arXiv subjects

Marco Cardoso

Publications and source records attributed to Marco Cardoso.

At least 19 recordsLinked to original sources

arXiv2020

Bottomonium resonances with $I = 0$ from lattice QCD correlation functions with static and light quarks

We discuss, how to study $I = 0$ quarkonium resonances decaying into pairs of heavy-light mesons using static potentials from lattice QCD. These static potentials can be obtained from a set of correlation functions containing both static and light quarks. As a proof of concept we focus on bottomonium with relative orbital angular momentum $L = 0$ of the $\bar{b} b$ pair corresponding to $J^{P C} = 0^{- +}$ and $J^{P C} = 1^{- -}$. We use static potentials from an existing lattice QCD string breaking study and compute phase shifts and $\mbox{T}$ matrix poles for the lightest heavy-light meson-meson decay channel. We discuss our results in the context of corresponding experimental results, in particular for $Υ(10860)$ and $Υ(11020)$.

hep-lat↗

arXiv2018

$\bar{b}\bar{b}ud$ tetraquark resonances in the Born-Oppenheimer approximation using lattice QCD potentials

We study tetraquark resonances using lattice QCD potentials for a pair of static antiquarks $\bar{b}\bar{b}$ in the presence of two light quarks $ud$. The system is treated in the Born-Oppenheimer approximation and we use the emergent wave method. We focus on the isospin $I=0$ channel, but consider different orbital angular momenta $l$ of the heavy antiquarks $\bar{b}\bar{b}$. We extract the phase shifts and search for $\mbox{S}$ and $\mbox{T}$ matrix poles on the second Riemann sheet. For orbital angular momentum $l=1$ we find a tetraquark resonance with quantum numbers $I(J^P)=0(1^-)$, resonance mass $m=10576^{+4}_{-4} \, \textrm{MeV}$ and decay width $Γ= 112^{+90}_{-103} \textrm{MeV}$, which can decay into two $B$ mesons.

hep-lat↗

arXiv2017

Tetraquark resonances computed with static lattice QCD potentials and scattering theory

We study tetraquark resonances with lattice QCD potentials computed for two static quarks and two dynamical quarks, the Born-Oppenheimer approximation and the emergent wave method of scattering theory. As a proof of concept we focus on systems with isospin $I = 0$, but consider different relative angular momenta $l$ of the heavy $b$ quarks. We compute the phase shifts and search for $\mbox{S}$ and $\mbox{T}$ matrix poles in the second Riemann sheet. We predict a new tetraquark resonance for $l = 1$, decaying into two $B$ mesons, with quantum numbers $I(J^P) = 0(1^-)$, mass $m = 10576_{-4}^{+4} \, \textrm{MeV}$ and decay width $Γ= 112_{-103}^{+90} \, \textrm{MeV}$.

hep-lat↗

arXiv2017

$u d \bar{b} \bar{b}$ tetraquark resonances with lattice QCD potentials and the Born-Oppenheimer approximation

We study tetraquark resonances with lattice QCD potentials computed for a static bbar bbar pair in the presence of two lighter quarks u d, the Born-Oppenheimer approximation and the emergent wave method. As a proof of concept we focus on the system with isospin I = 0, but consider different relative angular momenta l of the heavy quarks bbar bbar. For l=0 a bound state has already been predicted with quantum numbers I(JP) = 0(1+). Exploring various angular momenta we now compute the phase shifts and search for S and T matrix poles in the second Riemann sheet. We predict a tetraquark resonance for l =1, decaying into two B mesons, with quantum numbers I(JP) = 0(1-), mass m = 10 \, 576^{+4}_{-4} MeV} and decay width Gamma = 112^{+90}_{-103} MeV.

hep-lat↗

arXiv2017

Flux tubes at Finite Temperature

In this work, we show the flux tubes of the quark-antiquark and quark-quark at finite temperature for SU(3) Lattice QCD. The chromomagnetic and chromoelectric fields are calculated above and below the phase transition.

hep-lat↗

arXiv2016

Flux tubes at Finite Temperature

We show the flux tubes produced by static quark-antiquark, quark-quark and quark-gluon charges at finite temperature. The sources are placed in the lattice with fundamental and adjoint Polyakov loops. We compute the square densities of the chromomagnetic and chromoelectric fields above and below the phase transition. Our results are gauge invariant and produced in pure gauge SU(3). The codes are written in CUDA and the computations are performed with GPUs.

hep-lat↗

arXiv2016

Mapping chiral symmetry breaking in the excited baryon spectrum

We study the conjectured "Insensitivity to Chiral Symmetry Breaking" in the highly excited light baryon spectrum. While the experimental spectrum is being measured at JLab and CBELSA/TAPS, this insensitivity remains to be computed theoretically in detail. As the only existing option to have both confinement, highly excited states and chiral symmetry, we adopt the truncated Coulomb gauge formulation of QCD, considering a linearly confining Coulomb term. Adopting a systematic and numerically intensive variational treatment up to 12 harmonic oscillator shells we are able to access several angular and radial excitations. We compute both the excited spectra of $I=1/2$ and $I=3/2$ baryons, up to large spin $J=13/2$, and study in detail the proposed chiral multiplets. While the static-light and light-light spectra clearly show chiral symmetry restoration high in the spectrum, the realization of chiral symmetry is more complicated in the baryon spectrum than earlier expected.

hep-ph↗

arXiv2014

An unitarized model for tetraquarks with a color flip-flip potential

In this work, a color structure dependent flip-flop potential is developed for the two quarks and two antiquarks system. Then, this potential is applied to a microscopic quark model which, by integrating the internal degrees of freedom, is transformed into a model of mesons with non-local interactions. With this, the T matrix for the system is constructed and meson-meson scattering is studied. Tetraquarks states, interpreted as poles of of the T matrix, both bound states and resonances, are found. Special emphasis is given to the truly exotic $qq\bar{Q}\bar{Q}$ system, but some results for the crypto-exotic $qQ\bar{q}\bar{Q}$ are also presented.

hep-ph↗

arXiv2014

$X(3872)$ electromagnetic decay in a coupled-channel model

A multichannel Schrödinger equation with both quark-antiquark and meson-meson components, using a harmonic-oscillator potential for $q\bar{q}$ confinement and a delta-shell string-breaking potential for decay, is applied to the axial-vecor $X(3872)$ and lowest vector charmonia. The model parameters are fitted to the experimental values of the masses of the $X(3872)$, $J/ψ$ and $ψ(2S)$. The wave functions of these states are computed and then used to calculate the electromagnetic decay widths of the $X(3872)$ into $J/ψγ$ and $ψ(2S)γ$.

hep-ph↗

arXiv2014

Unquenched quark-model calculation of X(3872) electromagnetic decays

A recent quark-model description of X(3872) as an unquenched $2\,{}^{3\!}P_1$ $c\bar{c}$ state is generalised by now including all relevant meson-meson configurations, in order to calculate the widths of the experimentally observed electromagnetic decays $X(3872) \to γJ/ψ$ and $X(3872) \to γψ(2S)$. Interestingly, the inclusion of additional two-meson channels, most importantly $D^\pm D^{\star\mp}$, leads to a sizeable increase of the $c\bar{c}$ probability in the total wave function, although the $D^0\bar{D}^{\star0}$ component remains the dominant one. As for the electromagnetic decays, unquenching strongly reduces the $γψ(2S)$ decay rate yet even more sharply enhances the $γJ/ψ$ rate, resulting in a decay ratio compatible with one experimental observation but in slight disagreement with two others. Nevertheless, the results show a dramatic improvement as compared to a quenched calculation with the same confinement force and parameters. Concretely, we obtain $Γ( X(3872) \to γψ(2S) )=28.9$ keV and $Γ( X(3872) \to γJ/ψ)=24.7$ keV, with branching ratio $\mathcal{R}_{γψ}=1.17$.

hep-ph↗

arXiv2014

SU(3) quark-antiquark QCD flux tube

We compute the quark-antiquark flux tube for pure gauge SU(3) in space-time 3 + 1 dimensions. To increase the signal over noise ratio, we apply the improved multihit and extended smearing techniques. We fit the field densities with an appropriate ansatz and we observe both the screening of the color fields and the quantum widening of the flux tube in the mediator plane and in the charge planes.

hep-lat↗

arXiv2012

Study of compact U(1) flux tubes in 3+1 dimensions in lattice gauge theory using GPU's

We utilize Polyakov loop correlations to study (3+1)D compact U(1) flux tubes and the static electron-positron potential in lattice gauge theory. By using field operators it is possible in U(1) lattice gauge theory to probe directly the electric and magnetic fields. In order to improve the signal-to-noise ratio in the confinement phase, we apply the Lüscher-Weiss multilevel algorithm. Our code is written in CUDA, and we run it in NVIDIA FERMI generation GPU's, in order to achieve the necessary performance for our computations.

hep-lat↗

arXiv2012

Colour flux-tubes in static Pentaquark and Tetraquark systems

The colour fields created by the static tetraquark and pentaquark systems are computed in quenched SU(3) lattice QCD, with gauge invariant lattice operators, in a 24^3 x 48 lattice at beta=6.2. We generate our quenched configurations with GPUs, and detail the respective benchmanrks in different SU(N) groups. While at smaller distances the coulomb potential is expected to dominate, at larger distances it is expected that fundamental flux tubes, similar to the flux-tube between a quark and an antiquark, emerge and confine the quarks. In order to minimize the potential the fundamental flux tubes should connect at 120o angles. We compute the square of the colour fields utilizing plaquettes, and locate the static sources with generalized Wilson loops and with APE smearing. The tetraquark system is well described by a double-Y-shaped flux-tube, with two Steiner points, but when quark-antiquark pairs are close enough the two junctions collapse and we have an X-shaped flux-tube, with one Steiner point. The pentaquark system is well described by a three-Y-shaped flux-tube where the three flux the junctions are Steiner points.

hep-lat↗

arXiv2012

Detailed study of quark-antiquark flux tubes and flux tube recombination

In this work we compute the color fields in the mediator plane between a static quark and a static antiquark using quenched lattice QCD. In special, we see the effect of the quark-antiquark distance on the flux tube. To obtain this results an improved multihit technique is developed and an extend smearing technique is used. Then, we also discuss the flux-tubes in a system composed of two quarks and two antiquarks. The ground and first excited states fields are studied for different dispositions of the system.

hep-lat↗

arXiv2012

Tetraquark and the flux tube recombination

Here we study the static potential for the two quarks and two antiquarks system. First this is done using the tetraquark operator, which has been previously used to calculate the static potential. This is found to give good results in the region where the tetraquark is expected to be the ground state, however failing outside it. To repair this, we resort to a variational method. This let us study the first excited state besides the ground state of the system in two different particle dispositions, one where the quarks are on the same side of a rectangle and the other where they are at opposite sides. Results for the field components and for the lagrangian density are presented.

hep-lat↗

arXiv2011

Colour flux-tubes in static Pentaquark systems

The colour fields created by the static tetraquark and pentaquark systems are computed in quenched SU(3) lattice QCD, with gauge invariant lattice operators, in a 24^3 x 48 lattice at beta=6.2 . We generate our quenched configurations with GPUs, and detail the respective benchmanrks in different SU(N) groups. While at smaller distances the coulomb potential is expected to dominate, at larger distances it is expected that fundamental flux tubes, similar to the flux-tube between a quark and an antiquark, emerge and confine the quarks. In order to minimize the potential the fundamental flux tubes should connect at 120o angles. We compute the square of the colour fields utilizing plaquettes, and locate the static sources with generalized Wilson loops and with APE smearing. The tetraquark system is well described by a double-Y-shaped flux-tube, with two Steiner points, but when quark-antiquark pairs are close enough the two junctions collapse and we have an X-shaped flux-tube, with one Steiner point. The pentaquark system is well described by a three-Y-shaped flux-tube where the three flux the junctions are Steiner points.

hep-lat↗

arXiv2011

Study of Tetraquarks with a simple model

Tetraquarks are studied with an approximation which reduces the in- ternal degrees of freedom of the system, using both finite differences and scattering theory. The existence of bound states and resonances is inspected and the masses and widths of the found resonances are calculated.

hep-ph↗

arXiv2011

The chiral crossover, static-light and light-light meson spectra, and the deconfinement crossover

We study the chiral crossover, the spectra of light-light and of static-light mesons and the deconfinement crossover at finite temperature T. Our framework is the confining and chiral invariant quark model, related to truncated Coulomb gauge QCD. Since we are dealing with light quarks, where the linear potential dominates the quark condensate and the spectrum, we only specialize in the linear confining potential for the quark-antiquark interaction. We utilize T dependent string tensions previously fitted from lattice QCD data, and a fit of previously computed dynamically generated constituent quark masses. We scan the T effects on the constituent quark mass, on the meson spectra and on the polyakov loop.

hep-ph↗