No abstract

Different experiments on hadron spectroscopy have long suspected the existence of several cascade states in the 1900 − 2000 MeV region. They are usually labeled under the common name of Ξ(1950). As we argue here, there are also theoretical reasons supporting the idea of several Ξ(1950) resonances. In particular, we propose the existence of three Ξ(1950) states: one of these states would be part of a spin-parity 1 2 − decuplet and the other two probably would belong to the 5 2 + and 5 2 − octets. We also identify which decay channels are the more appropriate for the detection of each of the previous states.PACS 11.30.Hv, 11.30 . Among the latter resonances, the chiral structure and spin parity of two of them, Ξ(1690) and Ξ(1820), seem to be theoretically understood [2-6] 1 . The other two three star cascade resonances quoted in the PDG are the Ξ(1950) and Ξ (2030) states, which spin-parity have not been determined yet. Here we will focus in these two states, in particular in the Ξ(1950) resonance.The Ξ(1950) resonance was discovered in 1965 by Badier et al. [8] in the decay channels The authors of Ref. [9] theorized that this resonance may complete the (1775) The possibility that there may be several cascade resonances in the 1900 − 2000 MeV region was first suggested by Briefel et al. [11] who noticed that different values for the Ξ(1950) mass were to be found in different decay channels. This expectation has been commonly discussed in later experimental searches. Indeed, Biagi et al. [16] commented that several bubble chamber experiments have seen indications of a rather broad signal in this region but in general the statistical significance is low and it is not clear if they are all observing the same resonance.There are also theoretical/phenomenological reasons to suspect for the existence of several cascade states in the vicinity of 1950 MeV. SU(3)-flavor symmetry was proposed by and Ne'eman [19] as an ordering principle for hadron spectroscopy [20]. This symmetry allows to classify baryons and mesons into multiplets of particles with the same spin and parity. Two consequences of SU(3)-flavor symmetry are the Gell-MannOkubo (GMO) mass relation [18,21], and the correlation between the decay widths of the different hadrons conforming a multiplet. Here we will use the GMO mass relation to identify possible cascade resonances with masses not far from M = 1950 MeV and then try to match the predicted decay widths, assuming the Ξ(1950) belongs to a particular multiplet, to the scarce experimental information available.The GMO mass relation [18,21] relates the masses of the baryons composing a particular multiplet. For the octet case we have 2 (m N + m Ξ ) = 3m Λ + m Σ , while for the decuplets the GMO relation predicts m Ω − m Ξ =

We investigate the Λ(1520) photo-production in the γp → K + Λ(1520) reaction within the effective Lagrangian method near threshold. In addition to the "background" contributions from the contact, t−channel K exchange, and s−channel nucleon pole terms, which were already considered in previous works, the contribution from the nucleon resonance N * (2080) (spin-parity J P = 3/2 − ) is also considered. We show that the inclusion of the nucleon resonance N * (2080) leads to a fairly good description of the new LEPS differential cross section data, and that these measurements can be used to determine some of the properties of this latter resonance. However, serious discrepancies appear when the predictions of the model are compared to the photon-beam asymmetry also measured by the LEPS Collaboration.PACS numbers: 13.75.Cs.; 14.20.-c.; 13.60.Rj.

Approximate heavy-quark spin and flavor symmetry and chiral symmetry play an important role in our understanding of the nonperturbative regime of strong interactions. In this work, utilizing the unitarized chiral perturbation theory, we explore the consequences of these symmetries in the description of the interactions between the ground-state singly charmed (bottom) baryons and the pseudo-Nambu-Goldstone bosons. In particular, at leading order in the chiral expansion, by fixing the only parameter in the theory to reproduce the Λ b (5912) [Λ * b (5920)] or the Λ c (2595) [Λ * c (2625)], we predict a number of dynamically generated states, which are contrasted with those of other approaches and available experimental data. In anticipation of future lattice QCD simulations, we calculate the corresponding scattering lengths and compare them to the existing predictions from a O(p 3 ) chiral perturbation theory study. In addition, we estimate the effects of the next-to-leading-order potentials by adopting heavy-meson Lagrangians and fixing the relevant low-energy constants using either symmetry or naturalness arguments. It is shown that higher-order potentials play a relatively important role in many channels, indicating that further studies are needed once more experimental or lattice QCD data become available.In recent years, heavy-flavor hadron physics has yielded many surprising results and attracted a lot of attention due to intensive worldwide experimental activities, such as BABAR [1], Belle [2, 3], CLEO [4], BES [5], LHCb [6], and CDF [7]. The discoveries and confirmations of the many XY Z particles have established the existence of exotic mesons made of four quarks, such as the Z c (3900) [8,9] and the Z(4430) [10,11], and aroused great interest in the theoretical and lattice QCD community to understand their nature, though no consensus has been reached yet (see, e.g.,Ref.[12]).Different from the case of heavy-meson states, no similar exotic states have been firmly established in the heavy-flavor baryon sector, partly due to the fact that their production is more difficult. Up to now, there have only been a few experimental observations of excited charmed and bottom baryons (see Ref. [13] for a recent and comprehensive review). In the bottom baryon sector, the LHCb Collaboration has reported two excited Λ b states, the Λ b (5912) and the Λ b (5920) [14], with the latter being recently confirmed by the CDF Collaboration [15]. In the charmed baryon sector, a number of excited states have been confirmed by various experiments, including the Λ c (2595), the Ξ c (2790), the Λ c (2625), and the Ξ c (2815) [16]. The spin parities of the first two states and the last two states are assumed to be 1/2 − and 3/2 − , respectively, according to quark model predictions.The conventional picture is that these states are the orbital excitations of the corresponding ground states. There are, however, different interpretations; namely, they are dynamically generated states from the interactions between the ground-state charmed ...

Heavy-quark symmetry as applied to heavy hadron systems implies that their interactions are independent of their heavy-quark spin (heavy-quark spin symmetry) and heavy flavour contents (heavy flavour symmetry). In the molecular hypothesis the X(3872) resonance is a 1 ++ D * D bound state. If this is the case, the application of heavy-quark symmetry to a molecular X(3872) suggests the existence of a series of partner states, the most obvious of which is a possible 2 ++ D * D * bound state for which the two-body potential is identical to that of the 1 ++ D * D system, the reason being that these two heavy hadron-antihadron states have identical light-spin content. As already discussed in the literature this leads to the prediction of a partner state at 4012 MeV, at least in the absence of other dynamical effects which might affect the location of this molecule. However the prediction of further heavy-quark symmetry partners cannot be done solely on the basis of symmetry and requires additional information. We propose to use the one boson exchange model to fill this gap, in which case we will be able to predict or discard the existence of other partner states. Besides the isoscalar 2 ++ D * D * bound state, we correctly reproduce the location and quantum numbers of the isovector hidden-bottom Z b (10610) and Z b (10650) molecular candidates. We also predict the hidden-bottom 1 ++ B * B * and 2 ++ B * B * partners of the X(3872), in agreement with previous theoretical speculations, plus a series of other states. The isoscalar, doubly charmed 1 + DD * and D * D * molecules and their doubly bottomed counterparts are likely to bind, providing a few instances of explicitly exotic systems.2 −D * Σ * c state. Yet, with the exception of the doubly charmed pentaquark family, heavyquark symmetry alone is in general not able to determine the

In this paper, we present a review of recent works on weak decay of heavy mesons and baryons with two mesons, or a meson and a baryon, interacting strongly in the final state. The aim is to learn about the interaction of hadrons and how some particular resonances are produced in the reactions. It is shown that these reactions have peculiar features and act as filters for some quantum numbers which allow to identify easily some resonances and learn about their nature. The combination of basic elements of the weak interaction with the framework of the chiral unitary approach allow for an interpretation of results of many reactions and add a novel information to different aspects of the hadron interaction and the properties of dynamically generated resonances.