Search

We discuss two complementary strategies to search for light dark matter (LDM) exploiting the positron beam possibly available in the future at Jefferson Laboratory. LDM is a new compelling hypothesis that identifies dark matter with new sub-GeV "hidden sector" states, neutral under standard model interactions and interacting with our world through a new force. Accelerator-based searches at the intensity frontier are uniquely suited to explore it. Thanks to the high intensity and the high energy of the CEBAF (Continuous Electron Beam Accelerator Facility) beam, and relying on a novel LDM production mechanism via positron annihilation on target atomic electrons, the proposed strategies will allow us to explore new regions in the LDM parameters space, thoroughly probing the LDM hypothesis as well as more general hidden sector scenarios., 11 pages, 8 figures. Prepared for submission in EPJA. This work supersedes the corresponding contribution in arXiv:2007.15081. Added aknowledgement to Jefferson Lab

We investigate the hidden-charm pentaquarks as a Λc͞D⁽*⁾ – Σc⁽*⁾͞D⁽*⁾ hadronic molecule coupling to a compact five-quark state. The coupling to the compact state leads to an hadron short-range interaction generating an attraction. In addition, the one pion exchange potential (OPEP) as a long-range interaction is introduced by the Lagrangians satisfying the chiral and heavy quark spin symmetries. The OPEP has been known as a driving force to bind atomic nuclei, where the tensor term leading the coupled-channel effect generates a strong attraction. The mass degeneracy of heavy hadrons due to the heavy quark spin symmetry enhances the OPEP derived by the πD⁽*⁾͞D⁽*⁾ and πΣc⁽*⁾Σc⁽*⁾ couplings. Introducing those interactions, we consistently explain the masses and widths of the Pc states reported by LHCb in 2019. The short range interaction has a dominant role to determine the energy-level structures, while the OPEP tensor term does the decay width., Facultad de Ciencias Exactas

We study the bottomonium spectrum using a relativistic potential model in the momentum space. This model is based on a complete one gluon exchange interaction with a momentum dependent screening factor to account for the effects due to virtual pair creation that appear close to the decay thresholds. The overall model does not make use of nonrelativistic approximations. We fit well established bottomonium states below the open charm threshold and predict the rest of the spectrum up to $\approx 11200$ MeV and $J^{PC}=3^{--}$. Uncertainties are treated rigorously and propagated in full to the parameters of the model using a Monte Carlo to identify if which deviations from experimental data can be absorbed into the statistical uncertainties of the models and which can be related to physics beyond the $b\bar{b}$ picture, guiding future research. We get a good description of the spectrum, in particular the Belle measurement of the $\eta_b(2S)$ state and the $\Upsilon(10860)$ and $\chi_b(3P)$ resonances., Comment: 11 pages, 3 figures, 8 tables

In two recent papers, we used the hadro-quarkonium model to study the properties of hidden-charm and bottom tetraquarks and pentaquarks. Here, we extend the previous results and calculate the masses of heavy-quarkonium-kaon/hyperon systems. We also compute the spectrum of hidden-charm and bottom tetraquarks with strangeness in the compact tetraquark (diquark-antidiquark) model. If heavy-light exotic systems with non-null strangeness content were to be observed experimentally, it might be possible to distinguish among the large variety of available theoretical pictures for tetra- and pentaquark states and, possibly, rule out those which are not compatible with the data. peerReviewed

The observation of five $$\varOmega _c $$Ωc= ssc states by LHCb [Aaij et al. Phys. Rev. Lett. 118, 182001 (2017)] and the confirmation of four of them by Belle [Yelton et al. Phys. Rev. D 97, 051102 (2018)], may represent an important milestone in our understanding of the quark organization inside hadrons. By providing results for the spectrum of $$\varOmega _{ c}$$Ωc baryons and predictions for their $$\varXi _{ c}^{+}K^{-}$$Ξc+K- and $$\varXi _{ c}'^{+}K^{-}$$Ξc′+K- decay amplitudes within an harmonic oscillator based model, we suggest a possible solution to the $$\varOmega _{c}$$Ωc quantum number puzzle and we extend our mass and decay width predictions to the $$\varOmega _b$$Ωb states. Finally, we discuss why the set of $$\varOmega _{ c(b)}$$Ωc(b) baryons is the most suitable environment to test the validity of three-quark and quark–diquark effective degrees of freedom.

We describe the relativistic interacting quark-diquark model formalism and its application to the calculation of strange and nonstrange baryon spectra. The results are compared to the existing experimental data. We also discuss the application of the model to the calculation of other baryon observables, like baryon magnetic moments, open-flavor strong decays and baryon masses with self-energy corrections.

We present an unquenched quark model calculation of the mass shifts of ground-state octet and decuplet baryons due to the coupling to the meson-baryon continuum. All ground-state baryons and pseudoscalar mesons are included in our calculation as intermediate states. The $q\bar{q}$ pair creation effects are taken explicitly into account through a microscopic, QCD-inspired, quark-antiquark pair creation mechanism.

The relativistic interacting quark-diquark model of baryons, recently developed, is here extended to introduce a spin-isospin transition interaction into the mass operator. The refined version of the model is used to calculate the non strange baryon spectrum. The results are compared to the present experimental data.

The physical meaning of bare and dressed scattering matrix singularities has been investigated. Special attention has been attributed to the role of well known invariance of scattering matrix with respect to the field transformation of the effective Lagrangian. Examples of evaluating bare and dressed quantities in various models are given.

The formalism for a new generation of unquenched quark models for baryons in which the effects of quark–antiquark pairs are taken into account in an explicit form via a microscopic, QCD-inspired, quark–antiquark creation mechanism, is presented. As an application the quark–antiquark contribution to the spin of the proton and the Σ+ is discussed. Finally the strangeness radius of the Σ+ in the closure limit is calculated.

The formalism for a new generation of unquenched quark models for baryons is presented. The effects of quark-antiquark pairs are taken into account in an explicit form via a microscopic, QCD-inspired, quark-antiquark creation mechanism. As an application, the quark-antiquark contribution to the spin of the proton is discussed.

We perform a calculation of the relativistic transition form factors for the electromagnetic excitation of the nucleon resonances. We use as input the 3-quark wave functions obtained in a Constituent Quark Model with three-body forces in the hypercentral approach. With respect to the non relativistic calculations a significant contribution is obtained up to Q2≃ 2 (GeV/c)2. However, the low Q2-behaviour exhibits a lack of strength, which may be connected with the need of taking into account explicitly further degrees of freedom beyond the three constituent quark ones.

We construct a simple 3-body quark model for the non strange nucleon resonances and we give results for the spectrum, the helicity amplitudes and the transition form factors. All the observables, in particular the transition form factors, are evaluated analytically and the results are compared with those of other models.