arXiv subjects

A. Feijoo

Publications and source records attributed to A. Feijoo.

26 records · Page 2Linked to original sources

arXiv2020

The molecular nature of some exotic hadrons

The exciting discovery by LHCb of the $P_c(4312)^+$ and $P_c(4450)^+$ pentaquarks, or the suggestion of a tetraquark nature for the $Z_c(3900)$ state seen at BESIII and Belle, have triggered a lot of activity in the field of hadron physics, with new experiments planned for searching other exotic mesons and baryons, and many theoretical developments trying to disentangle the true multiquark nature from their possible molecular origin. After a brief review of the present status of these searches, this paper focusses on recently seen or yet to be discovered exotic heavy baryons that may emerge from a conveniently unitarized meson-baryon interaction model in coupled channels. In particular, we will show how interferences between the different coupled-channel amplitudes of the model may reveal the existence of a $N^*$ resonance around 2 GeV having a meson-baryon quasi-bound state nature. We also discuss the possible interpretation of some of the $Ω_c$ states recently discovered at LHCb as being hadron molecules. The model also predicts the existence of doubly-charmed quasibound meson-baryon $Ξ_{cc}$ states, which would be excited states of the ground-state $Ξ_{cc}(3621)$ MeV, whose mass has only been recently established. Extensions of these results to the bottom sector will also be presented.

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arXiv2016

The chiral S=-1 meson-baryon interaction with new constrains on the NLO contributions

We present a study of the $S=-1$ meson-baryon interaction, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the model have been fitted to a large set of experimental scattering data in different two-body channels, to threshold branching ratios, and to the precise SIDDHARTA value of the energy shift and width of kaonic hidrogen. In contrast to other groups, we have taken into consideration the $K^- p\to K^+Ξ^-, K^0Ξ^0$ reaction data, since we found in a previous work to be especially sensitive to the NLO parameters of the chiral Lagrangian. In the present work we also include the Born terms, which usually have very little effect, and find them to be non-negligible in the $K^- p\to KΞ$ channels, correspondingly causing significant modifications to the NLO parameters. We furthermore show that the importance of the Born terms becomes more visible in the isospin projected amplitudes of the $K^-p \to KΞ$ reactions. The measurement of processes that filter single isospin components, like the $K^0_L p \to K^+ Ξ^0$ reaction that could be measured at the proposed secondary $K^0_L$ beam at Jlab, would put valuable constraints on the chiral models describing the meson-baryon interaction in the $S=-1$ sector.

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arXiv2016

A hidden-charm $S=-1$ pentaquark from the decay of $Λ_b$ into $J/ψηΛ$

The hidden charm pentaquark state $P_c(4450)$ 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 $S=-1$ sector. In this work we argue that a hidden-charm strange pentaquark could be seen from the decay of the $Λ_b$, just as in the case of the non-strange $P_c(4450)$, but looking into the $J/ψηΛ$ decay mode and forming the invariant mass spectrum of $J/ψΛ$ 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 $J/ψηΛ$ final states to be populated with similar strength as the $J/ψK^- p$ states employed for the observation of the non-strange pentaquark. This makes the $Λ_ b \to J/ψηΛ$ decay to be an interesting process to observe a possible strange partner of the $P_c(4450)$ . We study the dependence of the $J/ψΛ$ mass spectra on various model ingredients and on the unknown properties of the strange pentaquark.

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arXiv2016

Workshop on Physics with Neutral Kaon Beam at JLab (KL2016) Mini-Proceedings

The KL2016 Workshop is following the Letter of Intent LoI12-15-001 "Physics Opportunities with Secondary KL beam at JLab" submitted to PAC43 with the main focus on the physics of excited hyperons produced by the Kaon beam on unpolarized and polarized targets with GlueX setup in Hall D. Such studies will broaden a physics program of hadron spectroscopy extending it to the strange sector. The Workshop was organized to get a feedback from the community to strengthen physics motivation of the LoI and prepare a full proposal. Further details about the Workshop can be found on the web page of the conference: http://www.jlab.org/conferences/kl2016/index.html .

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arXiv2015

The $Λ_b \to J/ψ~ K ~ Ξ$ decay and the higher order chiral terms of the meson baryon interaction

We study the weak decay of the $Λ_b$ into $ J/ψ~ K ~ Ξ$ and $J/ψ~ η~ Λ$ states, and relate these processes to the $Λ_b \to J/ψ~ \bar K ~N$ decay mode. The elementary weak transition at the quark level proceeds via the creation of a $J/ψ$ meson and an excited $sud$ system with $I=0$, which upon hadronization leads to $\bar K N$ or $ηΛ$ pairs. These states undergo final state interaction in coupled channels and produce a final meson-baryon pair. The $K Ξ$ state only occurs via rescattering, hence making the $Λ_b \to J/ψ~ K ~ Ξ$ process very sensitive to the details of the meson-baryon interaction in strangeness $S=-1$ and isospin $I=0$. We show that the corresponding invariant mass distribution is dominated by the next-to-leading order terms of the chiral interaction. The $I=0$ selectivity of this decay, and its large sensitivity to the higher order terms, makes its measurement very useful and complementary to the $K^- p \to K Ξ$ cross section data. The rates of the $Λ_b \to J/ψ~ K ~ Ξ$ and $Λ_b \to J/ψ~ η~ Λ$ invariant mass distributions are sizable compared to those of the $Λ_b \to J/ψ~ \bar K ~N$ decay, which is measured experimentally, thus, we provide arguments for an experimental determination of these decay modes that will help us understand better the chiral dynamics at higher energies.

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arXiv2015

The $\bar{K} N \rightarrow K Ξ$ reaction in coupled channel chiral models up to next-to-leading order

The meson-baryon interaction in s-wave in the strangeness S=-1 sector has been studied, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the Lagrangian have been fitted to a large set of experimental data in different two-body channels, paying special attention to the $\bar{K} N \rightarrow K Ξ$ reaction, which is particularly sensitive to the NLO terms. With the aim of improving the model in the $KΞ$ production channels, effects of the high spin hyperon resonances $Σ(2030)$ and $Σ(2250)$ have been taken into account phenomenologically.

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arXiv2014

The $\bar{K} N \rightarrow K Ξ$ reaction in coupled channel chiral models up to next-to-leading order

We study the meson-baryon interaction in S-wave in the strangeness S=-1 sector using a chiral unitary approach based on a next-to-leading order chiral SU(3) Lagrangian. We fit our model to the large set of experimental data in different two-body channels. We pay particular attention to the $\bar{K} N \rightarrow K Ξ$ reaction, where the effect of the next-to-leading order terms in the Lagrangian are sufficiently large to be observed, since at tree level the cross section of this reaction is zero. For these channels we improve our approach by phenomenologically taking into account effects of the high spin hyperonic resonances.

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arXiv2013

Effects of the next-to-leading order terms in the chiral SU(3) Lagrangian on the strangeness -1 s-wave meson-baryon interactions

The meson-baryon interactions in s-wave in the strangeness S=-1 sector are studied using a chiral unitarity approach based on the next-to-leading order chiral SU(3) Lagrangian. The model is fitted to the large set of experimental data in different two-body channels. Particular attention is paid to the $Ξ$ hyperon production reaction, $\bar{K} N \rightarrow K Ξ$, where the effect of the next-to-leading order terms in the Lagrangian play a crucial role, since the cross section of this reaction at tree level is zero.

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