arXiv subjects

M. Bayar

Publications and source records attributed to M. Bayar.

At least 37 records · Page 2Linked to original sources

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.

hep-ph↗

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.

hep-ph↗

arXiv2014

$\bar{K}NN$ Absorption within the Framework of the Fixed Center Approximation to Faddeev equations

We present a method to evaluate the $\bar{K}$ absorption width in the bound $\bar{K}NN$ system. Most calculations of this system ignore this channel and only consider the $\bar{K}N \rightarrow πΣ$ conversion. Other works make a qualitative calculation using perturbative methods. Since the $ Λ(1405) $ resonance is playing a role in the process, the same resonance is changed by the presence of the absorption channels and we find that a full nonperturbative calculation is called for, which we present here. We employ the Fixed Center Approximation to Faddeev equations to account for $\bar{K}$ rescattering on the $ (NN) $ cluster and we find that the width of the states found previously for $ S=0 $ and $ S=1 $ increases by about 30 MeV due to the $\bar{K}NN$ absorption, to a total width of about 80 MeV.

hep-ph↗

arXiv2013

Description of $ρ(1700)$ as a $ρK \bar{K}$ system with the fixed center approximation

We study the $ρK\bar{K}$ system with an aim to describe the $ρ(1700)$ resonance. The chiral unitary approach has achieved success in a description of systems of the light hadron sector. With this method, the $K \bar{K}$ system in the isospin sector $I=0$, is found to be a dominant component of the $f_0 (980)$ resonance. Therefore, by regarding the $K\bar{K}$ system as a cluster, the $f_0 (980)$ resonance, we evaluate the $ρK\bar{K}$ system applying the fixed center approximation to the Faddeev equations. We construct the $ρK$ unitarized amplitude using the chiral unitary approach. As a result, we find a peak in the three-body amplitude around 1739 MeV and a width of about 227 MeV. The effect of the width of $ρ$ and $f_0 (980)$ is also discussed. We associate this peak to the $ρ(1700)$ which has a mass of $1720 \pm 20$ MeV and a width of $250 \pm 100$ MeV.

hep-ph↗

arXiv2013

Study of the $\bar K N$ system and coupled channels in a finite volume

We investigate the $\bar KN$ and coupled channels system in a finite volume and study the properties of the $Λ(1405)$ resonance. We calculate the energy levels in a finite volume and solve the inverse problem of determining the resonance position in the infinite volume. We devise the best strategy of analysis to obtain the two poles of the $Λ(1405)$ in the infinite volume case, with sufficient precision to distinguish them.

nucl-th↗

arXiv2012

Strategy to find the two $Λ(1405)$ states from lattice QCD simulations

Theoretical studies within the chiral unitary approach, and recent experiments, have provided evidence of the existence of two isoscalar states in the region of the $Λ(1405)$. In this paper we use the same chiral approach to generate energy levels in a finite box. In a second step, assuming that these energies correspond to lattice QCD results, we devise the best strategy of analysis to obtain the two states in the infinite volume case, with sufficient precision to distinguish them. We find out that using energy levels obtained with asymmetric boxes and/or with a moving frame, with reasonable errors in the energies, one has a successful scheme to get the two $Λ(1405)$ poles.

hep-lat↗

arXiv2012

The small $K π$ component in the $K^*$ wave functions

We use a recently developed formalism which generalizes the Weinberg's compositeness condition to partial waves higher than s-wave in order to determine the probability of having a $K π$ component in the $K^*$ wave function. A fit is made to the $K π$ phase shifts in p-wave, from where the coupling of $K^*$ to $K π$ and the $K π$ loop function are determined. These ingredients allow us to determine that the $K^*$ is a genuine state, different to a $K π$ component, in a proportion of about 80%.

hep-ph↗

arXiv2012

Narrow bound states of the DNN system

We report on a recent calculation of the properties of the $DNN$ system, a charmed meson with two nucleons. The system is analogous to the $\bar K NN$ system substituting a strange quark by a charm quark. Two different methods are used to evaluate the binding and width, the Fixed Center approximation to the Faddeev equations and a variational calculation. In both methods we find that the system is bound by about 200 MeV and the width is smaller than 40 MeV, a situation opposite to the one of the $\bar K NN$ system and which makes this state well suited for experimental observation.

nucl-th↗

arXiv2012

A prediction of $D^*$-multi-$ρ$ states

We present a study of the many-body interaction between a $D^*$ and multi-$ρ$. We use an extrapolation to SU(4) of the hidden gauge formalism, which produced dynamically the resonances $f_2(1270)$ in the $ρρ$ interaction and $D^*_2(2460)$ in the $ρD^*$ interaction. Then let a third particle, $ρ$, $D^*$, or a resonance collide with them, evaluating the scattering amplitudes in terms of the Fixed Center Approximation of the Faddeev equations. We find several clear resonant structures above $2800\mev$ in the multibody scattering amplitudes. They would correspond to new charmed resonances, $D^*_3$, $D^*_4$, $D^*_5$ and $D^*_6$, which are not yet listed in the PDG, which would be analogous to the $ρ_3(1690)$, $f_4(2050)$, $ρ_5(2350)$, $f_6(2510)$ and $K^*_3(1780)$, $K^*_4(2045)$, $K^*_5(2380)$ described before as multi-$ρ$ and $K^*$-multi-$ρ$ states respectively.

hep-ph↗

arXiv2012

Improved Fixed Center Approximation of the Faddeev equations for the $\bar{K}NN$ system with S=0

We extend the Fixed Center Approximation (FCA) to the Faddeev Equations for the $\bar{K} NN$ system with S=0, including the charge exchange mechanisms in the $\bar{K}$ rescattering which have been ignored in former works within the FCA. We obtain similar results to those found before, but the binding is reduced by 6 MeV. At the same time we also evaluate the explicit contribution the $πN Σ$ intermediate state in the three body system and find that it produces and additional small decrease in the binding of about 3 MeV. The system appears bound by about 35 MeV and the width omitting two body absorption, is about 50 MeV.

nucl-th↗

arXiv2012

A narrow $DNN$ quasi-bound state

The energies and widths of $DNN$ quasi-bound states with isospin I=1/2 are evaluated in two methods, the fixed center approximation to the Faddeev equation and the variational method approach to the effective one-channel Hamiltonian. The $DN$ interactions are constructed so that they dynamically generate the $Λ_c(2595)$ (I=0, $J^π =1/2^-$) resonance state. We find that the system is bound by about 250 MeV from the $DNN$ threshold, $\sqrt{s} \sim 3500$ MeV. Its width including both the mesonic decay and the $D$ absorption, is estimated to be about 20-40 MeV. The I=0 $DN$ pair in the $DNN$ system is found to form a cluster that is similar to the $Λ_c(2595)$.

hep-ph↗

arXiv2012

A new perspective on the Faddeev equations and the $\bar{K}NN$ system from chiral dynamics and unitarity in coupled channels

We review recent work concerning the $\bar{K}N$ interaction and Faddeev equations with chiral dynamics which allow us to look at the $\bar{K}NN$ from a different perspective and pay attention to problems that have been posed in previous studies on the subject. We show results which provide extra experimental evidence on the existence of two $Λ(1405)$ states. We then show the findings of a recent approach to Faddeev equations using chiral unitary dynamics, where an explicit cancellation of the two body off shell amplitude with three body forces stemming from the same chiral Lagrangians takes place. This removal of the unphysical off shell part of the amplitudes is most welcome and renders the approach unambiguous, showing that only on shell two body amplitudes need to be used. With this information in mind we use an approximation to the Faddeev equations within the fixed center approximation to study the $\bar{K}NN$ system, providing answers within this approximation to questions that have been brought before and evaluating binding energies and widths of this three body system. As a novelty with respect to recent work on the topic we find a bound state of the system with spin S=1, like a bound state of $\bar{K}$-deuteron, less bound that the one of S=0, where all recent efforts have been devoted. The width is relatively large in this case, suggesting problems in a possible experimental observation.

hep-ph↗

arXiv2011

Semileptonic transition of $Σ_{b}$ to $Σ$ in Light Cone QCD Sum Rules

We use distribution amplitudes of the light $Σ$ baryon and the most general form of the interpolating current for heavy $Σ_b$ baryon to investigate the semileptonic $Σ_b\rightarrow Σl^+l^-$ transition in light cone QCD sum rules. We calculate all twelve form factors responsible for this transition and use them to evaluate the branching ratio of the considered channel. The order of branching fraction shows that this channel can be detected at LHC.

hep-ph↗

arXiv2011

$NDK$, $\bar{K} DN$ and $ND\bar{D}$ molecules

We investigate theoretically baryon systems made of three hadrons which contain one nucleon and one D meson, and in addition another meson, $\bar{D}, K$ or $\bar{K}$. The systems are studied using the Fixed Center Approximation to the Faddeev equations. The study is made assuming scattering of a $K$ or a $\bar{K}$ on a $DN$ cluster, which is known to generate the $Λ_c(2595)$, or the scattering of a nucleon on the $D\bar{D}$ cluster, which has been shown to generate a hidden charm resonance named X(3700). We also investigate the configuration of scattering of $N$ on the $KD$ cluster, which is known to generate the $D_{s0}^*(2317)$. In all cases we find bound states, with the $NDK$ system, of exotic nature, more bound than the $\bar{K} DN$.

hep-ph↗

arXiv2011

The $\bar{K}NN$ system with chiral dynamics

We have performed a calculation of the scattering amplitude for the three body system $\bar{K}NN$ assuming $\bar{K}$ scattering against a $NN$ cluster, using the Fixed Center approximation to the Faddeev equations. The $\bar{K}N$ amplitudes, which we take from chiral unitary dynamics, govern the reaction and we find a $\bar{K}NN$ amplitude that peaks around 40 MeV below the $\bar{K}NN$ threshold, with a width in $|T|^2$ of the order of 50 MeV for spin 0 and has another peak around 27 MeV with similar width for spin 1. The results are in line with those obtained using different methods but implementing chiral dynamics. The simplicity of the approach allows one to see the important ingredients responsible for the results. In particular we show the effects from the reduction of the size of the $NN$ cluster due to the interaction with the $\bar{K}$ and those from the explicit considiration of the $ πΣN $ channel in the three body equations.

hep-ph↗

arXiv2011

A comparative study on $B \rar K^\ast \ell^+ \ell^-$ and $B \rar K_0^\ast (1430) \ell^+ \ell^-$ decays in the Supersymmetric Models

In this paper, we compare the branching ratio and rate difference of electron channel to muon channel of $B \rar K_0^\ast (1430) \ell^+ \ell^-$ and $B \rar K^\ast \ell^+ \ell^-$decays, where $K_0^\ast (1430)$ is the p--wave scalar meson, in the supersymmetric models. MSSM with $R$ parity is considered since considerable deviation from the standard model predictions can be obtained in $B\rightarrow X_s \ell^-\ell^+$. Taking $C_{Q1}$ and $C_{Q2}$ about one which is consistent with the $B\to K^\astμ^+μ^-$ rate at low dileptonic invariant mass region($1\leq q^2\leq 6$GeV$^2$). It is found that, firstly, the $B \rar K_0^\ast (1430) \ell^+ \ell^-$ $(\ell = μ,\, τ)$ decay is measurable at LHC, secondly, in comparison with $B \rar K^\ast \ell^+ \ell^-$ decay a greater deviation in the $B \rar K_0^\ast (1430) \ell^+ \ell^-$ decay can be seen. Measurement of these observables for the semileptonic rare $B \rar K_0^\ast (1430) \ell^+ \ell^-$, in particular, at low $q^2$ region can give valuable information about the nature of interactions within Standard Model or beyond.

hep-ph↗

arXiv2010

Scalar Quarkonia at Finite Temperature

Masses and decay constants of the scalar quarkonia, $χ_{Q0} (Q=b,c)$ with quantum numbers $I^G(J^{PC})=0^{+}(0^{++})$ are calculated in the framework of the QCD sum rules approach both in vacuum and finite temperature. The masses and decay constants remain unchanged up to $T\simeq100~MeV$ but they start to diminish with increasing the temperature after this point. At near the critic or deconfinement temperature, the decay constants reach approximately to 25% of their values in vacuum, while the masses are decreased about 6% and 23% for bottom and charm cases, respectively. The results at zero temperature are in a good consistency with the existing experimental values and predictions of the other nonperturbative approaches. Our predictions on the decay constants in vacuum as well as the behavior of the masses and decay constants with respect to the temperature can be checked in the future experiments.

hep-ph↗

arXiv2010

The $g_{Σ_QΣ_Qπ}$ Coupling Constant via Light Cone QCD Sum Rules

Using the most general form of the interpolating currents, the coupling constants $g_{Σ_bΣ_bπ}$ and $g_{Σ_cΣ_cπ}$ are calculated within the light cone QCD sum rules approach. It is found that $g_{{Σ_{c}Σ_{c}π}}=-8.0\pm1.7$ and $g_{{Σ_{b}Σ_{b}π}}=-11.0\pm2.1$.

hep-ph↗