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Now showing items 49 - 64 of 187

  • A hidden-charm S =3D-1 pentaquark from the decay Lambda(b) into J/psi eta Lambda states

    Feijoo, A.   Magas, V. K.   Ramos, A.   Oset, E.  

    The hidden-charm pentaquark P-c(4450) observed recently by the LHCb collaboration may be of molecular nature, as advocated by some unitary approaches that also predict pentaquark partners in the strangeness S =3D -1 sector. In this work we argue that a hidden-charm strange pentaquark could be seen from the decay of the Lambda b, just as in the case of the non-strange P-c(4450), but looking into the J/psi eta Lambda decay mode and forming the invariant mass spectrum of J/psi Lambda pairs. In the model presented here, which assumes a standard weak decay topology and incorporates the hadronization process and final-state interaction effects, we find the J/psi eta Lambda final states to be populated with similar strength as the J/psi K- p states employed for the observation of the non-strange pentaquark. This makes the Lambda b -> J/psi eta Lambda decay to be an interesting process to observe a possible strange partner of the P-c(4450). We study the dependence of the J/psi Lambda mass spectra on various model ingredients and on the unknown properties of the strange pentaquark.
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  • f(1)(1285) decays into a(0)(980) pi(0),f(0)(980) pi(0) and isospin breaking

    Aceti, F.   Dias, J. M.   Oset, E.  

    We evaluate the decay width for the processes f1(1285). p 0 a0(980) and f1(1285). p 0 f0(980) taking into account that all three resonances are dynamically generated from the meson- meson interaction, the f1(1285) from K* _ K - c. c. and the a0(980), f0(980) from p., K _ K and pp, K _ K, respectively. We use a triangular mechanism similar to that of.(1405). pp., which provides a decay width for f1(1285). p 0 a0(980) with a branching fraction of the order of 30%, in agreement with experiment. At the same time we evaluate the decay width for the isospin- forbidden f1(1285). p 0 f0(980), which appears when we consider different masses for the charged and neutral kaons, and show that it is much more suppressed than in the.(1405). pp. case, but gives rise to a narrow shape of the p + p- distribution similar to the one found in the eta(1405) -> pi pi eta decay.
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  • Predictions for the Lambda(b) -> J/psi Lambda (1405) decay

    Roca, L.   Mai, M.   Oset, E.   Meissner, Ulf-G.  

    We calculate the shape of the pi Sigma and (K) over bar N invariant mass distributions in the Lambda(b) -> J/psi pi Sigma and Lambda(b) -> J/psi (K) over bar N decays that are dominated by the Lambda (1405) resonance. The weak interaction part is the same for both processes and the hadronization into the different meson-baryon channels in the final state is given by symmetry arguments. The most important feature is the implementation of the meson-baryon final-state interaction using two chiral unitary models from different theoretical groups. Both approaches give a good description of antikaon-nucleon scattering data, the complex energy shift in kaonic hydrogen and the line shapes of pi Sigma K in photoproduction, based on the two-pole scenario for the Lambda (1405). We find that this reaction reflects more the higher mass pole and we make predictions of the line shapes and relative strength of the meson-baryon distributions in the final state.
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  • Helicity amplitudes of the Lambda(1670) and two Lambda(1405) as dynamically generated resonances

    Doering, M.   Jido, D.   Oset, E.  

    We determine the helicity amplitudes A(1/2) and radiative decay widths in the transition Lambda(1670) -> gamma Y (Y = Lambda or Sigma(0)). The Lambda(1670) is treated as a dynamically generated resonance in meson-baryon chiral dynamics. We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 2 +/- 1 keV and to -gamma Sigma(0) as 120 +/- 50 keV. Also, the Q(2)-dependence of the helicity amplitudes A(1/2) is calculated. We find that the K Xi component in the Lambda(1670) structure, mainly responsible for the dynamical generation of this resonance, is also responsible for the significant suppression of the decay ratio Gamma(gamma A)/Gamma(gamma Sigma 0). A measurement of the ratio would, thus, provide direct access to the nature of the Lambda(1670). To compare the result for the Lambda(1670), we calculate the helicity amplitudes Lambda(1/2) for the two states of the Lambda(1405). Also, the analytic continuation of Feynman parameterized integrals of more complicated loop amplitudes to the complex plane is developed which allows for an internally consistent evaluation of A(1/2).
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  • rho rho N and rho rho Delta molecules with J(P)=5/2(+) and J(P)=7/2(+)

    Sun, Bao-Xi   Chen, Hua-Xing   Oset, E.  

    The rho rho N and rho rho Delta three-body systems have been studied within the framework of the fixed center approximation of Faddeev equation. The rho rho interaction in isospin I = 0, spin S = 2 is strongly attractive, and so are the N rho, Delta rho interactions. This leads to bound states of both rho rho N and rho rho Delta. We find peaks of the modulus squared of the scattering matrix around 2227 MeV for rho rho N, and 2372 MeV for rho rho Delta. Yet, the strength of the peak for the rho rho N amplitude is much smaller than for rho rho Delta, weakening the case for a rho rho N bound state, or a dominant rho rho N component. A discussion is made on how these states can be searched for in present programs looking for multimeson final states in different reactions.
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  • Triangle singularities in B- -> K-pi D--(s0)+ and B- -> K-pi D--(s1)+

    Sakai, S.   Oset, E.   Ramos, A.  

    We study the appearance of structures in the decay of the B- into K-pi D--(s0)+ (2317) and K-pi D--(s1)+ (2460) final states by forming invariant mass distributions of pi D--(s0)+ and pi D--(s1)+ pairs, respectively. The structure in the distribution is associated to the kinematical triangle singularity that appears when the B- -> K- K*(0) D-0 (B- -> K- K*(0) D*(0)) decay process is followed by the decay of the K*(0) into pi(-) K+ and the subsequent rescattering of the K+ D-0 (K+ D*(0)) pair forming the D-s0(+) (2317) (D-s1(+) (2460)) resonance. We find this type of non-resonant peaks at 2850MeV in the invariant mass of pi D--(s0) pairs from B- -> K- pi(-) D-s0(+) (2317) decays and around 3000MeV in the invariant mass of pi D--(s1)+ pairs from B- -> K- pi(-) D-s1(+)(2460) decays. By employing the measured branching ratios of the B- -> K- K*(0) D-0 and B- -> K- K*(0) D*(0) decays, we predict the branching ratios for the processes B- into K-pi D--(s0)+ (2317) K-pi D--(s1)+ (2460), in the vicinity of the triangle singularity peak, to be about 8 x 10(-6) and 1 x 10(-6), respectively. The observation of this reaction would also give extra support to the molecular picture of the D-s0(+)(2317) and D-s1(+)(2460).
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  • Coupled channels dynamics in the generation of the Omega (2012) resonance

    Pavao, R.   Oset, E.  

    We look into the newly observed Omega (2012) state from the molecular perspective in which the resonance is generated from the (K) over bar Xi*, eta Omega and (K) over bar Xi channels. We find that this picture provides a natural explanation of the properties of the Omega (2012) state. We stress that the molecular nature of the resonance is revealed with a large coupling of the Omega (2012) to the (K) over bar Xi* channel, that can be observed in the Omega (2012) -> (K) over bar pi Xi decay which is incorporated automatically in our chiral unitary approach via the use of the spectral function of Xi* in the evaluation of the (K) over bar Xi* loop function.
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  • Pseudoscalar or vector meson production in non-leptonic decays of heavy hadrons

    Liang, Wei-Hong   Oset, E.  

    We have addressed the study of non-leptonic weak decays of heavy hadrons (Lambda b, Lambda c, B and D), with external and internal emission to give two final hadrons, taking into account the spin-angular momentum structure of the mesons and baryons produced. A detailed angular momentum formulation is developed which leads to easy final formulas. By means of them we have made predictions for a large amount of reactions, up to a global factor, common tomany of them, that we take from some particular data. Comparing the theoretical predictions with the experimental data, the agreement found is quite good in general and the discrepancies should give valuable information on intrinsic form factors, independent of the spin structure studied here. The formulas obtained are also useful in order to evaluate meson-meson or meson-baryon loops, for instance of B decays, in which one has PP, PV, VP or VV intermediate states, with P for pseudoscalar mesons and V for vector meson and lay the grounds for studies of decays into three final particles.
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  • Structure of Lambda(1405) and chiral dynamics

    Jido, D.   Oller, J.A.   Oset, E.   Ramos, A.   Meissner, U.-G.  

    We report on a recent theoretical work on the structure of the Lambda(1405) resonance within a chiral unitary approach, in which the resonance is dynamically generated in meson-baryon scattering. Studying the analytic structure of the scattering amplitude, we have found that there are two poles lying around energies of Lambda(1405) with different widths and couplings to the meson-baryon states. We discuss reactions to conform the double pole structure in experiment and elastic K-p scattering at low energies. [All rights reserved Elsevier]
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  • Baryon Resonances

    Oset, E.   Sarkar, S.   Sun, Bao Xi   Vacas, M. J. Vicente   Ramos, A.   Gonzalez, P.   Vijande, J.   Torres, A. Martinez   Khemchandani, K.  

    In this talk I show recent results on how many excited baryon resonances appear as systems of one meson and one baryon, or two mesons and one baryon, with the mesons being either pseudoscalar or vectors. Connection with experiment is made including a discussion on old predictions and recent results for the photoproduction of the Lambda(1405) resonance, as well as the prediction of one 1/2(+) baryon state around 1920 MeV which might have been seen in the gamma p -> K(+)Lambda reaction.
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  • A-dependence of the gamma- and p-induced production of the Lambda(1520) from nuclei

    Kaskulov, M.   Roca, L.   Oset, E.  

    Using results of a recent calculation of the A(1520) in the nuclear medium, which show that the medium width is about five times the free width, we study the A-dependence of the A(1520) production cross-section in the reactions gamma A --> K(+) Lambda(1520)A' and p A --> p K(+) Lambda(1520)A'. We find a sizable A-dependence in the ratio of the nuclear cross-sections for heavy nuclei with respect to a light one due to the large value of the A(1520) width in the medium, showing that devoted experiments, easily within reach in present facilities, can provide good information on that magnitude by measuring the cross-sections studied here.
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  • V P gamma radiative decay of resonances dynamically generated from the vector meson-vector meson interaction

    Yamagata-Sekihara, J.   Oset, E.  

    We evaluate the radiative decay into a vector, a pseudoscalar and a photon of several resonances dynamically generated from the vector-vector interaction. The process proceeds via the decay of one of the vector components into a pseudoscalar and a photon, which have an invariant mass distribution very different from phase space as a consequence of the two vector structure of the resonances. Experimental work along these lines should provide useful information on the nature of these resonances. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.
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  • A Plausible Explanation of the Delta(5/2+)(2000) Puzzle

    Gonzalez, P.   Xie, Ju-Jun   Martinez Torres, A.   Oset, E.  

    From a Faddeev calculation for the pi - (Delta rho)N5/2-(1675) system we propose an alternative interpretation of Delta(5/2+)(2000) (**) as composed of two distinctive resonances, Delta(5/2+)(similar to 1740) and Delta(5/2+)(similar to 2200). This proposal gets further support from the possible assignment of other baryon states found in the I = 1/2; 3/2 sectors with J(P) = 1/2(+); 3/2(+); 5/2(+) to known baryonic resonances. In particular, Delta(1/2+)(1750) (*) is naturally interpreted as a pi N1/2-(1650) bound state.
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  • Disclosing D* (D)over bar* molecular states in the B-c(-) -> pi(-) J/psi omega decay

    Dai, L. R.   Dias, J. M.   Oset, E.  

    We study the B-c(-) -> pi(-) J/omega and B-c(-) -> pi(-) D* (D) over bar* reactions and show that they are related by the presence of two resonances, the X(3940) and X(3930), that are of molecular nature and couple most strongly to D* (D) over bar*, but also to J/psi omega. Because of that, in the J/psi omega mass distribution we find a cusp with large strength at the D* (D) over bar* threshold and predict the ratio of strengths between the peak of the cusp and the maximum of the D* (D) over bar* distribution close to D* (D) over bar* threshold, which are distinct features of the molecular nature of these two resonances.
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  • Photo- and electro-production of mesons on nucleons and nuclei

    Oset, E.   Doering, M.   Strottman, D.   Jido, D.   Napsuciale, M.   Sasaki, K.   Vaquera-Araujo, C. A.   Kaskulov, M.   Hernandez, E.   Nagahiro, H.   Hirenzaki, S.  

    In these lectures I will show some results obtained with the chiral unitary approach applied to the photo- and electro-production of mesons. The results for the photo-production of eta pi(0)p and K(0)pi(0)Sigma(+), together with related reactions will be shown, having with common denominator the excitation of the Delta(1700) resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show the results obtained for the e(+)e(-) -> phi f(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 photo-production of the omega in the nuclei, showing that present experimental results claiming a shift of the omega mass in the medium are tied to a particular choice of background and are not conclusive. On the other hand, the same experimental results show unambiguously a huge increase of the omega width in the nuclear medium. (c) 2007 Elsevier B.V. All fights reserved.
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  • The width of the omega meson in the nuclear medium

    Ramos, A.   Tolos, L.   Molina, R.   Oset, E.  

    We evaluate the width of the omega meson in nuclear matter. We consider the free decay mode of the omega into three pions, which is dominated by rho IEuro decay, and replace the rho and pi propagators by their medium-modified ones. We also take into account the quasielastic and inelastic processes induced by a vector-baryon interaction dominated by vector meson exchange, as well as the contributions coming from the mechanism with medium-modified K , propagators. We obtain a substantial increase of the omega width in the medium, reaching a value of 121 +/- 10 MeV at normal nuclear matter density for an omega at rest, which comes mainly from omega N -> pi pi N, omega NN -> pi NN processes associated to the dominant omega -> rho IEuro decay mode. The value of the width increases moderately with momentum, reaching values of around 200MeV at 600MeV/c.
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