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Now showing items 129 - 144 of 187

  • Sequential vector and axial-vector meson exchange and chiral loops in radiative phi decay

    Palomar, J.E.   Roca, L.   Oset, E.   Vacas, M.J.V.  

    We study the radiative phi decay into pi 0pi 0 gamma and pi 0etagamma taking into account mechanisms in which there are two sequential vector-vector-pseudoscalar or axial-vector-vector-pseudoscalar steps followed by the coupling of a vector meson to the photon, considering the final state interaction of the two mesons. There are other mechanisms in which two kaons are produced through the same sequential mechanisms or from phi decay into two kaons and then undergo final state interaction leading to the final pair of pions or pi 0eta, this latter mechanism being the leading one. The results of the parameter free theory, together with the theoretical uncertainties, are compared with the latest experimental results of KLOE at Frascati
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  • Clues to the nature of the Delta* (1700) resonance from pion- and photon-induced reactions

    Doring, M.   Oset, E.   Strottman, D.  

    We make a study of the pi(-)p -> K(0)pi(0)Lambda, pi(+)p -> K(+)pi(+)Lambda, K(+)(K) over bar (0)p, K(+)pi(+)Sigma(0), K(+)pi(0)Sigma(+), and eta pi(+)p reactions, in which the basic dynamics is given by the excitation of the Delta*(1700) resonance which subsequently decays into K Sigma*(1385) or A(1232)eta. In a similar way we also study the gamma p -> K(0)pi(+)Lambda, K(+)pi(-)Sigma(+), K(+)pi(+)Sigma(-), K(0)pi(0)Sigma(+), and eta pi(0)p related reactions. The cross sections are proportional to the square of the coupling of Delta*(1700) to Sigma*K (Delta eta) for which there is no experimental information but which is provided in the context of coupled channels chiral unitary theory where the Delta*(1700) is dynamically generated. Within present theoretical and experimental uncertainties one can claim a global qualitative agreement between theory and experiment. We provide a list of items which need to be improved in order to make further progress along these lines. (c) 2006 Elsevier B.V. All rights reserved.
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  • The N*(1710) as a resonance in the pi pi N system

    Khemchandani, K. P.   Martinez Torres, A.   Oset, E.  

    We study the pi pi N system by solving the Faddeev equations, for which the input two-body t-matrices are obtained by solving the Bethe-Salpeter equation in the coupled-channel formalism. The potentials for the pi pi, pi N sub-systems and their coupled channels are obtained from chiral Lagrangians, which have been earlier used to study resonances in these systems successfully. In this work, we find a resonance in the pi pi N system with a mass of 1704 - i375/2MeV and with quantum numbers I = 1/2, J(pi) = 1/2(+). We identify this state with the N*(1710). This peak is found where the energies of the pi pi sub-system fall in the region of the sigma-resonance. We do not find evidence for the Roper resonance in our study indicating a more complex structure for this resonance, nor for any state with total isospin I = 3/2 or 5/2.
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  • [AIP PARTICLES AND NUCLEI: Seventeenth Internatinal Conference on Particles and Nuclei - Santa Fe, New Mexico (USA) (23-30 October 2005)] AIP Conference Proceedings - On the nature of the Λ(1405) as a superposition of two states

    Oset, E.  

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  • N* production from pp and (p)over-barp collisions

    Wu, Jia-Jun   Cao, Xu   Molina, R.   Oset, E.   Zou, B. S.  

    With an effective Lagrangian approach, we give a full analysis on the NN -> NN pi pi and pp -> pn pi(+) reactions for proton beam energy from 1 to 1.5 GeV. The results are very consistent with the experiment data from CELSIUS, KEK, COSY, and so on. Based on these results, we consider the (N) over barN -> (N) over barN pi pi and (p) over barp -> (p) over barn pi(+) for proton beam energy up to 4 GeV. Compare to the pp collisions, there are many benefits to study N* resonances in these two reactions. And for the high proton beam energy up to 15 GeV, we consider some new resonances with hidden charm which are definitely beyond three constituent quarks model in the (p) over barp -> (p) over bar pJ/psi and (p) over barp -> (p) over barp eta(c), where there are very nice places to find these new N*(c (c) over bar). The predicted results about (p) over tildep collisions can be looked for at the forthcoming PANDA/FAIR experiments.
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  • The Y(3940), Z(3930) and the X(4160) as dynamically generated resonances from the vector-vector interaction

    Molina, R.   Oset, E.  

    We apply a unitary approach together with a set of hidden-gauge Lagrangians to study the vector-vector interaction. Concretely, we focus on the sector with quantum numbers charm C - 0 and strangeness S - 0 in the region around 4000 MeV. We get five poles, three of which could be identified with the Y(3940), Z(3930) and X(4160). These poles appear with quantum numbers I = 0 and J(PC) = 0(++), 2(++) and 2(++), respectively, and can be considered as hadronic molecules made of D*(D) over bar*, D*(s)(D) over bar*(s), decaying to a pair of light vectors, light-heavy vector or pseudoscalar-pseudoscalar.
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  • Critical view of the claimed Theta(+) pentaquark

    Oset, E.   Martinez Torres, A.  

    We use a theoretical model of the gamma d -> K(+)K(-) n p reaction adapted to the experiment done at LEPS where a peak was observed and associated to the Theta(+)(1540) pentaquark. The study shows that the method used in the experiment to associate momenta to the undetected proton and neutron, together with the chosen cuts, necessarily creates an artificial broad peak in the assumed K(+)n invariant mass in the region of the claimed Theta(+)(1540). It is shown that the LEPS fit to the data, used to make the claim of the Theta(+)(1540), grossly distorts the background. An alternative fit, assuming a background plus a fluctuation, returns a background practically equal to the theoretical one and a fluctuation identical to the one seen in the experimental K(-)p spectrum of 2 sigma significance.
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  • Photoproduction of the f(2)(1270) resonance

    Xie, Ju-Jun   Oset, E.  

    We have performed a calculation of the gamma(p) -> pi(+) p-p reaction, where the two pions have been separated in D-wave producing the f(2)(1270) resonance. We use elements of the local hidden gauge approach that provides the interaction of vector mesons in which the f(2)(1270) resonance appears as rho-rho. molecular state in L =3D 0 and spin 2. The vector meson dominance, incorporated in the local hidden gauge approach converts a photon into a rho(0) meson and the other meson connects the photon with the proton. The picture is simple and has no free parameters, since the parameters of the theory have been constrained in the previous study of the vector-vector states. In a second step we introduce new elements, not present in the local hidden gauge approach, adapting the rho propagator to Regge phenomenology and introducing the rho NN tensor coupling. We find that both the differential cross section as well as the t dependence of the cross section are in good agreement with the experimental results and provide support for the molecular picture of the f(2)(1270) resonance in the first baryonic reaction where it has been tested.
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  • The role of vector-baryon channels and resonances in the gamma p -> K-0 Sigma(+) and gamma n -> K-0 Sigma(0) reactions near the K*Lambda threshold

    Ramos, A.   Oset, E.  

    We have studied the gamma p -> K-0 Sigma(+) reaction in the energy region around the K*Lambda and K*Sigma 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*Lambda and K*Sigma 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 properties. We also show results for the complementary gamma n -> K-0 Sigma(0) reaction, the measurement of which would test the mechanism proposed in this work. (C) 2013 Elsevier B.V. All rights reserved.
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  • $\tau^{-}\rightarrow \nu_{\tau} M_{1}M_{2}$ τ - → ν τ M 1 M 2 , with M1, M2 pseudoscalar or vector mesons

    Dai, L. R.   Pavao, R.   Sakai, S.   Oset, E.  

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  • Axial resonances in the open and hidden charm sectors

    Gamermann, D.   Oset, E.  

    A SU(4) flavor symmetrical Lagrangian is constructed for the interaction of the pseudo-scalar mesons with the vector mesons. SU(4) symmetry is broken to SU(3) by suppression of terms in the Lagrangian where the interaction should be driven by charmed mesons. Chiral symmetry can be restored by setting this new SU(4) symmetry-breaking parameters to zero. Unitarization in coupled channels leads to the dynamical generation of resonances. Many known axial resonances can be identified including the new controversial X(3872) and the structure found recently by Belle around 3875MeV in the hidden charm sector. Also new resonances are predicted, some of them with exotic quantum numbers.
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  • [AIP SCALAR MESONS: An Interesting Puzzle for QCD - Utica, New York (USA) (16-18 May, 2003)] AIP Conference Proceedings - Chiral Dynamics of Scalar Mesons: Radiative φ Decay and σ in the Medium through π0π0 Nuclear Photoproduction

    Oset, E.  

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  • A new perspective on the Faddeev equations and the (K)over-bar N N system from chiral dynamics and unitarity in coupled channels

    Oset, E.   Jido, D.   Sekihara, T.   Torres, A. Martinez   Khemchandani, K. P.   Bayar, M.   Yamagata-Sekihara, J.  

    We review recent work concerning the (K) over bar N interaction and Faddeev equations with chiral dynamics which allow us to look at the (K) over bar N N from a different perspective and pay attention to problems that have been posed in previous studies on the subject. We then show results which provide extra experimental evidence on the existence of two Lambda(1405) states. Then show the findings of a recent approach to Faddeev equations using chiral unitary dynamics, where an explicit cancellation of the two-body off-shell amplitude with three-body forces stemming from the same chiral Lagrangians takes place. This removal of the unphysical off-shell part of the amplitudes is most welcome and renders the approach unambiguous, showing that only on-shell two-body amplitudes need to be used. With this information in mind we use an approximation to the Faddeev equations within the fixed center approximation to study the (K) over bar N N system, providing answers within this approximation to questions that have been brought before and evaluating binding energies and widths of this three-body system. As a novelty with respect to recent work on the topic we find a bound state of the system with spin S = 1 like a bound state of (K) over bar -deuteron, less bound that the one of S = 0, where all recent efforts have been devoted. The width is relatively large in this case, suggesting problems in a possible experimental observation. (C) 2012 Elsevier B.V. All rights reserved.
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  • The antikaon-nucleus interaction and alternative views to deeply bound antikaonic nuclear systems

    Ramos, A.   Magas, V. K.   Oset, E.   Toki, H.  

    We present an overview of the latest theoretical studies on the antikaon properties in the nuclear medium, in connection with the recent experimental claims of very deeply bound antikaon nuclear states. We argue that proper many-body formulations using modern realistic antikaon-nucleon interactions are not able to generate such systems. Instead, a simple two-nucleon antikaon absorption mechanism where the remaining nucleus acts as spectator explains the enhancement observed in semi-inclusive proton momentum spectra, seen as a bump in the KEK PS-E549 experiment on a He-4 target or as a peak in the FINUDA experiment on a Li-6 target. This signal is clearly visible in another FINUDA experiment measuring the invariant mass of A-proton pairs after two-nucleon kaon absorption. We also show that another peak of this experiment, seen at lower invariant masses and interpreted as a bound K-pp state, is simply generated by the same two-nucleon absorption mechanism followed by final-state interactions of the produced particles with the residual nucleus. Our conclusion is that all the experimental claims for the formation of very deeply bound antikaonic nuclear systems receive an alternative explanation in terms of conventional nuclear processes. (c) 2008 Elsevier B.V. All rights reserved.
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  • Dynamically generated resonances from the vector octet-baryon octet interaction

    Oset, E.   Ramos, A.  

    We study the interaction of vector mesons with the octet of stable baryons in the framework of the local hidden gauge formalism using a coupled-channels unitary approach. We examine the scattering amplitudes and their poles, which can be associated to known J(P) = 1/2(-), 3/2(-) baryon resonances, in some cases, or give predictions in other ones. The formalism employed produces doublets of degenerate J(P) = 1/2(-), 3/2(-) states, a pattern which is observed experimentally in several cases. The findings of this work should also be useful to guide present experimental programs searching for new resonances, in particular in the strange sector where the current information is very poor.
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  • The role of the Lambda(1405) in the pp -> pK(+)Lambda(1405) reaction RID C-6441-2009

    Geng, L. S.   Oset, E.  

    We report a theoretical study of the pp -> pK(+)Lambda(1405) reaction, which was recently investigated at COSY-Julich 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 Lambda(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.
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