Neutral Vector Meson Research Articles

Exclusive production of double light neutral mesons at the e+e− colliders

In this work we investigate the exclusive production of a pair of light neutral mesons in e+e− annihilation, where the final state bears an even C-parity. The production processes can be initiated via the photon fragmentation or the nonfragmentation mechanism. While the fragmentation contribution can be rigorously accounted, the nonfragmentation contributions are calculated within the framework of collinear factorization, where only the leading-twist light-cone distribution amplitudes (LCDAs) of mesons are considered. Mediately solely by the nonfragmentation mechanism, the production rates of double light neutral pseudoscalar mesons are too small to be observed at the commissioning e+e− facilities. In contrast, the production rates of a pair of light neutral vector mesons are greatly amplified owing to the significant kinematic enhancement brought by the fragmentation mechanism. It is found that, at s=3.77 GeV, after including the destructive interference between the nonfragmentation and fragmentation contributions, the production rates for e+e−→ρ0ρ0 and ρ0ω can be lowered by about 10% and 30% relative to the fragmentation predictions. Future precise measurement of these exclusive double neutral vector meson production channels at BESIII experiment may provide useful constraints on the LCDAs of light vector mesons. Published by the American Physical Society 2024

Lepton flavor violating decays of vector mesons in the MRSSM* *Supported by the Natural Science Foundation of Hebei Province (A2022104001, A2022201017), the Shanxi Scholarship Council of China (2021-31), the youth top-notch talent support program of the Hebei Province, and the Foundation of Baoding University (2018Z01)

In this study, we analyze the rare decays of the neutral vector mesons and in the scenario of the minimal R-symmetric supersymmetric standard model using the effective Lagrangian method. The predicted branching ratios are dominated by the mass insertion parameters , i.e., the off-diagonal inputs, and the contributions of different parts are comparable. Taking into account the experimental constraints on the mass insertion parameters, the predicted branching ratios for the most promising processes are ten orders of magnitude smaller than the present experimental bounds.

Neutral pseudoscalar and vector meson masses under strong magnetic fields in an extended NJL model: Mixing effects

Mixing effects on the mass spectrum of light neutral pseudoscalar and vector mesons in the presence of an external uniform magnetic field $\vec B$ are studied in the framework of a two-flavor NJL-like model. The model includes isoscalar and isovector couplings both in the scalar-pseudoscalar and vector sectors, and also incorporates flavor mixing through a 't Hooft-like term. Numerical results for the $B$ dependence of meson masses are compared with present lattice QCD results. In particular, it is shown that the mixing between pseudoscalar and vector meson states leads to a significant reduction of the mass of the lightest state. The role of chiral symmetry and the effect of the alignment of quark magnetic moments in the presence of the magnetic field are discussed.

1/Nc approximation and universality of vector mesons

In this work, we argue that the observed differences in the value of the vector coupling constant extracted from the decays $\ensuremath{\rho}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$ (${g}_{\ensuremath{\rho}}=6.0$), $\ensuremath{\rho}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ (${g}_{\ensuremath{\rho}}=5.0$) and $\ensuremath{\omega}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ (${g}_{\ensuremath{\rho}}=5.7$), where $l=e$, $\ensuremath{\mu}$, are an indication of the important role played by the $1/{N}_{c}$ corrections in the description of these processes. We show that an emission of a photon by charged meson loops in the ${\ensuremath{\rho}}^{0},\ensuremath{\omega},\ensuremath{\phi}\ensuremath{\rightarrow}\ensuremath{\gamma}$ transitions is a key process that allows to describe above vector meson decays into two leptons with a single value ${g}_{\ensuremath{\rho}}=6.0$. Our result supports the idea of universality of neutral vector mesons and clarifies the role of accounting of $1/{N}_{c}$ corrections to its fulfilment.

How to Detect the Lightest Glueball

We suggest a procedure for detecting the lightest glueball in a head-on collision of photons whose center-of-mass energy is in the range 1.3–2 GeV. We use recent evidence for scattering of light by light in Large Hadron Collider experiments as a phenomenological basis for our suggestion. With this evidence, the cross section of the lightest glueball creation in γγ collisions is estimated to be ~60 nb. The predominant mode of the lightest glueball decay, predicted from the gauge/gravity duality, proves to be the decay into two neutral vector mesons ρ0ρ0. Because the ρ0 decays into π+π–, a drastic increase of the π+π–π+π– yield is expected as the center-of-mass energy approaches the value of the lightest glueball mass. This fact will be the unique signature of the lightest glueball detection.

Study on pure annihilation type B→Vγ decays

We investigate the pure annihilation type radiative $B$ meson decays $B^0 \to \phi \gamma$ and $B_s \to \rho^0(\omega)\gamma$ in the soft-collinear effective theory. We consider three types of contributions to the decay amplitudes, including the direct annihilation topology, the contribution from the electro-magnetic penguin operator and the contribution of the neutral vector meson mixings. The numerical analysis shows that the decay amplitudes are dominated by the $\omega-\phi$ mixing effect in the $B^0 \to \phi\gamma$ and $B_s \to \omega\gamma$ modes. The corresponding decay branching ratios are enhanced about three orders of magnitudes relative to the pure annihilation type contribution in these two decay channels. The decay rate of $B_s \to \rho^0\gamma$ is much smaller than that of $B_s \to \omega\gamma$ because of the smaller $\rho^0-\phi$ mixing. The predicted branching ratios $B(B^{0}\rightarrow\phi\gamma)=(3.99^{+1.67}_{-1.46} )\times10^{-9},\,B(B_s\rightarrow\omega\gamma)=(2.01^{+0.81}_{-0.71} )\times10^{-7}$ are to be tested by the Belle-II and LHC-b experiments.

КАК ОБНАРУЖИТЬ ЛЕГЧАЙШИЙ ГЛЮБОЛ

We suggest a procedure of the lightest glueball detection in a head-on collision of photons whose center-of-mass energy is in the range $1.3-2$ GeV. Recent evidence for the scattering of light by light in experiments at the Large Hadron Collider is used as a phenomenological basis of our suggestion. With this evidence, the cross section of the lightest glueball creation in the $\gamma\gamma$ collisions is estimated to be $\sim 60\,$nb. The predominant mode of the lightest glueball decay, predicted from the gauge/gravity duality, proves to be the decay into two neutral vector mesons $\rho^0\rho^0$. Because $\rho^0$ decays into $\pi^+\pi^-$, a drastic increase in the $\pi^+\pi^-\pi^+\pi^-$ yield is expected as the center-of-mass energy of the colliding photons approaches the value of the lightest glueball mass. This fact may be regarded as the unique signature of the lightest glueball detection.

A dimension five Lorentz-violating nonminimal coupling for mesons in the KLZ model

We investigate a dimension five Lorentz-violating (LV) nonminimal coupling between the neutral vector meson field strength and the pion current in the context of the Kroll-Lee-Zumino (KLZ) model. In this modified model we study the vector meson dominance (VMD) by means of the imposition of new universality conditions between the couplings that comes from LV contributions. We also show that the LV nonminimal coupling leads to a linear momentum dependence in the timelike pion form factor, that is used to evaluate LV corrections for the muon anomalous magnetic moment. The experimental imprecision of such a quantity allows us to obtain upper bound g¯ξ0<1.0GeV−1. In addition, we also use the LV nonminimal coupling in the KLZ model to recalculate the ρ decay rate. In this case the experimental imprecision is used to constrain the magnitude of the LV parameter at the level of g¯ξ0<1.9×10−2GeV−1.

QCD constituent counting rules for neutral vector mesons

QCD constituent counting rules define the scaling behavior of exclusive hadronic scattering and electromagnetic scattering amplitudes at high momentum transfer in terms of the total number of fundamental constituents in the initial and final states participating in the hard subprocess. The scaling laws reflect the twist of the leading Fock state for each hadron and hence the leading operator that creates the composite state from the vacuum. Thus, the constituent counting scaling laws can be used to identify the twist of exotic hadronic candidates such as tetraquarks and pentaquarks. Effective field theories must consistently implement the scaling rules in order to be consistent with the fundamental theory. Here we examine how one can apply constituent counting rules for the exclusive production of one or two neutral vector mesons $V^0$ in $e^+ e^-$ annihilation, processes in which the $V^0$ can couple via intermediate photons. In case of a (narrow) real $V^0$, the photon virtuality is fixed to a precise value $s_1 = m_{V^0}^2$, in effect treating the $V^0$ as a single fundamental particle. Each real $V^0$ thus contributes to the constituent counting rules with $N_{V_0} = 1$. In effect, the leading operator underlying the $V^0$ has twist 1. Thus, in the specific physical case of single or double on-shell $V^0$ production via intermediate photons, the predicted scaling from counting rules coincides with Vector Meson Dominance (VMD), an effective theory that treats $V^0$ as an elementary field. However, the VMD prediction fails in the general case where the $V^0$ is not coupled through an elementary photon field, and then the leading-twist interpolating operator has twist $N_{V_0} = 2$. Analogous effects appear in $pp$ scattering processes.

QCD compositeness as revealed in exclusive vector boson reactions through double-photon annihilation: e+e−→γγ⁎→γV0 and e+e−→γ⁎γ⁎→V0V0

We study the exclusive double-photon annihilation processes, $e^+ e^- \to \gamma \gamma^\ast\to \gamma V^0$ and $e^+ e^- \to \gamma^\ast \gamma^\ast \to V^0_a V^0_b,$ where the $V^0_i$ is a neutral vector meson produced in the forward kinematical region: $s \gg -t$ and $-t \gg \Lambda_{\rm QCD}^2$. We show how the differential cross sections $\frac{d\sigma}{dt}$, as predicted by QCD, have additional falloff in the momentum transfer squared $t$ due to the QCD compositeness of the hadrons, consistent with the leading-twist fixed-$\theta_{\rm CM} $ scaling laws. However, even though they are exclusive channels and not associated with the conventional electron-positron annihilation process $e^+ e^- \to \gamma^\ast \to q \bar q,$ these total cross sections $\sigma(e^+ e^- \to \gamma V^0) $ and $\sigma(e^+ e^- \to V^0_a V^0_b),$ integrated over the dominant forward- and backward-$\theta_{\rm CM}$ angular domains, scale as $1/s$, and thus contribute to the leading-twist scaling behavior of the ratio $R_{e^+ e^-}$. We generalize these results to exclusive double-electroweak vector-boson annihilation processes accompanied by the forward production of hadrons, such as $e^+ e^- \to Z^0 V^0$ and $e^+ e^- \to W^-\rho^+$. These results can also be applied to the exclusive production of exotic hadrons such as tetraquarks, where the cross-section scaling behavior can reveal their multiquark nature.

The magnetic polarizabilities andg-factor of the neutral and chargedρmesons in a strong magnetic field on the lattice

Study of the ground state energies of neutral and charged vector meson was performed in SU (3) lattice gauge theory in the strong abelian magnetic field. Our method allows us to distinguish the ground state energy of mesons for various spin projections on the axis of the external magnetic field . We are observe the splitting the ground state energy of ρ mesons depending on spin projections: for neutral ρ 0 meson with zero spin projection on the axis of the field ground state energy decreases, while the energies with non-zero spins increase with the field value. For charged ρ ± mesons we observe the agreement between Landau level picture and our data at magnetic field less then 0.6GeV 2 . The magnetic polarizabilities of vector mesons were found for the lattice volume 18 4 fitting the ground state energies. We found the g -factor of ρ ± in the chiral limit. This value is compatible with experimental determination and theoretical value from relativistic quark model.

On vector dominance

We argue that a Regge-pole modification of the VDM puts on equal footing the asymptotic behavior of electromagnetic and neutral vector meson currents.

Magnetic polarizabilities of light mesons in [formula omitted] lattice gauge theory

We investigate the ground state energies of neutral pseudoscalar and vector meson in SU(3) lattice gauge theory in the strong abelian magnetic field. The energy of ρ0 meson with zero spin projection sz=0 on the axis of the external magnetic field decreases, while the energies with non-zero spins sz=−1 and +1 increase with the field. The energy of π0 meson decreases as a function of the magnetic field. We calculate the magnetic polarizabilities of pseudoscalar and vector mesons for lattice volume 184. For ρ0 with spin |sz|=1 and π0 meson the polarizabilities in the continuum limit have been evaluated. We do not observe any evidence in favour of tachyonic mode existence.

Charged and neutral vectorρmesons in a magnetic field

The vector meson $\rho$ in the presence of external magnetic field has been investigated in the framework of the Nambu--Jona-Lasinio model, where mesons are constructed by infinite sum of quark-loop chains by using random phase approximation. The $\rho$ meson polarization function is calculated to the leading order of $1/N_c$ expansion. It is found that the constituent quark mass increases with magnetic field, the masses of the neutral vector meson $\rho^{0}$ with spin component $s_z=0,\,\pm1$ and the charged vector meson $\rho^{\pm}$ with $s_z=0$ also increases with magnetic field. However, the mass square of the charged vector meson $\rho^{+}$ ($\rho^{-}$) with $s_z=+1$ ($s_z=-1$) decreases linearly with magnetic field and drops to zero at the critical magnetic field $e B_c \simeq 0.2 {\rm GeV}^2$, which indicates the possible condensation of charged vector meson in the vacuum. This critical magnetic field is much lower than the value $eB_c=0.6 {\rm GeV}^2$ predicted by a point-like vector meson. We also show that if we use lowest Landau level approximation, the mass of the charged vector meson $\rho^{\pm}$ for $s_z=\pm1$ cannot drop to zero at high magnetic fields.

Vector and axial mesons in strong abelian magnetic field in SU(3) lattice gauge theory

We calculate the correlators of vector and axial currents in external strong abelian magnetic field in SU(3) gluodynamics. From the correlators the masses (ground state energies) of neutral ρ and a 1 and charged ρ mesons have been calculated depending on its spin projection on the axis of external magnetic field. The energies of neutral vector mesons with zero spin decrease, while the energies of neutral vector and axial mesons with nonzero spin increase as a function of the field value. Also we show the splitting of the ground state energy for the charged ρ ± mesons in external magnetic field.

Leptonic decays of vector mesons in a power-law potential model of independent quarks

A relativistic power-law potential model of independent quarks is used to study the leptonic decays of neutral vector mesons. Here, the transition probability amplitude for leptonic decay of meson is determined from the momentum distribution function which is found from the assumption of a strong correlation existing between the momenta of quark and antiquark inside the meson. The model parameters are first determined from the application of the model to study the ground state spectra of ρ, ω, ϕ, ψ and ϒ mesons together with the radiative decay widths of mesons. The same model with no adjustable parameters is then used to evaluate the leptonic decay widths and the electromagnetic decay constants for the vector mesons ρ, ω, ϕ, ψ and ϒ. The calculated results are in remarkable agreement with the corresponding experimental values.

LEPTONIC DECAY WIDTHS OF VECTOR MESONS IN A RELATIVISTIC POTENTIAL MODEL

Leptonic decay widths and the corresponding decay constants of neutral vector mesons are calculated in the framework of a square-root potential model of independent quarks. Starting with the assumption that a strong correlation exists between the momenta of the quark and anti-quark inside the meson so as to have their total momenta identically zero in the center-of-mass frame of the meson, we find the quark and anti-quark momentum distribution amplitude which is used to determine the transition probability amplitude for the leptonic decay of mesons. The calculated results for leptonic decay widths and the electromagnetic decay constants for the vector mesons \rho, \omega, \phi and \psi are in good agrement with the corresponding experimental values. The results for the heavy meson \Upsilon are somewhat lower than the experimental values.

Fractional exclusion statistics applied to relativistic nuclear matter

The effect of statistics of the quasiparticles in the nuclear matter at extreme conditions of density and temperature is evaluated in the relativistic mean-field model generalized to the framework of the fractional exclusion statistics (FES). In the model, the nucleons are described as quasiparticles obeying FES and the model parameters were chosen to reproduce the ground state properties of the isospin-symmetric nuclear matter. In this case, the statistics of the quasiparticles is related to the strengths of the nucleon–nucleon interaction mediated by the neutral scalar and vector meson fields. The relevant thermodynamic quantities were calculated as functions of the nucleons density, temperature and fractional exclusion statistics parameter α. It has been shown that at high temperatures and densities the thermodynamics of the system has a strong dependence on the statistics of the particles. The scenario in which the nucleon–nucleon interaction strength is independent of the statistics of particles was also calculated, but it leads in general to unstable thermodynamics.

Updated search for lepton-flavor-violating tau decays at Belle

Recent updates in the search for lepton-flavor-violating τ decays at the Belle experiment are presented. The Belle detector has successfully accumulated data samples of > 10 9 τ pairs. Using such a large amount of samples, searches for τ decays to a lepton and neutral pseudo-scalar meson or vector meson have been performed. The upper limit of the branching ratio (BR) was obtained to be O ( 10 − 8 ) . The search for τ → μ ρ set the most stringent upper limit ( BR 1.2 × 10 − 8 at the 90% confidence level) among all of the lepton-flavor-violating τ decays.

A covariant investigation of Neutral Vector Mesons: dynamical properties and electromagnetic decay widths

A simple, but fully-covariant model for describing neutral Vector Mesons, in both light and heavy sectors, is briefly illustrated. The main ingredients of our relativistic constituent model are i) an Ansatz for the Bethe-Salpeter vertex for Vector Mesons, and ii) a Mandelstam-like formula for the electromagnetic decay widths. The free parameters of our approach are fixed through a comparison with the valence transverse-momentum distribution, $n(k_\perp)$, obtained within phenomenological Light-Front Hamiltonian Dynamics models reproducing the mass spectra. Preliminary results for the transverse-momentum distributions, the parton distribution and the electromagnetic decay constants are shown.