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Elena Santopinto

Publications and source records attributed to Elena Santopinto.

31 records · Page 2Linked to original sources
arXiv2016

Can sea quark asymmetry shed light on the orbital angular momentum of the proton?

A striking prediction of several extensions of the constituent quark model, including the unquenched quark model, the pion cloud model and the chiral quark model, is a proportionality relationship between the quark sea asymmetry and the orbital angular momentum of the proton. We investigate to which extent a relationship of this kind is corroborated by the experiment, through a systematic comparison between expectations based on models and predictions obtained from a global analysis of hard-scattering data in perturbative Quantum Chromodynamics. We find that the data allows the angular momentum of the proton to be proportional to its sea asymmetry, though with a rather large range of the optimal values of the proportionality coefficient. Typical values do not enable us to discriminate among expectations based on different models. In order to make our comparison conclusive, the extrapolation uncertainties on the proportionality coefficient should be reduced, hopefully by means of accurate measurements in the region of small proton momentum fractions, where the data is currently lacking. Nevertheless, the unquenched quark model predicts that quarks account for a proton spin fraction much larger than that accepted by the conventional wisdom. We explicitly demonstrate that such a discrepancy can be reabsorbed in the unknown extrapolation region, without affecting the description of current data, by imposing the unquenched quark model expectation as a boundary condition in the analysis of the data itself. We delineate how the experimental programs at current and future facilities may shed light on the region of small momentum fractions.

hep-ph↗
arXiv2016

Hidden-charm pentaquarks as a meson-baryon molecule with coupled channels for $\bar{D}^{(\ast)}Λ_{\rm c}$ and $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$

The recent observation of two hidden-charm pentaquark states by LHCb collaborations prompted us to investigate the exotic states close to the $\bar{D}Λ_{\rm c}$, $\bar{D}^{\ast}Λ_{\rm c}$, $\bar{D}Σ_{\rm c}$, $\bar{D}Σ^{\ast}_{\rm c}$, $\bar{D}^{\ast}Σ_{\rm c}$ and $\bar{D}^{\ast}Σ^{\ast}_{\rm c}$ thresholds. We therefore studied the hadronic molecules that form the coupled-channel system of $\bar{D}^{(\ast)}Λ_{\rm c}$ and $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$. As the heavy quark spin symmetry manifests the mass degenerations of $\bar{D}$ and $\bar{D}^\ast$ mesons, and of $Σ_{\rm c}$ and $Σ^\ast_{\rm c}$ baryons, the coupled channels of $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ are important in these molecules. In addition, we consider the coupling to the $\bar{D}^{(\ast)}Λ_{\rm c}$ channel whose thresholds are near the $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ thresholds, and the coupling to the state with nonzero orbital angular momentum mixed by the tensor force. This full coupled channel analysis of $\bar{D}^{(\ast)}Λ_{\rm c}-\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ with larger orbital angular momentum has never been performed before. By solving the coupled-channel Schrödinger equations with the one meson exchange potentials that respected to the heavy quark spin and chiral symmetries, we studied the hidden-charm hadronic molecules with $I(J^P)=1/2(3/2^\pm)$ and $1/2(5/2^\pm)$. We conclude that the $J^P$ assignment of the observed pentaquarks is $3/2^+$ for $P^+_{\rm c}(4380)$ and $5/2^-$ for $P^+_{\rm c}(4450)$, which is agreement with the results of the LHCb analysis. In addition, we give predictions for other $J^P=3/2^\pm$ states at 4136.0, 4307.9 and 4348.7 MeV in $J^P=3/2^-$, and 4206.7 MeV in $J^P=3/2^+$, which can be further investigated by means of experiment.

hep-ph↗
arXiv2016

Strangeness suppression in the unquenched quark model

In this contribution, we discuss the strangeness suppression in the proton in the framework of the unquenched quark model. The theoretical results are in good agreement with the values extracted from CERN and JLab experiments.

nucl-th↗
arXiv2014

Valence and sea quarks in the nucleon

In this contribution, we discuss the spin and flavor content of the proton in the framework of the unquenched quark model, and address the role of valence and sea quarks in the nucleon.

nucl-th↗
arXiv2011

A quark-diquark baryon model

A simple quark-diquark model for the baryons is constructed as a partial solution to the well known missing resonances problem. A complete classification of the baryonic states in the quark-diquark framework is given and the spectrum is calculated through a mass formula built to reproduce the rotational and vibrational Regge trajectories.

hep-ph↗
arXiv2008

Tetraquark spectroscopy

A complete classification of tetraquark states in terms of the spin-flavor, color and spatial degrees of freedom was constructed. The permutational symmetry properties of both the spin-flavor and orbital parts of the quark-quark and antiquark-antiquark subsystems are discussed. This complete classification is general and model-independent, and is useful both for model-builders and experimentalists. The total wave functions are also explicitly constructed in the hypothesis of ideal mixing; this basis for tetraquark states will enable the eigenvalue problem to be solved for a definite dynamical model. This is also valid for diquark-antidiquark models, for which the basis is a subset of the one we have constructed. An evaluation of the tetraquark spectrum is obtained from the Iachello mass formula for normal mesons, here generalized to tetraquark systems. This mass formula is a generalizazion of the Gell-Mann Okubo mass formula, whose coefficients have been upgraded by means of the latest PDG data. The ground state tetraquark nonet was identified with $f_{0}(600)$, $κ(800)$, $f_{0}(980)$, $a_{0}(980)$. The mass splittings predicted by this mass formula are compared to the KLOE, Fermilab E791 and BES experimental data. The diquark-antidiquark limit was also studied.

hep-ph↗
arXiv2008

Heavy quarkonium hybrids from Coulomb gauge QCD

Using the non-relativisitc reduction of Coulomb gauge QCD we compute spectrum of the low mass hybrid mesons containing a heavy quark-antiquark pair. The gluon degrees of freedom are treated in the mean field approximation calibrated to the gluelump spectrum. We discuss the role of the non-abelian nature of the QCD Coulomb interaction in the ordering of the spin-parity levels.

hep-ph↗
arXiv2007

Gluelump spectrum from Coulomb gauge QCD

We compute the energy spectrum of gluelumps defined as gluonic excitations bound to a localized, static octet source. We are able to reproduce the nontrivial ordering of the spin-parity levels and show how this is related to the non-abelian part of the Coulomb interaction between color charges.

hep-ph↗
arXiv2007

Tetraquark spectroscopy

A complete classification of $qq \bar q \bar q$ tetraquark states in terms of the spin-flavour, colour and spatial degrees of freedom has been constructed. The permutational symmetry properties of both the spin-flavour and orbital parts of the $qq$ and $\bar{q}\bar{q}$ subsystems are discussed. This complete classification is general and model independent and it is useful both for model builders and experimentalists. The total wave functions are also explicitly constructed in the hypothesis of ideal mixing; this basis for tetraquark states will enable the eigenvalue problem to be solved for a definite dynamical model. An evaluation of the tetraquark spectrum is obtained from the Iachello mass formula for normal mesons, here generalized to tetraquark systems. This mass formula is a generalization of the Gell-Mann Okubo mass formula, whose coefficients have been upgraded by a study of the latest PDG data. The ground state tetraquark nonet is identified with $f_{0}(600),κ(800), f_{0}(980), a_{0}(980)$. The mass splittings predicted by the Iachello mass formula are in agreement with the KLOE, Fermilab E791 and BES experimental data.

hep-ph↗
arXiv2006

Spectroscopy of tetraquark mesons

A classification of tetraquark states in terms of the spin-flavour, colour and spatial degrees of freedom has been constructed. The permutational symmetry properties of both the spin-flavour and orbital parts of the quark-quark and antiquark-antiquark subsystems are briefly discussed. This classification is useful both for model-builders and experimentalists. An evaluation of the tetraquark spectrum is obtained from a Iachello mass formula for tetraquark systems. The ground state tetraquark nonet is identified with $f_{0}(600)$, $κ(800)$, $f_{0}(980)$, $a_{0}(980)$. The mass splittings predicted by this mass formula are in agreement with the KLOE, Fermilab E791 and BES experimental data.

hep-ph↗
arXiv2006

Tetraquark states and spectrum

A general classification of tetraquark states in terms of the spin-flavour, colour and spatial degrees of freedom has been constructed. The permutational symmetry properties of both the spin-flavour and orbital parts of the quark-quark and antiquark-antiquark subsystems are discussed in short. This classification is model indipendent and useful both for model-builders and experimentalists. An evaluation of the tetraquark spectrum is obtained from a generalization of a Iachello mass formula, originally developed for the $q\bar q$ mesons. The ground state tetraquark nonet is identified with $f_{0}(600)$, $κ(800)$, $f_{0}(980)$, $a_{0}(980)$.

hep-ph↗