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E. Oset

Publications and source records attributed to E. Oset.

At least 325 records · Page 18Linked to original sources
arXiv2008

Radiative decay into $γP$ of the low lying axial-vector mesons

We evaluate the radiative decay into a pseudoscalar meson and a photon of the whole set of the axial-vector mesons dynamically generated from the vector-pseudoscalar meson ($VP$) interaction. We take into account tree level and loop diagrams coming from the axial-vector decay into a vector and a pseudoscalar meson. We find a large span for the values of the radiative widths of the different axial-vector mesons. In particular, we evaluate the radiative decay into $K γ$ of the two $K_1(1270)$ states, recently claimed theoretically, and discuss the experimental values quoted so far on the assumption of only one state.

hep-ph↗
arXiv2008

Meson loops in the $f_0(980)$ and $a_0(980)$ radiative decays into $ρ$, $ω$

We calculate the radiative decay widths of the $a_0(980)$ and $f_0(980)$ scalar mesons into $ργ$ and $ωγ$ considering the dynamically generated nature of these scalar resonances within the realm of the Chiral Unitary Approach. The main ingredient in the evaluation of the radiative width of the scalar mesons are the loops coming from the decay into their constituent pseudoscalar-pseudoscalar components and the subsequent radiation of the photon. The dominant diagrams with only pseudoscalar mesons in the loops are found to be convergent while the divergence of those with a vector meson in the loop are written in terms of the two meson loop function easily regularizable. We provide results for all the possible charge channels and obtain results, with uncertainties, which differ significantly from quark loops models and some version of vector meson dominance.

hep-ph↗
arXiv2008

Photo- and Electron-Production of Mesons on Nucleons and Nuclei

In these lectures I will show some results obtained with the chiral unitary approach applied to the photo and electroproduction of mesons. The results for photoproduction of $ηπ^0 p$ and $K^0 π^0 Σ^+$, together with related reactions will be shown, having with common denominator the excitation of the $Δ(1700)$ resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show results obtained for the $e^+ e^- \to ϕf_0(980)$ reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the $N^*(1535)$ resonance, also dynamically generated in this approach. Finally, I will show some results on the photoproduction of the $ω$ in nuclei, showing that present experimental results claiming a shift of the $ω$ mass in the medium are tied to a particular choice of background and are not conclusive. One the other hand, the same experimental results show unambiguously a huge increase of the $ω$ width in the nuclear medium.

nucl-th↗
arXiv2008

The role of the $Λ(1405)$ in the $pp\to p K^+Λ(1405)$ reaction

We report a theoretical study of the $pp\to p K^+Λ(1405)$ reaction, which was recently investigated at COSY-Jülich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. The reaction is driven by single kaon exchange, single pion exchange, and single rho exchange terms which have very different shapes due to the two pole structure of the $Λ(1405)$ and the presence of background terms. The shape for the sum of the three contributions, as well as the total cross section, are consistent with present data within experimental and theoretical uncertainties, using reasonable form factors for the meson-baryon vertices.

hep-ph↗
arXiv2008

$η\to π^0 γγ$ decay within a chiral unitary approach revisited

In view of the recent experimental developments on the experimental side in the $η\to π^0 γγ$ decay, and the fact that the Particle Data Group in the on line edition of 2007 reports sizable changes of the radiative decay widths of vector mesons used as input in the theoretical calculations of \cite{eta}, a reevaluation of the decay width of the $η$ in this channel has been done, reducing its uncertainty by almost a factor of two. The new input of the PDG is used and invariant mass distributions and total widths are compared with the most recent results from AGS, MAMI and preliminary ones of KLOE. The agreement of the theory with the AGS and MAMI data is very good, both for the total rates as well as for the invariant mass distributions of the two photons.

hep-ph↗
arXiv2007

Recent Developments in Chiral Unitary Dynamics of Resonances

In this talk I summarize recent findings made on the description of axial vector mesons as dynamically generated states from the interaction of peseudoscalar mesons and vector mesons, dedicating some attention to the two $K_1(1270)$ states. Then I review the generation of open and hidden charm scalar and axial states. Finally, I present recent results showing that the low lying $1/2^+$ baryon resonances for S=-1 can be obtained as bound states or resonances of two mesons and one baryon in coupled channels dynamics.

nucl-th↗
arXiv2007

Hidden charm dynamically generated resonances and the $e^+e^-\to J/ψD \bar D$, $J/ψD\bar D^*$ reactions

We analyze two recent reactions of Belle, producing $D\bar D$ and $D\bar D^*$ states that have an enhancement of the invariant $D\bar D$, $D\bar D^*$ mass distribution close to threshold, from the point of view that they might be indicative of the existence of a hidden charm scalar and an axial vector meson states below $D\bar D$ or $D\bar D^*$ thresholds, respectively. We conclude that the data is compatible with the existing prediction of a hidden charm scalar meson with mass around 3700 MeV, though other possibilities cannot be discarded. The peak seen in the $D\bar D^*$ spectrum above threshold is, however, unlikely to be due to a threshold enhancement produced by the presence, below threshold, of the hidden charm axial vector meson X(3872).

hep-ph↗
arXiv2007

The WA3 data and the two $K_1(1270)$ resonances

Recent studies based on unitary chiral perturbation theory (U$χ$PT) found that the low-lying axial vector mesons can be dynamically generated due to the interaction of the pseudoscalar octet of the pion and the vector nonet of the rho. In particular, two poles in the second Riemann sheet have been associated to the nominal $K_1(1270)$ resonance. In this talk, we present a recent analysis of the WA3 data on $K^-p\to K^-π^+π^- p$ at 63 GeV using the U$χ$PT amplitudes, and show that it is in favor of the existence of two $K_1(1270)$'s [Phys. Rev. D 75, 014017 (2007)].

hep-ph↗
arXiv2007

Resonances in chiral unitary approaches

The extension of chiral theories to the description of resonances, via the incorporation of unitarity in coupled channels, has provided us with a new theoretical perspective on the nature of some of the observed excited hadrons. In this contribution some of the early achievements in the field of baryonic resonances are reviewed, the recent evidence of the two-pole nature of the Lambda(1405) is discussed and results on charmed baryon resonances are presented.

nucl-th↗
arXiv2007

Dynamically generated open and hidden charm mesons

In this presentation I explain our framework for dynamically generating resonances from the meson meson interaction. Our model generates many poles in the T-matrix which are associated with known states, while at the same time new states are predicted.

hep-ph↗
arXiv2007

The nature of the Lambda(1405)

We present here some results supporting the nature of the $Λ(1405)$ resonance as dynamically generated from the meson baryon interaction in coupled channels and resulting from the superposition of two close-by poles. We find support for this picture in the $K^- p \to π^0 π^0 Σ^0 $ reaction, which shows a different shape than the one obtained from the $π^- p \to K^0 πΣ$ reaction. We also call the attention to the $K^- p \to γπΣ$ with $πΣ$ in the $Λ(1405)$ region, which shows a narrow peak in the calculations around 1420 MeV. We also report on recent calculations of the radiative decay of the two $Λ(1405)$ states and on reactions to obtain information on these decay modes. Finally, we present results for the $pp\to p K^+Λ(1405)$ reaction recently measured at ANKE/COSY and compare them with theoretical results.

nucl-th↗
arXiv2007

Electron-positron annihilation into phi f_{0}(980) and clues for a new 1^{--} resonance

We study the e^{+}e^{-} to phi pi pi reaction for pions in an isoscalar s-wave which is dominated by loop mechanisms. For kaon loops we start from the conventional RCHPT, but use the unitarized amplitude for KbarK-pipi scattering and the full kaon form factor instead of the lowest order terms. We study also effects of vector mesons using RCHPT supplemented with the conventional anomalous term for VVP interactions and taking into account the effects of heavy vector mesons in the K*K transition form factor. We find a peak in the dipion invariant mass around the f_{0}(980) as in the experiment. Selecting the phi f_{0}(980) contribution as a function of the e^{+}e^{-} energy we also reproduce the experimental data except for a narrow peak, yielding support to the existence of a 1^{--} resonance above the phi f_{0}(980) threshold, coupling strongly to this state.

hep-ph↗
arXiv2007

Photoproduction of $ω$ and $ω$ in the Nuclear Medium

We reanalyze data from ELSA on $ω$ production in nuclei, from where claims of a large shift of the mass were made earlier, which are tied to a certain election of the background in nuclei, very different in shape to the one on the proton. The reanalysis shows that the data demand a very large width of the $ω$ in the medium, with no need for a shift of the mass, for which the experiment is quite insensitive. We study possible $ω$ bound states in the nucleus and find that, even assuming a small width, they could not be observed with the present ELSA resolution. Finally we show that, due to the interplay of background and $ω$ signal, a two bump structure appears with the ELSA set up for the $(γ,p)$ reaction that should not be misidentified with a signal of a possible $ω$ bound state in the nucleus.

nucl-th↗
arXiv2007

Quantum loops in radiative decays of the $a_1$ and $b_1$ axial-vector mesons

A previous model where the low-lying axial-vector mesons are dynamically generated, implementing unitarity in coupled channels in the vector-pseudoscalar ($VP$) meson interaction, is applied to evaluate the decay widths of the a_1(1260)$ and $b_1(1235)$ axial-vector mesons into $πγ$. Unlike the case of the $a_1$, the $b_1$ radiative decay is systematically underestimated at tree level. In this work we evaluate for the first time the loop contribution coming from an initial $VP$ vertex. Despite the large superficial divergence of the loops, the convergence of the relevant loops can be established by using arguments of gauge invariance. The partial decay widths obtained agree very well with the experimental values within uncertainties, and show that the loop contribution is crucial in the $b_1$ case and also important for the $a_1$ case.

hep-ph↗
arXiv2007

The radiative decay of the $Λ(1405)$ and its two-pole structure

We evaluate theoretically the radiative decay widths into $γΛ$ and $γΣ^0$ of the two poles of the $Λ(1405)$ found in chiral unitary theories and we find quite different results for each of the two poles. We show that, depending on which reaction is used to measure the $Λ(1405)$ radiative decays, one gives more weight to one or the other pole, resulting in quite different shapes in the $γΛ(Σ^0)$ invariant mass distributions. Our results for the high-energy pole agree with those of the empirical determination of the $γΛ$ and $γΣ^0$ radiative widths (based on an isobar model fitting of the $K^-p$ atom data), which are sometimes referred to as ``experimental data''. We have made a detailed study of the $K^-p\toπ^0γΛ(Σ^0)$ and $π^-p\to K^0γΛ(Σ^0)$ reactions and have shown that they, indeed, lead to different shapes for the $γΛ(Σ^0)$ invariant mass distributions.

hep-ph↗
arXiv2007

Dynamically Generated Open and Hidden Charm Meson Systems

We will study open and hidden charm scalar meson resonances within two different models. The first one is a direct application of a chiral Lagrangian already used to study flavor symmetry breaking in Skyrme models. In another approach to the problem a SU(4) symmetric Lagrangian is built and the symmetry is broken down to SU(3) by identifying currents where heavy mesons are exchanged and suppressing those. Unitarization in couple channels leads to dynamical generation of resonances in both models, in particular a new hidden charm resonance with mass 3.7 GeV is predicted. The small differences between these models and with previous works will be discussed.

hep-ph↗