments in the aplication of Chiral perturbation theory to the KḰ system and to de K+N →KNπ reaction close to threshosd. In the first case, we study the decay channels of the a0 and f0 mesons assumed to be made largely from KḰ. In the second case comparison is made with the present data. A qualitative agreement with experiment is both in found cases. Oset Baguena, Eulogio, Eulogio.Oset@ific.uv.es, Nieves Pamplona, Juan Miguel, Juan.M.Nieves@ific.uv.es
Nu induced threshold production of two pions and N* (1440) electroweak form factors
We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon, pion, and contact terms are calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account. The numerical results for the cross sections are presented and compared with the available experimental data. It has been found that in the two-pion channels with pi(+)pi(-) and pi(0)pi(0) in the final state, the contribution of the N* (1440) is quite important and could be used to determine the N* (1440) electroweak transition form factors if experimental data with better statistics become available in the …
Pion double charge exchange reactions leading to deeply bound double pionic atoms
We study theoretically pion double charge exchange reactions leading to double pionic atoms. The reaction cross-sections with two pions in the deeper bound pionic orbits in 208Pb are calculated with realistic pionic atom wave functions and distortion effects. The cross-sections are found to be d2σ/dEdΩ~10−3−10−4 µb/srMeV, which are only a small fraction of the double charge exchange background.
Isoscalar S-wave π–π interaction in the nuclear medium
The s-wave isoscalar π π scattering amplitude in a nuclear medium has been evaluated using a non-perturbative unitary coupled channels method and the standard chiral Lagrangians. The method is successful describing the π π properties in vacuum, in the scalar-isoscalar channel up to 1.2 GeV giving rise to poles in the T matrix for the ƒ0(980) and the σ. The extension of the method to the nuclear medium implies the renormalization of the pions in the medium and also the introduction of interaction terms related to contact terms in the πN → ππN reaction. Vicente Vacas, Manuel Jose, Manuel.J.Vicente@ific.uv.es ; Oset Baguena , Eulogio, Eulogio.Oset@ific.uv.es
S-wave pion nucleon scattering lengths from $\pi N$, pionic hydrogen and deuteron data
The isoscalar and isovector scattering lengths (b_0,b_1) are determined using a unitarized coupled channel approach based on chiral Lagrangians. Using experimental values of pionic hydrogen and deuterium as well as low energy pi N scattering data, the free parameters of the model are calculated. Isospin violation is incorporated to a certain extent by working with physical particle masses. For the deuterium scattering length a_{pi-d} new significant corrections concerning real and imaginary parts are evaluated, putting new constraints from pi-d scattering on the values of (b_0,b_1). In particular, dispersion corrections, the influence of the Delta(1232) resonance, crossed terms and multiple…
Renormalization of the f(0)(980) and a(0)(980) scalar resonances in a nuclear medium
The meson-meson interaction in the scalar sector in the presence of a nuclear medium is studied with particular attention to the change of the properties of the f(0)(980) and a(0)(980) resonances. By using a chiral unitary approach which generates the f(0) and a(0) resonances and reproduces their free properties, we find that the position of the resonances in the medium is barely changed but their widths are considerably broadened. New many body corrections generating from higher orders in the chiral Lagrangian plus the contribution from N*h excitations, not considered before in connection with the pi pi interaction in the nuclear medium, are also investigated.
nu d ->mu(-)Delta(++)n reaction and axial vector N-Delta coupling
The reaction vd --> mu(-)Delta(++)n is studied in the region of low q(2) to investigate the effect of deuteron structure and width of the Delta resonance on the differential cross section. The results are used to extract the axial vector N-Delta coupling C(5)(A) from the experimental data on this reaction. The possibility to determine this coupling from electroweak interaction experiments with high intensity electron accelerators is discussed.
Bound states of Theta(+) in nuclei
We study the binding energy and the width of the Theta(+) in nuclei, associated to the KN and K pi N components. The first one leads to negligible contributions while the second one leads to a sizeable attraction, enough to bind the Theta(+) in nuclei. Pauli blocking and binding effects on the KN decay reduce considerably the Theta(+) decay width in nuclei and medium effects associated to the K pi N component also lead to a very small width, as a consequence of which one finds separation between the bound levels considerably larger than the width of the states.
Nuclear medium effects in nu(nu)-nucleus deep inelastic scattering
We study nuclear medium effects in the weak structure functions F-2(x, Q(2)) and F-3(x, Q(2)) in the deep inelastic neutrino and antineutrino induced reactions in nuclei. We use a theoretical model for the nuclear spectral functions which incorporates the conventional nuclear effects, such as Fermi motion, binding, and nucleon correlations. We also consider the pion and rho meson cloud contributions calculated from a microscopic model for meson-nucleus self-energies. The calculations have been performed using relativistic nuclear spectral functions. Our results are compared with the experimental data of the NuTeV and the CERN Dortmund Heidelberg Saclay Warsaw (CDHSW) collaborations.
Recent developments in one and two pion production in elementary reactions and few-body systems
In this talk we cover several issues concerning pion production. The first one is the p p ----> p p pi^0 reaction where an alternative explanation based on the off shell extrapolation of the pi N amplitude is offered. A recent model for the gamma N ----> pi pi N reaction is presented and a new kind of exchange current is constructed from it which allows one to address problems like double Delta photoproduction from the deuteron. Finally the (gamma, pi pi) reaction in nuclei is studied and shown to be highly sensitive to the renormalization of the pions in nuclei.
Photoproduction of $K^*$ for the study of $\Lambda(1405)$
The photo-induced $K^*$ vector meson production is investigated for the study of the $\Lambda(1405)$ resonance. This reaction is particularly suited to the isolation of the second pole in the $\Lambda(1405)$ region which couples dominantly to the $\bar K N$ channel. We obtain the mass distribution of the $\Lambda(1405)$ which peaks at 1420 MeV, and differs from the nominal one. Combined with several other reactions, like the $\pi^- p \to K^0 \pi \Sigma$ which favours the first pole, this detailed study will reveal a novel structure of the $\Lambda(1405)$ state.
Light scalar mesons in J/psi -> N(N)over-bar meson meson decays in a chiral unitary approach
We study the four-body decays J/psi --> N(N) over bar meson meson using a chiral unitary approach to account for the meson meson final state interaction (FSI). The calculation of the J/psi --> N(N) over bar pi(+)pi(-) process properly reproduces the experimental data after taking the FSI of mesons and the contribution of intermediate rho meson into account. The isoscalar resonances sigma,f(0)(980) and the isovector resonance a(0)(980) are generated through the FSI of the mesons in the channels J/psi --> N(N) over bar pi(0)pi(0) and J/psi --> N(N) over bar pi(0)eta, respectively. We also calculate the two mesons invariant mass distribution and the partial decay width of J/psi --> N(N) over b…
(nu)over-bar induced (K)over-bar production off the nucleon
The charged-current antikaon production off nucleons induced by antineutrinos is studied at low and intermediate energies. We extend here our previous calculation on kaon production induced by neutrinos. We have developed a microscopic model that starts from the SU(3) chiral Lagrangians and includes background terms and the resonant mechanisms associated to the lowest lying resonance in the channel, namely, the Sigma*(1385). Our results could be of interest for the background estimation of various neutrino oscillation experiments like MiniBooNE and SuperK. They can also be helpful for the planned (nu) over bar experiments like MINER nu A, NO nu A, and T2K phase II, and for beta-beam experim…