Meson-meson Interaction Research Articles

Role of triangle singularity in the decay process D0→π+π−f0(980) , f0→π+π−

We study the process $D^0 \to \pi^+ \pi^- f_0(980),\ f_0 \to \pi^+ \pi^-$ by introducing the triangle mechanism, in which $f_0(980)$ is considered to be dynamically generated from the meson-meson interaction. For the total contribution of this process, the contribution of the triangular loop formed by $K^{*} \bar{K} K$ particles could generate a triangular singularity of about 1418 MeV. We calculate the differential decay width of this process and show a narrow peak of about 980 MeV in the $\pi^+ \pi^-$ invariant mass distribution, which comes from $f_0$ decay. For the $M_{inv}(\pi f_0)$ invariant mass distribution, we obtain a finite peak at 1418 MeV, which is consistent with the triangle singularity.

χc1(2p): an overshadowed charmoniumlike resonance

A thorough study of the JPC = 1++ elastic {D}^0{overline{D}}^{ast 0} and D+D∗− scattering, where the form of the meson-meson interaction is inferred from lattice QCD calculations of string breaking, is carried out for center-of-mass energies up to 4 GeV. We show that the presence of χc1(3872), which can be naturally assigned to either a bound or virtual charmoniumlike state close below the {D}^0{overline{D}}^{ast 0} threshold, can overshadow a quasiconventional charmoniumlike resonance lying above threshold. This makes difficult the experimental detection of this resonance through the {D}^0{overline{D}}^{ast 0} and D+D∗− channels, despite being its expected main decay modes. We analyze alternative strong and electromagnetic decay modes. Comparison with existing data shows that this resonance may have already been observed through its decay to ωJ/ψ.

Investigation of the meson-meson interaction

In the framework of the quark delocalization color screening model, we investigate the meson-meson interaction in the four-quark system with the three flavors $u, d$, and $s$. The calculation of the effective potentials of all the $S$-wave states shows that for most states the interaction between two vector mesons is attractive, the one between a pseudoscalar meson and a vector meson is repulsive or weakly attractive, and the one between two pseudoscalar mesons is always repulsive. However, there are still some exceptions. The interaction of the $IJ=00\phantom{\rule{4pt}{0ex}}\ensuremath{\pi}\ensuremath{\pi}$ channel is attractive, while the one of the $IJ=02\phantom{\rule{4pt}{0ex}}\ensuremath{\phi}\ensuremath{\phi}$ channel is repulsive. So it is difficult to use the $S$-wave $\ensuremath{\phi}\ensuremath{\phi}$ state to explain the $X(2239)$ at present calculation. The $S$-wave $\ensuremath{\rho}\ensuremath{\rho}$ states are more likely to be resonance states, which are worthy of investigating in future work. The study of the contribution of each interaction term shows that both the one-gluon exchange and the kinetic energy interaction are important in the interaction between two mesons. The study of the variation of the delocalization parameter indicates that the contribution of the kinetic energy relates to the intermediate-range attraction mechanism in the quark delocalization color screening model (QDCSM), which is achieved by the quark delocalization.

Quarkonium interactions with (hot) hadronic matter

In this work, we present an updated study about the interactions of quarkonia with surrounding hadronic medium. The meson-meson interactions are described with a chiral effective Lagrangian within the framework of unitarized coupled channel amplitudes. In particular, we extend a previous work performed in the charmonium sector by calculating the cross-sections for $\Upsilon$ scattering by light pseudoscalar mesons ($\pi, K, \eta$) and vector mesons ($\rho, K^\ast, \omega$). We evaluate the relevant channels and compare the results with existing literature. The analysis is completed by including the finite-temperature effects in the unitarized scattering amplitudes for both quarkonium and bottomonium sectors.

$\tau^{-}\rightarrow \nu_{\tau} M_{1}M_{2}$τ-→ντM1M2, with M1, M2 pseudoscalar or vector mesons

We perform a calculation of the $\tau^- \to \nu_{\tau} M_1 M_2$, with $M_1, M_2$ either pseudoscalar or vector mesons using the basic weak interaction and angular momentum algebra to relate the different processes. The formalism also leads to a different interpretation of the role played by $G$-parity in these decays. We also observe that, while $p$-wave $M_1 M_2$ production is compatible with chiral perturbation theory and experiment, $VP$ and $VV$ $p$-wave production is clearly incompatible with experiment and we develop the formalism also in this case. We compare our results with experiment and make predictions for unmeasured decays, and we show the value of these reactions, particularly if the $M_1 M_2$ mass distribution is measured, as a tool to learn about the meson-meson interaction and the nature of some resonances, coupling to two mesons, which are produced in such decays.

Impact of unitarization on the J/ψ-light meson cross section

Hidden charm mesons continue playing an essential role as relevant probes to understand the evolution of partonic matter. It is expected that the charmonia that survived the quark-gluon plasma phase suffer collisions with other particles composing the hadronic matter. In this work, we intend to contribute on this subject by presenting an updated study about the interactions of J/ψ with surrounding hadronic medium. The meson-meson interactions are described with a SU(4) effective Lagrangian, and within the framework of unitarized coupled channel amplitudes projected onto s-wave. The symmetry is explicitly broken to SU(3) by suppression of the interactions driven by charmed mesons. We calculate the cross sections for J/ψ scattering by light pseudoscalar mesons (π,K,η) and vector mesons (ρ,K⁎,ω), as well as their inverse processes. Keeping the validity of this present approach in the low CM energy range, the most relevant channels are evaluated and a comparison of the findings with existing literature is performed.

Properties of open and hidden charm mesons in light quark matter

In this work we study the implications of light-quark pionic matter at finite temperatures on the properties of open and hidden charm mesons. The meson-meson interactions are described by means of a chiral unitary approach accounting for coupled channels and the finite temperature effects are included using the Imaginary Time Formalism. The key observables presented here are the spectral function and the pion-induced width at finite temperatures for the mesons D, D* and most importantly J/ψ.

Properties of open and hidden charm mesons in light quark matter

In this work we study the implications of light-quark pionic matter at finite temperatures on the properties of open and hidden charm mesons. The meson-meson interactions are described by means of a chiral unitary approach accounting for coupled channels effects. The in-medium Lippmann-Schwinger Equations, which consider the change in self-energy that the mesons acquire from interacting with the surrounding pionic matter, are solved self-consistently, and the spectral functions of the mesons in the hot pion bath are obtained. It is observed that the charmed mesons develop a quite substantial pion-induced width, being of several tens at a temperature of 150 MeV. The $J/\Psi$ meson stays narrow, but its pionic width at 150 MeV, found to be around 0.1 MeV, is already larger that its vacuum width.

Mass spectra of meson molecular states for heavy and light sectors

We obtain mass spectra of the light and heavy meson-antimeson (molecular states) sectors by using a nonrelativistic potential model with Coulomb and one pion exchange potential terms for meson-meson interaction. The digamma decay widths are also obtained for the light sector. We compare our results with available experimental and theoretical data.

$$f_0(500)$$ f 0 ( 500 ) , $$f_0(980)$$ f 0 ( 980 ) , and $$a_0(980)$$ a 0 ( 980 ) production in the $$\chi _{c1} \rightarrow \eta \pi ^+\pi ^-$$ χ c 1 → η π + π - reaction

We study the $\chi_{c1} \to \eta \pi^+ \pi^-$ decay, paying attention to the production of $f_0(500)$, $f_0(980)$ and $a_0(980)$ from the final state interaction of pairs of mesons that can lead to these three mesons in the final state, which is implemented using the chiral unitary approach. Very clean and strong signals are obtained for the $a_0(980)$ excitation in the $\eta \pi$ invariant mass distribution and for the $f_0(500)$ in the $\pi^+ \pi^-$ mass distribution. A smaller, but also clear signal for the $f_0(980)$ excitation is obtained. The results are contrasted with experimental data and the agreement found is good, providing yet one more test in support of the picture where these resonances are dynamically generated from the meson-meson interaction.

$${\bar{B}}^0$$ B ¯ 0 , $$B^{-}$$ B - and $${\bar{B}}^0_s$$ B ¯ s 0 decays into $$J/\psi $$ J / ψ and $$K {\bar{K}}$$ K K ¯ or $$\pi \eta $$ π η

We study the $\bar B^0_s \to J/\psi K^+ K^-$, $\bar B^0 \to J/\psi K^+ K^-$, $B^- \to J/\psi K^0 K^-$, $\bar B^0 \to J/\psi \pi^0 \eta$ and $B^- \to J/\psi \pi^- \eta$ decays and compare their mass distributions with those obtained for the $\bar B^0_s \to J/\psi \pi^+ \pi^-$ and $\bar B^0 \to J/\psi \pi^+ \pi^-$. The approach followed consist in a factorization of the weak part and the hadronization part into a factor which is common to all the processes. Then what makes the reactions different are some trivial Cabibbo-Kobayashi-Maskawa matrix elements and the weight by which the different pairs of mesons appear in a primary step plus their final state interaction. These elements are part of the theory and thus, up to a global normalization factor, all the invariant mass distributions are predicted with no free parameters. Comparison is made with the limited experimental information available. Further comparison of these results with coming LHCb measurements will be very valuable to make progress in our understanding of the meson-meson interaction and the nature of the low lying scalar meson resonances, $f_0(500), f_0(980)$ and $a_0(980)$.

MANY-BODY FORCES IN THE EQUATION OF STATE OF HYPERONIC MATTER

In this work we introduce an extended version of the formalism proposed originally by Taurines et al. that considers the effects of many-body forces simulated by non-linear self-couplings and meson-meson interaction contributions. In this extended version of the model, we assume that matter is at zero temperature, charge neutral and in beta-equilibrium, considering that the baryon octet interacts by the exchange of scalar-isoscalar ($\sigma$,$\,\sigma^*$), vector-isoscalar ($\omega$,$\,\phi$), vector-isovector ($\varrho$) and scalar-isovector ($\delta$) meson fields. Using nuclear matter properties, we constrain the parameters of the model that describe the intensity of the indirectly density dependent baryon-meson couplings to a small range of possible values. We then investigate asymmetric hyperonic matter properties. We report that the formalism developed in this work is in agreement with experimental data and also allows for the existence of massive hyperon stars (with more than $2M_{\odot}$) with small radii, compatible with astrophysical observations.

F1(1285) decays into a0(980)π0, f0(980)π0 and isospin breaking

We evaluate the decay width for the processes $f_1(1285) \to \pi^0 a_0(980)$ and $f_1(1285) \to \pi^0 f_0(980)$ 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 $\pi \eta, K \bar K$ and $\pi \pi, K \bar K$ respectively. We use a triangular mechanism similar to that of the $\eta(1405) \to \pi \pi \eta$, which provides a decay width for $f_1(1285) \to \pi^0 a_0(980)$ 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 $f_1(1285) \to \pi^0 f_0(980)$, which appears when we consider different masses for the charged and neutral kaons, and show that it is much more suppressed than in the $\eta(1405) \to \pi \pi \eta$ case, but gives rise to a narrow shape of the $\pi^+ \pi^-$ distribution similar to the one found in the $\eta(1405) \to \pi \pi \eta$ decay.

Improvement ofππamplitudes and correct position of theσpole

Meson-meson interaction amplitudes especially ππ scattering amplitudes are often used incorrectly. It also applies to parameters of the σ meson. These causes two sig- nificant problems: threshold behavior and position of the σ pole which is suspicious. We modified multichannel S- and P- wave amplitudes for the ππ scattering, using dispersion relations with imposed crossing symmetry condition. The amplitudes are modified in the low-energy region to improve their consistency with experimental data and the dispersion relations. Agreement with data is achieved for both amplitudes from the threshold up to 1800 MeV and with dispersion relations up to 1100 MeV. Consequences of the applied modifications, e.g. changes of the S-wave lowest-pole positions, are presented.

Isospin breaking andf0(980)-a0(980) mixing in theη(1405) →π0f0(980) reaction

We make a theoretical study of the η (1405) → π 0 f 0 (980) and η (1405) → π 0 a 0 (980) reactions to determine the isospin violation and the mixing of the f 0 (980) and a 0 (980) resonances. We make use of the chiral unitary approach where these two resonances appear as dynamically generated by the meson-meson interaction provided by chiral Lagrangians. We obtain a very narrow shape for the f 0 (980) production in agreement with a BES experiment. As to the amount of isospin violation, assuming constant vertices for the primary η (1405) → π 0 K K and η (1405) → π 0 π 0 η production, we find results which are much smaller than found in the experimental BES paper. The problem is solved by using the primary production driven by η' → K *K followed by K ∗ → K π . Thus, we can predict absolute values for the ratio Γ(π 0 ,π + π − )/Γ(π 0 ,π 0 η ) which are in fair agreement with experiment.

Hidden beauty molecules within the local hidden gauge approach and heavy quark spin symmetry

Using a coupled channel unitary approach, combining the heavy quark spin symmetry and the dynamics of the local hidden gauge, we investigate the meson-meson interaction with hidden beauty and obtain several new states. Both $I=0$ and $I=1$ states are analyzed, and it is shown that in the $I=1$ sector, the interactions are too weak to create any bound states within our framework. In total, we predict with confidence the existence of six bound states and six more possible weakly bound states. The existence of these weakly bound states depends on the influence of the coupled channel effects.

Isospin breaking andf0(980)-a0(980)mixing in theη(1405)→π0f0(980)reaction

We make a theoretical study of the $\eta(1405) \to \pi^{0} f_0(980)$ and $\eta(1405) \to \pi^{0} a_0(980)$ reactions with an aim to determine the isospin violation and the mixing of the $f_0(980)$ and $a_0(980)$ resonances. We make use of the chiral unitary approach where these two resonances appear as composite states of two mesons, dynamically generated by the meson-meson interaction provided by chiral Lagrangians. We obtain a very narrow shape for the $f_0(980)$ production in agreement with a BES experiment. As to the amount of isospin violation, or $f_0(980)$ and $a_0(980)$ mixing, assuming constant vertices for the primary $\eta(1405)\rightarrow \pi^{0}K\bar{K}$ and $\eta(1405)\rightarrow \pi^{0}\pi^{0}\eta$ production, we find results which are much smaller than found in the recent experimental BES paper, but consistent with results found in two other related BES experiments. We have tried to understand this anomaly by assuming an I=1 mixture in the $\eta(1405)$ wave function, but this leads to a much bigger width of the $f_0(980)$ mass distribution than observed experimentally. The problem is solved by using the primary production driven by $\eta' \to K^* \bar K$ followed by $K^* \to K \pi$, which induces an extra singularity in the loop functions needed to produce the $f_0(980)$ and $a_0(980)$ resonances. Improving upon earlier work along the same lines, and using the chiral unitary approach, we can now predict absolute values for the ratio $\Gamma(\pi^0, \pi^+ \pi^-)/\Gamma(\pi^0, \pi^0 \eta)$ which are in fair agreement with experiment. We also show that the same results hold if we had the $\eta(1475)$ resonance or a mixture of these two states, as seems to be the case in the BES experiment.

Dynamical implications of gluonic excitations in meson-meson systems

We study meson-meson interactions using an extended $q^2\bar{q}^2(g)$ basis that allows calculating coupling of an ordinary meson-meson system to a hybrid-hybrid one. We use a potential model matrix in this extended basis which at quark level is known to provide a good fit to numerical simulations of a $q^2\bar{q}^2$ system in pure gluonic theory for static quarks in a selection of geometries. We use a combination of resonating group method formalism and Born approximation to include the quark motion using wave functions of a $q\bar{q}$ potential within a cluster. This potential is taken to be quadratic for ground states and has an additional smeared $\frac{1}{r}$ (Gaussian) for the matrix elements between hybrid mesons. For the parameters of this potential, we use values chosen to 1) minimize the error resulting from our use of a quadratic potential and 2) best fit the lattice data for differences of $\Sigma_{g}$ and $\Pi_{u}$ configurations of the gluonic field between a quark and an antiquark. At the quark (static) level, including the gluonic excitations was noted to partially replace the need for introducing many-body terms in a multi-quark potential. We study how successful such a replacement is at the (dynamical) hadronic level of relevance to actual hard experiments. Thus we study effects of both gluonic excitations and many-body terms on mesonic transition amplitudes and the energy shifts resulting from the second order perturbation theory (i.e. from the respective hadron loops). The study suggests introducing both energy and orbital excitations in wave functions of scalar mesons that are modelled as meson-meson molecules or are supposed to have a meson-meson component in their wave functions.

GLUEBALL-DILATON AS AN ALTERNATIVE TO DARK MATTER IN NEUTRON STARS

We study cold nuclear matter based on a mean field description of baryons bound by the exchange of scalar-isoscalar, vector-isoscalar, scalar-isovector and vector-isovector meson fields as well as the glueball field. For this task, we use an extended version of the effective model with derivative couplings with genuine many-body forces simulated by nonlinear self-couplings and meson-meson interaction terms involving scalar-isoscalar (σ, σ*), vector-isoscalar (ω, ɸ), vector-isovector (ϱ), scalar-isovector (δ) meson and the glueball fields. In our approach, the realization of the broken scale invariance of quantum chromodynamics is achieved through the introduction of a dilaton field. The effective model with dilatons is the applied to the description of neutron stars.

Low-lying even-parity meson resonances and spin-flavor symmetry

A study is presented of the $s-$wave meson-meson interactions involving members of the $\rho-$nonet and of the $\pi-$octet. The starting point is an SU(6) spin-flavor extension of the SU(3) flavor Weinberg-Tomozawa Lagrangian. SU(6) symmetry breaking terms are then included to account for the physical meson masses and decay constants, while preserving partial conservation of the axial current in the light pseudoscalar sector. Next, the $T-$matrix amplitudes are obtained by solving the Bethe Salpeter equation in coupled-channel with the kernel built from the above interactions. The poles found on the first and second Riemann sheets of the amplitudes are identified with their possible Particle Data Group (PDG) counterparts. It is shown that most of the low-lying even parity PDG meson resonances, specially in the $J^P=0^+$ and $1^+$ sectors, can be classified according to multiplets of the spin-flavor symmetry group SU(6). The $f_0(1500)$, $f_1(1420)$ and some $0^+(2^{++})$ resonances cannot be accommodated within this SU(6) scheme and thus they would be clear candidates to be glueballs or hybrids. Finally, we predict the existence of five exotic resonances ($I \ge 3/2$ and/or $|Y|=2$) with masses in the range 1.4--1.6 GeV, which would complete the $27_1$, $10_3$, and $10_3^*$ multiplets of SU(3)$\otimes$SU(2).