Vector Mesons Research Articles

Semileptonic decays D → P/V/Sℓ+νℓ with the SU(3) flavor symmetry/breaking

Many exclusive c→d/sℓ+νℓ(ℓ=e,μ,τ) transitions have been well measured, and they can be used to test the theoretical calculations. Motivated by this, we study the D→P/V/Sℓ+νℓ decays induced by the c→d/sℓ+νℓ transitions with the SU(3) flavor symmetry approach, where P denotes the pseudoscalar meson, V denotes the vector meson, and S denotes the scalar meson with a mass below 1 GeV. The different decay amplitudes of the D→Pℓ+νℓ, D→Vℓ+νℓ or D→Sℓ+νℓ decays can be related by using the SU(3) flavor symmetry and by considering the SU(3) flavor breaking. Using relevant data, we predict the not yet measured or not yet well measured processes in the D→P/V/Sℓ+νℓ decays. We find that the SU(3) flavor symmetry approach works well in the D→P/Vℓ+νℓ decays. Many branching ratios of the D→Sℓ+νℓ decays are predicted by using the data of the Ds+→f0(980)e+νe and D→S(S→P1P2)ℓ+νℓ decays, in addition, the two quark and the four quark scenarios for the light scalar mesons are analyzed. The SU(3) flavor symmetry predictions of the D→Sℓ+νℓ decays need to be further tested, and our predictions of the D→Sℓ+νℓ decays are useful for probing the structure of light scalar mesons. Our results in this work could be used to test the SU(3) flavor symmetry approach in the semileptonic D decays by the future experiments at BESIII, LHCb and BelleII.

Search for charged lepton flavor violation in J/ψ decays at BESIII

The observation of any charged lepton flavor violation (CLFV) process would be a clear signal of new physics beyond the Standard Model. Various decay modes, including lepton (μ, τ) decays, pseudoscalar meson (K,π) decays, vector meson (ϕ, J/ψ, Υ) decays, and Higgs decays, have been explored to detect CLFV. Focusing on the search for CLFV at the τ-charm region, the results of the search for J/ψ → eτ/eμ using the 10 billion J/ψ events collected by the BESIII experiment are presented. The upper limits (ULs) at the 90% confidence level are ℬ(J/ψ → e ± τ ∓) < 7.5 × 10-8 and ℬ(J/ψ → e ± μ ∓) < 4.5 × 10-9, respectively. Improving the previously published limits by two orders of magnitudes, the results are the most stringent CLFV searches in heavy quarkonium system.

Extending StringSpinner to handle vector-meson spin

Quark spin effects in hadronization were recently included in the Pythia 8 Monte Carlo event generator for the simulation of the deep inelastic scattering (DIS) process off a polarized proton or neutron target. The spin effects were activated via the external StringSpinner package, which is based on the string+P03 model of polarized hadronization, and were restricted to the production of pseudoscalar mesons in string fragmentation. The struck quark polarization could either be calculated using parametrizations of the transversity PDFs or be freely specified. In this article we present a major extension of StringSpinner that includes vector meson production in the Pythia 8 string fragmentation. The spin-dependent emission and decay processes of the vector mesons are described using the string+P03 model, which systematically accounts for the quark-spin degree of freedom in the fragmentation chain. The new package works with the version 8.3 of the Pythia event generator and it allows for a more complete and quantitative simulation of the final states in polarized semi-inclusive DIS events. Also, it can be used to study the transverse-spin effects for the production of vector mesons. After describing the new version of StringSpinner, examples of its usage in semi-inclusive DIS events are presented. New version program summaryProgram Title: StringSpinnerCPC Library link to program files:https://doi.org/10.17632/37jrpmyz3t.2Developer's repository link:https://gitlab.com/albikerbizi/stringspinner.gitLicensing provisions: GNU GPL v2 or laterProgramming language:C++, FortranJournal reference of previous version: Comput. Phys. Commun. 272 (2022) 108234.Does the new version supersede the previous version?: YesReasons for the new version: Vector meson emission and decay is required for a more complete simulation of the DIS final states.Summary of revisions: The spin-dependence of the string fragmentation is extended to include the production and the decay of polarized vector mesons.Nature of problem: Vector meson contribute strongly to the final hadrons produced in DIS, and they can produce non-trivial effects on the spin-dependent observables.Solution method: Extend the previous version of StringSpinner to include polarized vector meson production and decay using a more complete model of polarized hadronization.

CP asymmetry from the resonance effect of the B meson decay process with π and K final states* *Supported by the Natural Science Foundation of Henan Province, China (232300420115), and the National Natural Science Foundation of China (12275024).

We present the novel resonance, which generates a strong phase associated with vector meson resonances, leading to significant CP asymmetry in the interference region. The , , and resonances arise from the mixing of the vector mesons ϕ, ρ, and ω. We calculate the CP asymmetry from the decay mode of . Meanwhile, the localized CP asymmetries are presented and a detailed analysis is performed. The CP asymmetry from the decay mode of is also presented in our framework, which is highly consisted with that of the LHC experiment. The introduced CP asymmetry can provide a favorable theoretical support for experimental exploration in the future.

Spin alignment of vector mesons from quark dynamics in a rotating medium* *Supported in part by the National Natural Science Foundation of China (NSFC) (12235016, 12221005), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB34030000), the start-up funding from the University of Chinese Academy of Sciences (UCAS), and the Fundamental Research Funds for the Central Universities

Vorticities in heavy-ion collisions (HICs) are supposed to induce spin alignment and polarization phenomena of quarks and mesons. In this work, we analyze the spin alignment of vector mesons ϕ and ρ induced by rotation from quark dynamics in the framework of the Nambu-Jona-Lasinio (NJL) model. The rotating angular velocity induces mass splitting of spin components for vector mesons . This behavior contributes to the spin alignment of vector mesons in an equilibrium medium and naturally explains the negative deviation of for vector mesons. Incidentally, the positive deviation of under the magnetic field can also be easily understood from quark dynamics.

Multiscale Imaging of Nuclear Deformation at the Electron-Ion Collider.

We show within the color glass condensate framework that exclusive vector meson production at high energy is very sensitive to the geometric deformation of the target nucleus at multiple length scales. We show that different multipole deformation parameters affect different regions of transverse momentum transfer. These results have two important consequences: (1)Deformations of nuclear targets need to be taken into account when making predictions for and interpreting certain observables at the EIC. (2)Differential diffractive vector meson production has the potential to become a powerful tool, enabling the most direct measurements of nuclear structure at different length scales, ranging from large scale nuclear deformation at low transverse momentum transfer to fluctuations on nucleon- and subnucleon-size scales at higher transverse momentum transfer.

Predicting the exclusive diffractive electron-ion cross section at small x with machine learning in Sartre

The event generator Sartre has been used extensively for simulations of electron-ion collisions in preparation for the Electron-Ion Collider (EIC). Sartre simulates exclusive diffraction in eA collisions, in principle for any nuclear species and exclusive final state, usually a vector meson. The coherent and incoherent cross sections for each process are calculated in the colour dipole model for small x from the first and second moments of the respective amplitude, averaged over initial state spatial configurations. Taking these averages is a very CPU demanding task. In order to function as an efficient event generator, these amplitude moments are saved into lookup tables which are used as input for the event generation, making the latter a very fast process. However, there are many recent and ongoing developments of the dipole models underlying the calculations, both in terms of fits of the model parameters to new data as well as new parametrisations of the dipole or proton geometries. Therefore, it is desirable to have a more flexible method for producing the lookup tables. Here, we propose a method using neural networks which can reduce the table production time by 90% while retaining the same precision in the resulting cross sections.

Spin alignment of vector mesons by glasma fields

Spin alignment of vector mesons by glasma fields

Revealing the inner structure of the newly observed η 1(1855) via photoproduction

Very recently, a new hadronic exotic state η 1(1855) at the invariant mass spectrum of was observed by the BESIII Collaboration. According to its properties, such as the mass and decay width, the η 1(1855) have been suggested to be a compact multi-quark state, a hadron molecule, or a hybrid meson. In order to distinguish the various interpretations of the η 1(1855), a Reggeized model combined with the vector dominance model for η 1(1855) photoproduction on the proton target is presented. The η 1(1855) photoproduction is dominated by the t-channel vector mesons ρ, ω, and ϕ exchange. If the η 1(1855) is a hybrid meson, the Primakoff effect also should be included. Our calculations show that the total cross section of the η 1(1855) production via γ p reaction can reach up to 0.276 pb for θ = 15° or 0.119 pb for θ = 0°, about 0.0297% or 0.0128% of the total cross section obtained by considering the η 1(1855) as an S-wave molecule. We also find their line shapes are sizably different. If the η 1(1855) is a molecular state, the photoproduction of η 1(1855) near the threshold offers a nice place to test its molecular nature. However, it should be better to take high energy, at least above E γ = 16.97 GeV, to observe the production of η 1(1855) if η 1(1855) is a hybrid meson. These results can be measured in the GlueX experiment or electron-ion collider in China to test the nature of the η 1(1855).

Spin Alignment of Vector Mesons in Heavy-Ion Collisions.

Polarized quarks and antiquarks in high-energy heavy-ion collisions can lead to the spin alignment of vector mesons formed by quark coalescence. Using the relativistic spin Boltzmann equation for vector mesons derived from Kadanoff-Baym equations with an effective quark-meson model for strong interaction and quark coalescence model for hadronizaton, we calculate the spin density matrix element ρ_{00} for ϕ mesons and show that anisotropies of local field correlations with respect to the spin quantization direction lead to ϕ meson's spin alignment. We propose that the local correlation or fluctuation of ϕ fields is the dominant mechanism for the observed ϕ meson's spin alignment and its strength can be extracted from experimental data as functions of collision energies. The calculated transverse momentum dependence of ρ_{00} agrees with STAR's data. We further predict the azimuthal angle dependence of ρ_{00} which can be tested in future experiments.

From Ds → γ in lattice QCD to Bs → μμγ at high q2

We use a recent lattice determination of the vector and axial Ds → γ form factors at high squared momentum transfer q2 to infer their Bs → γ counterparts. To this end, we introduce a phenomenological approach summarized as follows. First, we describe the lattice data with different fit templates motivated by vector-meson dominance, that is expected to hold in the high-q2 region considered. We identify reference fit ansaetze with one or two physical poles, that we validate against alternative templates. Then, the pole residues can be unambiguously related to the appropriate couplings involving the pseudoscalar, the vector mesons concerned, and the photon — or tri-couplings — and the latter can be expressed as sums over quark magnetic moments, weighed by their e.m. charges. This description obeys a well-defined heavy-quark scaling, that allows to parametrically scale up the form factors to the Bs → γ case. We discuss a number of cross-checks of the whole approach, whose validation rests ultimately in a first-principle determination, e.g. in lattice QCD. Finally, we use our obtained form factors to reassess the SM prediction of ℬ(Bs → μ+μ−γ) in the range sqrt{q^2}in [4.2, 5.0] GeV, where an experimental measurement is awaited.

Experimental Study of In-medium Spectral Change of Vector Mesons at J-PARC

Chiral symmetry and its spontaneous breaking is an essential property of the QCD vacuum and is closely related to the generation of hadron mass. J-PARC E16 experiment measures dielectron spectra in p+A collisions at 30 GeV to study the in-medium spectral change of vector mesons that signals the partial restoration of the broken symmetry. The experiment uses the primary proton beam available at the high-momentum beam line of the J-PARC hadron experimental facility. We performed three proton-beam runs intended for beamline and detector commissioning. We are preparing for the next commissioning run in 2023 and the first physics run. We present the experimental setup, some of the expected results, preparation status, and some findings in the commissioning runs.

An Assessment of Pseudoscalar and Vector Meson Electromagnetic Form Factors

An Assessment of Pseudoscalar and Vector Meson Electromagnetic Form Factors

Leptonic Decay Widths for the Composite System of Two Relativistic Fermions

The new relativistic semiclassical leptonic decay widths of vector mesons as the relativistic systems of two quarks with arbitrary masses interacting by means of the funnel-type potentials with Coulomb interaction are obtained. The behavior of the relativistic leptonic decay widths of vector mesons is investigated. Comparison of the behavior for new expression with its relativistic spinless analog is given. Consideration is conducted within the framework of completely covariant quasipotential approach in the Hamiltonian formulation of quantum field theory via a transition to the relativistic configurational representation in the case of two relativistic spin particles of arbitrary masses.

Exclusive photo- and electroproduction of excited light vector mesons via holographic model

In this paper, we study total and differential observables of electro- and photoproduction of light rho , omega and phi mesons as functions of the center-of-mass energy of the gamma p collision and momentum transfer squared |t|. The corresponding vector mesons wave functions have been computed in the framework of relativistic AdS/QCD holographic approach. A satisfactory description of all available data on ground-state rho (1S), omega (1S) and phi (1S) mesons production cross sections has been achieved in the color dipole picture. Finally, the key observables of excited rho (2S), omega (2S) and phi (2S) states production in gamma ^{(*)} p collisions have been presented here using a common wave function formalism. This study reveals a large theoretical uncertainty coming from the modeling of the partial dipole amplitude in the nonperturbative kinematical domain. Hence, the latter could benefit from future measurements of photoproduction of the excited states.

Dark vector mesons at LHC forward detector searches

Confining gauge dynamics in a dark sector is promising to provide dark matter with a mass in the range of sub-GeV to GeV. Such dark sectors consist of composite particles such as dark baryons and dark mesons, that are neutral under the standard-model charge. A dark photon is introduced as a portal matter between the dark sector and the standard-model sector to alleviate cosmological problems (e.g., to maintain kinetic equilibrium between two sectors or to reduce the light dark-sector particles contributing to the dark radiation), and dark hadrons are produced through the same dark photon at accelerator-based experiments. As dark vector mesons and dark pions have similar masses, dark vector mesons can be long-lived particles, which will be explored by far-detector experiments. We study the future prospects of the LHC forward-detector experiments, FASER/FASER2 and FACET, for exploring the dark vector mesons. When the dark photon is heavier than the dark pions, the LHC forward-detector searches will be comparable to DarkQuest, and the invisible decay searches of dark photons will also explore the same parameter space. Meanwhile, when dark photons are lightest in the dark sector, their future prospects will be comparable to the visible decay searches for dark photons at LHCb, Belle-II, and HPS.

Search for lepton-flavor-violating τ decays into a lepton and a vector meson using the full Belle data sample

Charged-lepton-flavor-violation is predicted in several new physics scenarios. We update the analysis of τ lepton decays into a light charged lepton (ℓ = e± or μ±) and a vector meson (V0 = ρ0, ϕ, ω, K*0, or overline{K} *0) using 980 fb−1 of data collected with the Belle detector at the KEKB collider. No significant excess of such signal events is observed, and thus 90% credibility level upper limits are set on the τ → ℓV0 branching fractions in the range of (1.7–4.3) × 10−8. These limits are improved by 30% on average from the previous results.

Collins and Sivers transverse-spin asymmetries in inclusive muoproduction of ρ0 mesons

The production of vector mesons in deep inelastic scattering is an interesting yet scarcely explored channel to study the transverse spin structure of the nucleon and the spin-dependence of fragmentation. The COMPASS collaboration has performed the first measurement of the Collins and Sivers asymmetries for inclusively produced ρ0 mesons. The analysis is based on the data set collected in deep inelastic scattering in 2010 using a 160GeV/cμ+ beam impinging on a transversely polarized NH3 target. The ρ0 mesons are selected from oppositely charged hadron pairs, and the asymmetries are extracted as a function of the Bjorken-x variable, the transverse momentum of the pair and the fraction of the energy z carried by the pair. Indications for positive Collins and Sivers asymmetries are observed.

Cornering large-Nc QCD with positivity bounds

The simple analytic structure of meson scattering amplitudes in the large-Nc limit, combined with positivity of the spectral density, provides precise predictions on low-energy observables. Building upon previous studies, we explore the allowed regions of chiral Lagrangian parameters and meson couplings to pions. We reveal a structure of kinks at all orders in the chiral expansion and develop analytical tools to show that kinks always correspond to amplitudes with a single light pole. We build (scalar- and vector-less) deformations of the Lovelace-Shapiro and Coon UV-complete amplitudes, and show that they lie close to the boundaries. Moreover, constraints from crossing-symmetry imply that meson couplings to pions become smaller as their spin increases, providing an explanation for the success of Vector Meson Dominance and holographic QCD. We study how these conclusions depend on assumptions about the high-energy behavior of amplitudes. Finally, we emphasize the complementarity between our results and Lattice computations in the exploration of large-Nc QCD.

Neutron star properties in the (axial)vector meson extended linear sigma model

AbstractThe equation of state provided by effective models of strongly interacting matter should comply with the restrictions imposed by current astrophysical observations on compact stars. We explore the possibility, that there is quark matter in the center of neutron stars. For the equation of state of the neutron star matter, we use a relativistic mean field model for the hadronic one and the (axial‐)vector meson extended linear sigma model for the quark phase. We assume that the transition is a cross‐over between these phases. We connect the two branches in this cross‐over regime continuously by a polynomial. This equation of state should comply with the restrictions imposed by current astrophysical observations on compact stars. Our model has four free parameters that should be fitted to experimental data. By using a Bayesian analysis, we found that our model could explain all the experimental constraints; furthermore, we have obtained the most probable parameter set for our model.