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M. E. Bracco

Publications and source records attributed to M. E. Bracco.

At least 19 recordsLinked to original sources
arXiv2021

The $D_sDK^*$ vertex in QCD Sum Rules: form factors and coupling constant

In this work we study the meson vertex $D_sDK^*$ using the QCD sum rules. We compute the three point correlation functions for the three cases of different off-shell mesons. The form factors for each case are fitted to the numerical calculation of the correlation functions and the coupling constant of the vertex is obtained by comparing the form factors at their respective off-shell meson pole. The result obtained for the coupling constant is $g_{D_sDK^*} = 2.29^{+0.65}_{-0.41}$.

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arXiv2017

A QCD sum rules calculation of the $η_c D^* D$ and $η_c D_s^* D_s$ form factors and strong coupling constants

We use the QCD sum rules for the three point correlation functions to compute the strong coupling constants of the meson vertices $η_c D^* D$ and $η_c D_s^* D_s$. We consider perturbative and non-perturbative contributions, working up to dimension five on the OPE. The vertices were studied considering that each one of its three mesons are off-shell alternately. The vertex coupling constant is evaluated through the extrapolation of the three different form factors. The results obtained for the coupling constants are $g_{η_c D^* D} = 5.23^{+1.80}_{-1.38}$ and $g_{η_c D_s^* D_s}=5.55^{+1.29}_{-1.55}$.

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arXiv2015

A QCD sum rules calculation of the $J/ψD_s^* D_s$ strong coupling constant

In this work, we calculate the form factors and the coupling constant of the strange-charmed vertex $J/ψD_s^* D_s$ in the framework of the QCD sum rules by studying their three-point correlation functions. All the possible off-shell cases are considered, $D_s$, $D_s^*$ and $J/ψ$, resulting in three different form factors. These form factors are extrapolated to the pole of their respective off-shell mesons, giving the same coupling constant for the process. Our final result for the $J/ψD_s^* D_s$ coupling constant is $g_{J/ψD^*_s D_s} = 4.30^{+0.42}_{-0.37}\text{GeV}^{-1}$.

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arXiv2015

$B_s B^* K $ and $B_s B K^*$ vertices using QCD sum rules

The form factors and the coupling constant of the $B_s B^* K $ and $B_s B K^*$ vertices are calculated using the QCD sum rules method. Three point correlation functions are computed considering both the heavy and light mesons off-shell in each vertex, from which, after an extrapolation of the QCDSR results at the pole of the off-shell mesons, we obtain the coupling constant of the vertex. The form factors obtained have different behaviors but their simultaneous extrapolation reach the same value of the coupling constant $g_{B_s B^* K}=8.41 \pm 1.23 $ and $g_{B_s BK^*}=3.3 \pm 0.5$. We compare our result with other theoretical estimates and compute the uncertainties of the method.

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arXiv2012

Obtaining the strong coupling constants g_{J/ψD_s D_s} and g_{ϕD_s D_s} from QCD Sum Rules

The form factors and coupling constants of the meson vertices J/ψD_s D_s and ϕD_s D_s were calculated using three point correlation functions within the QCD Sum Rules formalism. We have considered the cases where ϕ, D_s and J/ψmesons are off-shell obtaining, for each vertex, two different form factors and its corresponding coupling constants, namely g_{J/ψD_s D_s} = 6.20^{+0.97}_{-1.15} and g_{ϕD_s D_s} = 1.85^{+0.22}_{-0.23}.

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arXiv2011

$B_s^* B K$ vertex from QCD sum rules

The form factors and the coupling constant of the $B_s^* B K$ vertex are calculated using the QCD sum rules method. Three point correlation functions are computed considering both $K$ and $B$ mesons off-shell and, after an extrapolation of the QCDSR results, we obtain the coupling constant of the vertex. We study the uncertainties in our result by calculating a third form factor obtained when the $B^*_s$ is the off-shell meson, considering other acceptable structures and computing the variations of the sum rules' parameters. The form factors obtained have different behaviors but their simultaneous extrapolations reach to the same value of the coupling constant $g_{B_s^* B K}=10.6 \pm 1.7$. We compare our result with other theoretical estimates.

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arXiv2011

An inspection on the Borel masses relation used in QCD sum rules

In this work, we studied the Borel masses relation used in QCDSR calculations. These masses are the parameters of the Borel transform used when the three point function is calculated. We analised an usual and a more general linear relations. We concluded that a general linear relation between these masses provides the best results regarding the standard deviation.

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arXiv2011

Charm couplings and form factors in QCD sum rules

We review the calculations of form factors and coupling constants in vertices with charm mesons in the framework of QCD sum rules. We first discuss the motivation for this work, describing possible applications of these form factors to heavy ion collisions and to B decays. We then present an introduction to the method of QCD sum rules and describe how to work with the three-point function. We give special attention to the procedure employed to extrapolate results obtained in the deep euclidean region to the poles of the particles, located in the time-like region. We present a table of ready-to-use parametrizations of all the form factors, which are relevant for the processes mentioned in the introduction. We discuss the uncertainties in our results. We also give the coupling constants and compare them with estimates obtained with other methods. Finally we apply our results to the calculation of the cross section of the reaction $J/ψ+ π\rightarrow D + \bar{D^*}$.

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arXiv2010

The B_{s0} meson and the B_{s0}B K coupling from QCD sum rules

We evaluate the mass of the $B_{s0}$ scalar meson and the coupling constant in the $B_{s0} B K$ vertex in the framework of QCD sum rules. We consider the $B_{s0}$ as a tetraquark state to evaluate its mass. We get $m_{B_s0}=(6.04\pm 0.08) \GeV$, which is bigger than predictions supposing it as a $b\bar{s}$ state or a $B\bar{K}$ bound state with $J^{P}=0^+$. To evaluate the $g_{B_{s0}B K}$ coupling we use the three point correlation functions of the vertex, considering $ B_{s0} $ as a normal $b\bar{s}$ state. The obtained coupling constant is: $g_{B_{s0} B K} =(16.3 \pm 3.2) \GeV$. This number is in agreement with light-cone QCD sum rules calculation. We have also compared the decay width of the $\BS\to BK$ process considering the $\BS$ to be a $b\bar{s}$ state and a $BK$ molecular state. The width obtained for the $BK$ molecular state is twice as big as the width obtained for the $b\bar{s}$ state. Therefore, we conclude that with the knowledge of the mass and the decay width of the $\BS$ meson, one can discriminate between the different theoretical proposals for its structure.

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arXiv2010

$D^{*}D ρ$ vertex from QCD sum rules

We calculate the form factors and the coupling constant in the $D^{*}D ρ$ vertex in the framework of QCD sum rules. We evaluate the three point correlation functions of the vertex considering both $ D $ and $ ρ$ mesons off--shell. The form factors obtained are very different but give the same coupling constant: $g_{D^{*}D ρ} = 4.1 \pm 0.1$ GeV$^{-1}$.

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arXiv2009

Hadron production in non linear relativistic mean field models

By using a parametrization of the non-linear Walecka model which takes into account the binding energy of different hyperons, we present a study of particle production yields measured in central Au-Au collision at RHIC. Two sets of different hyperon-meson coupling constants are employed in obtaining the hadron production and chemical freeze-out parameters. These quantities show a weak dependence on the used hyperon-meson couplings. Results are in good overall accordance with experimental data. We have found that the repulsion among the baryons is quite small and, through a preliminary analysis of the effective mesonic masses, we suggest a way to improve the fittings.

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arXiv2008

The meson $Z^+(4430)$ as a tetraquark state

We test the validity of the QCD sum rules applied to the meson $Z^+(4430)$, by considering a diquark-antidiquark type of current with $J^{P}=0^{-}$ and with $J^{P}=1^{-}$. We find that, with the studied currents, it is possible to find an acceptable Borel window. In such a Borel window we have simultaneously a good OPE convergence and a pole contribution which is bigger than the continuum contribution. We get $m_Z=(4.52\pm0.09)\GeV$ and $m_Z=(4.84\pm0.14)\GeV$ for the currents with $J^{P}=0^{-}$ and $J^{P}=1^{-}$ respectively. We conclude that the QCD sum rules results favors $J^{P}=0^{-}$ quantum numbers for the $Z^+(4430)$ meson.

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arXiv2007

ρD^*D^* vertex from QCD sum rules

We calculate the form factors and the coupling constant in the $ρD^* D^*$ vertex in the framework of QCD sum rules. We evaluate the three point correlation functions of the vertex considering both $ρ$ and $D^*$ mesons off--shell. The form factors obtained are very different but give the same coupling constant: $g_{ρD^* D^*} = 6.6 \pm 0.31$. This number is 50% larger than what we would expect from SU(4) estimates.

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arXiv2007

Constraining relativistic models through heavy ion collisions

Relativistic models can be successfully applied to the description of compact star properties in nuclear astrophysics as well as to nuclear matter and finite nuclei properties, these studies taking place at low and moderate temperatures. Nevertheless, all results are model dependent and so far it is unclear whether some of them should be discarded. Moreover, in the regime of hot hadronic matter very few calculations exist using these relativistic models, in particular when applied to particle yields in heavy ion collisions. In the present work we comment on the known constraints that can help the selection of adequate models in this regime and investigate the main differences that arise when the particle production during a Au+Au collision at RHIC is calculated with different models.

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arXiv2007

Coupling constants of $D^*D_sK$ and $D_s^*DK$ processes

We calculate the coupling constants of $D^*D_sK$ and $D_s^*DK$ vertices using the QCD sum rules technique. We compare results obtained in the limit of SU(4) symmetry and found that the symmetry is broken on the order of 40%.

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arXiv2006

Investigating the tetraquark structure of the new mesons

Using the QCD sum rule approach we investigate the possible four-quark structure of the recently observed mesons $D_{sJ}^{+}(2317)$, firstly observed by BaBaR, X(3872), firstly observed by BELLE and $D_0^{*0}(2308)$ observed by BELLE. We use diquark-antidiquark currents and work in full QCD, without relying on $1/m_c$ expansion. Our results indicate that a four-quark structure is acceptable for these mesons.

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