Spectroscopy of the All-Charm Tetraquark

We use a non-relativistic model to study the mass spectroscopy of a tetraquark composed by $c \, \bar{c} \, c \, \bar{c}$ quarks in the diquark-antidiquark picture. By numerically solving the Schr\"{o}dinger equation with a Cornell-inspired potential, we separate the four-body problem into three two-body problems. Spin-dependent terms (spin-spin, spin-orbit and tensor) are used to describe the splitting structure of the $c\bar{c}$ spectrum and are also extended to the interaction between diquarks. Recent experimental data on charmonium states are used to fix the parameters of the model and a satisfactory description of the spectrum is obtained. We find that the spin-dependent interaction is sizable in the diquark-antidiquark system, despite of the heavy diquark mass, and that the diquark has a finite size if treated in analogy to the $c\bar{c}$ systems. We find that the lowest $S$-wave $T_{4c}$ tetraquarks might be below their thresholds of spontaneous dissociation into low-lying charmonium pairs, while orbital and radial excitations would be mostly above the corresponding charmonium pair threshold. These states could be investigated in the forthcoming experiments at LHCb and Belle II.Comment: Presented at the XVII International Conference on Hadron Spectroscopy and Structure - Hadron2017, 25-29 September, 2017, University of Salamanca, Salamanca, Spai

Considerations on the Schmid theorem for triangle singularities

We investigate the Schmid theorem, which states that if one has a tree level mechanism with a particle decaying to two particles and one of them decaying posteriorly to two other particles, the possible triangle singularity developed by the mechanism of elastic rescattering of two of the three decay particles does not change the cross section provided by the tree level. We investigate the process in terms of the width of the unstable particle produced in the first decay and determine the limits of validity and violation of the theorem. One of the conclusions is that the theorem holds in the strict limit of zero width of that resonance, in which case the strength of the triangle diagram becomes negligible compared to the tree level. Another conclusion, on the practical side, is that for realistic values of the width, the triangle singularity can provide a strength comparable or even bigger than the tree level, which indicates that invoking the Schmid theorem to neglect the triangle diagram stemming from elastic rescattering of the tree level should not be done. Even then, we observe that the realistic case keeps some memory of the Schmid theorem, which is visible in a peculiar interference pattern with the tree level.Comment: 13 pages, 13 figure

Desenvolvimento de metodologia analítica para a determinação de halofenóis e haloanisóis em papel kraft por microextração em fase sólida e cromatografia gasosa

TCC (graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Físicas e Matemáticas. Curso de Química.A contaminação de papéis por halofenóis e haloanisóis tem trazido problemas para a indústria de papel, devido ao fato de baixas concentrações destes compostos causarem odor e devido às suas propriedades carcinogênicas. Assim, papéis destinados para embalagens de alimentos devem estar livres deste tipo de produto. A Microextração em Fase Sólida (SPME) é uma técnica simples e eficiente para a pré-concentração de amostras que elimina o uso de solventes orgânicos e apresenta poucas etapas em seu procedimento. O enfoque deste trabalho é o desenvolvimento de uma metodologia analítica para a determinação destes compostos em níveis de μg L-1 utilizando o método de SPME seguido por Cromatografia Gasosa e detecção por ionização em chama. O trabalho também consiste na apresentação e estudo de um problema de contaminação de papel por halofenóis e seus respectivos haloanisóis na indústria de fabricação de papéis. Os resultados obtidos nos procedimentos experimentais se mostraram eficientes para a determinação quantitativa dos compostos alvo em matriz aquosa em limites de quantificação de 1 μg L-1 para o 2,4,6-triclorofenol, 2,4,6-tricloroanisol e 2,4,6-tribromoanisol; 5 μg L-1 para 2,4,6-tribromofenol e pentacloroanisol; e valores de 10 μg L-1 para o pentaclorofenol. Uma análise qualitativa em papel também foi executada mostrando bons resultados

Production and mixing of scalar mesons in ηc\eta_c and χc1\chi_{c1} decays

We briefly discuss how the chiral unitary approach in coupled channels and $SU(3)$ symmetry can be used to describe the production of $f_0(500)$, $f_0(980)$ and $a_0(980)$ in the $\chi_{c1} \to \eta \pi^+ \pi^-$ reaction, recently measured by the BESIII collaboration. In this reaction a very strong peak for the $a_0(980)$ can be seen in the $\eta\pi$ invariant mass, while clear signals for the $f_0(500)$ and $f_0(980)$ appear in the one of $\pi^+\pi^-$. Next, we show the predictions made with the same model for the analogous decay $\eta_c \to \eta \pi^+ \pi^-$, which could also be measured experimentally. We discuss the differences of these two reactions which are interesting to test the picture where these scalar mesons are dynamically generated from the interaction of pairs of pseudoscalars. Furthermore, we comment on a new recent work where the same model was used to study the $a_0(980) - f_0(980)$ mixing in the $\chi_{c1} \to \pi^0 \pi^0 \eta$ and $\chi_{c1} \to \pi^0 \pi^+ \pi^-$ reactions, showing that quantitative agreement with the experimental measurement of this mixing, also performed by BESIII, can be obtained, revealing interesting aspects of the dynamics of this process and the importance of coupled channels.Comment: Talk presented at the XVII International Conference on Hadron Spectroscopy and Structure - Hadron2017, 25-29 September, 2017, University of Salamanca, Salamanca, Spain. arXiv admin note: substantial text overlap with arXiv:1707.0722

Molecular Ωc\Omega_c states generated from coupled meson-baryon channels

We have investigated $\Omega_c$ states that are dynamically generated from the meson-baryon interaction. We use an extension of the local hidden gauge to obtain the interaction from the exchange of vector mesons. We show that the dominant terms come from the exchange of light vectors, where the heavy quarks are spectators. This has as a consequence that heavy quark symmetry is preserved for the dominant terms in the $(1/m_Q)$ counting, and also that the interaction in this case can be obtained from the $\textrm{SU(3)}$ chiral Lagrangians. We show that for a standard value for the cutoff regulating the loop, we obtain two states with $J^{P}={1/2}^{-}$ and two more with $J^{P}={3/2}^{-}$, three of them in remarkable agreement with three experimental states in mass and width. We also make predictions at higher energies for states of vector-baryon nature.Comment: New title, extended discussions, new figure, typos corrected. 23 pages, 4 figure