arXiv subjects

J. M. Dias

Publications and source records attributed to J. M. Dias.

31 records · Page 2Linked to original sources

arXiv2016

$f_0(980)$ production in $D_s^+ \rightarrow π^+ \, π^+ \, π^-$ and $D_s^+ \rightarrow π^+ \, K^+ \, K^-$ decays

We study the $D_s^+ \rightarrow π^+ \, π^+ \, π^-$ and $D_s^+ \rightarrow π^+ \, K^+ \, K^-$ decays adopting a mechanism in which the $D_s^+$ meson decays weakly into a $π^+$ and a $q\bar{q}$ component, which hadronizes into two pseudoscalar mesons. The final state interaction between these two pseudoscalar mesons is taken into account by using the Chiral Unitary approach in coupled channels, which gives rise to the $f_0(980)$ resonance. Hence, we obtain the invariant mass distributions of the pairs $π^+ π^-$ and $K^+ K^-$ after the decay of that resonance and compare our theoretical amplitudes with those available from the experimental data. Our results are in a fair agreement with these data, and a $f_0(980)$ signal is seen in both the $π^+π^-$ and $K^+K^-$ distributions.

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arXiv2016

A QCD sum rule calculation of the $X^\pm(5568) \to B_{s}^0π^\pm$ decay width

To understand the nature of the $X(5568)$, recently observed in the mass spectrum of the $B_{s}^0π^\pm$ system by the D0 Collaboration, we have investigated, in a previous work, a scalar tetraquark (diquak-antidiquark) structure for it, within the two-point QCD sum rules method. The result found for its mass agrees well with the experimental value. Encouraged by this finding we now extend our calculations to obtain the decay width of $X(5568)$ to $B_{s}^0π^\pm$ using the three-point QCD sum rule. We obtain a value of $(20.4\pm8.7)\MeV$, which, on comparing with the experimental value of $21.9\pm6.4 (\mbox{sta})^{+5.0}_{-2.5}(\mbox{syst}) \MeV/c^2$, reinforces the scalar four quark nature of $X(5568)$.

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arXiv2015

$f_1(1285)$ decays into $a_0(980)π^0$, $f_0(980)π^0$ and isospin breaking

We evaluate the decay width for the processes $f_1(1285) \to π^0 a_0(980)$ and $f_1(1285) \to π^0 f_0(980)$ taking into account that all three resonances are dynamically generated from the meson-meson interaction, the $f_1(1285)$ from $K^* \bar K -c.c$ and the $a_0(980)$, $f_0(980)$ from $πη, K \bar K$ and $ππ, K \bar K$ respectively. We use a triangular mechanism similar to that of the $η(1405) \to ππη$, which provides a decay width for $f_1(1285) \to π^0 a_0(980)$ with a branching fraction of the order of 30%, in agreement with experiment. At the same time we evaluate the decay width for the isospin forbidden $f_1(1285) \to π^0 f_0(980)$, which appears when we consider different masses for the charged and neutral kaons, and show that it is much more suppressed than in the $η(1405) \to ππη$ case, but gives rise to a narrow shape of the $π^+ π^-$ distribution similar to the one found in the $η(1405) \to ππη$ decay.

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arXiv2014

Study of $B\bar{B}^$ and $B^\bar{B}^*$ interactions in $I=1$ and relationship to the $Z_b(10610)$, $Z_b(10650)$ states

We use the local hidden gauge approach in order to study the $B\bar{B}^*$ and $B^*\bar{B}^*$ interactions for isospin I=1. We show that both interactions via one light meson exchange are not allowed by OZI rule and, for that reason, we calculate the contributions due to the exchange of two pions, interacting and noninteracting among themselves, and also due to the heavy vector mesons. Then, to compare all these contributions, we use the potential related to the heavy vector exchange as an effective potential corrected by a factor which takes into account the contribution of the others light mesons exchange. In order to look for poles, this effective potential is used as the kernel of the Bethe-Salpeter equation. As a result, for the $B\bar{B}^*$ interaction we find a loosely bound state with mass in the range $10587-10601$ MeV, very close to the experimental value of the $Z_b(10610)$ reported by Belle Collaboration. For the $B^*\bar{B}^*$ case, we find a cusp at $10650$ MeV for all spin $J=0,\,1,\,2$ cases.

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arXiv2014

Signature of an $h_1$ state from $J/ψ\to ηK^{0}\bar{K}^{0}$ and theoretical description of the $Z_c(3900)$ and $Z_c(4020)$ as $D \bar D^$ and $D^ \bar D^*$ molecular states

In this talk we address two topics: The first one is an empirical explanation in terms of a new state $h_1$ of the peak in the $K^{*0}\bar{K}^{*0}$ invariant mass distribution close to threshold of this channel in the $J/ψ\to ηK^{*0}\bar{K}^{*0}$ decay. The second one is a theoretical description of the isospin $I=1$ $Z_c(3900)$ and $Z_c(4020)$ states in terms of molecular states of $D \bar D^*+ cc$ and $D^* \bar D^*$.

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arXiv2014

Prediction of an $I=1$ $D \bar D^*$ state and relationship to the claimed $Z_c(3900)$, $Z_c(3885)$

We study here the interaction of $D \bar D^*$ in the isospin $I=1$ channel in the light of recent theoretical advances that allow to combine elements of the local hidden gauge approach with heavy quark spin symmetry. We find that the exchange of light $q \bar q$ is OZI suppressed and, thus, we concentrate on the exchange of heavy vectors and of two pion exchange. The latter is found to be small compared to the exchange of heavy vectors, which then determines the strength of the interaction. A barely $D\bar{D}^*$ bound state decaying into $η_cρ$ and $πJ/ψ$ is found. At the same time we reanalyze the data of the BESIII experiment on $e^+ e^- \to π^{\pm} (D \bar D^*)^\mp$, from where a $Z_c(3885)$ state was claimed, associated to a peak in the $(D \bar D^*)^\mp$ invariant mass distribution close to threshold, and we find the data compatible with a resonance with mass around $3875$ MeV and width around $30$ MeV. We discuss the possibility that this and the $Z_c(3900)$ state found at BESIII, reconfirmed at 3896 MeV at Belle, or 3885 MeV at CLEO, could all be the same state and correspond to the one that we find theoretically.

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arXiv2014

Prediction of a $Z_c(4000)$ $D^* \bar D^*$ state and relationship to the claimed $Z_c(4025)$

After discussing the OZI suppression of one light meson exchange in the interaction of $D^* \bar D^*$ with isospin I=1, we study the contribution of two pion exchange to the interaction and the exchange of a heavy vector $J/ψ$. We find this latter mechanism weak but enough to barely bind the system in J=2 with a mass around 4000 MeV, while the effect of the two pion exchange is a net attraction but weaker than that from $J/ψ$ exchange. We discuss this state and try to relate it to the $Z_c(4025)$ state, above the $D^* \bar D^*$ threshold, claimed in an experiment at BES from and enhancement of the $D^* \bar D^*$ distribution close to threshold. Together with the results from a recent reanalysis of the BES experiment showing that it is compatible with a J=2 state below threshold around 3990 MeV, we conclude that the BES experiment could be showing the existence of the state that we find in our approach.

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arXiv2013

CHARM 2013: X(4260) as a Mixed Charmonium-Tetraquark State

Using the QCD sum rule approach we study the X(4260) state assuming that it can be described by a mixed charmonium-tetraquark current with $J^{PC}=1^{--}$ quantum numbers. For the mixing angle around $θ=(53.0 \pm 0.5)^0$, we obtain a value for the mass which is in good agreement with the experimental mass of the X(4260). For the decay width into the channel $X \to J/ψππ$, we find the value $Γ_{X \to J/ψππ}=(4.1 \pm 0.6)$ MeV, which is much smaller than the total experimental width $Γ= (108\pm 12)$ MeV. However, considering the experimental upper limits for the decay of the X(4260) into open charm, we conclude that we cannot rule out the possibility of describing this state as a mixed charmonium-tetraquark state.

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arXiv2013

$Z_{c}(3900)$ as a tetraquark state: decay width in QCD sum rules

Supposing the $Z_{c}^{+}(3900)$ as a charged partner of the X(3872), we use the QCD sum rules techinques in order to obtain the coupling constants of the $Z_{c}^{+} \, J/ψ\, π^{+}$, $Z_{c}^{+}\, η_{c}\, ρ^{+}$ and $Z_{c}^{+}\,D^{+}\, \bar{D}^{*}$ vertices and the corresponding decay width of these channels. We considered that the $Z_{c}(3900)$ can be described by a tetraquark current with the $J^{PC}=1^{+-}$ quantum numbers. As a result, we obtained a decay width value in good agreement with the experimental values reported by BESIII and Belle collaborations.

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arXiv2013

Y(3940) as a Mixed Charmonium-Molecule State

Using the QCD sum rules approach we study the mass and decay width of the channel $J/ψ+ ω$ for the $Y(3940)$ state. We assume that it can be described by a mixed charmonium-molecule scalar state, $(χ_{c0})-(D^\ast D^\ast)$ current, with $J^{PC} = 0^{++}$ quantum numbers. For the mixing angle $(76.0 \pm 5.0)^0$, we obtain the value $M = (3.95 \pm 0.11)$ GeV for the mass, which is in good agreement with the experimental mass of the $Y(3940)$ state. For the decay width into the channel $Y \rightarrow J/ψ+ ω$, we find the value $Γ_Y = (1.7 \pm 0.6)$ MeV, which is also compatible with the experimental data. We thus conclude that the present description of the $Y(3940)$ as a mixed charmonium-molecule state is a possible scenario to explain the structure of this state.

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arXiv2013

$Z_c^+(3900)$ decay width in QCD sum rules

We identify the recently observed charmonium-like structure $Z_c^\pm(3900)$ as the charged partner of the X(3872) state. Using standard techniques of QCD sum rules, we evaluate the three-point function and extract the coupling constants of the $Z_c \, J/ψ\, π^+$ and $Z_c \, η_c \, ρ^+$ vertices and the corresponding decay widths in these channels. The good agreement with the experimental data gives support to the tetraquark picture of this state.

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arXiv2012

Y(4260) as a mixed charmonium-tetraquark state

Using the QCD sum rule approach we study the Y(4260) state assuming that it can be described by a mixed charmonium-tetraquark current with $J^{PC}=1^{--}$ quantum numbers. For the mixing angle around $θ\approx (53.0\pm 0.5)^{0}$, we obtain a value for the mass which is in good agreement with the experimental mass of the Y(4260). However, for the decay width we find the value $\Ga_Y \approx (1.0\pm 0.2)$ MeV which is not compatible with the experimental value $\Ga \approx (88\pm 23)$ MeV. Therefore, we conclude that, although we can explain the mass of the Y(4260), this state cannot be described as a mixed charmonium-tetraquark state since, with this assumption, we can not explain its decay width.

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arXiv2011

Relation between $T_{cc,bb}$ and $X_{c,b}$ from QCD

We have studied, using double ratio of QCD (spectral) sum rules, the ratio between the masses of $T_{cc}$ and X(3872) assuming that they are respectively described by the $D-{D}^*$ and $D-\bar{D}^*$ molecular currents. We found (within our approximation) that the masses of these two states are almost degenerate. Since the pion exchange interaction between these mesons is exactly the same, we conclude that if the observed X(3872) meson is a $D\bar{D}^*+c.c.$ molecule, then the $DD^*$ molecule should also exist with approximately the same mass. An extension of the analysis to the $b$-quark case leads to the same conclusion. We also study the SU(3) breakings for the $T^s_{QQ}/T_{QQ}$ mass ratios. Motivated by the recent Belle observation of two $Z_b$ states, we revise our determination of $X_b$ by combining results from exponential and FESR sum rules.

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