Properties Of Vector Mesons Research Articles

In-medium properties of the light and heavy-light mesons in a light-front quark model

We investigate the in-medium properties of pseudoscalar and vector mesons with the light-light and heavy-light quarks in a light-front quark model, using the in-medium quark properties computed by the quark-meson coupling model. Both models are constructed on an equal footing with the constituent quark degree of freedom. Here, we particularly focus on the weak decay constants and distribution amplitudes (DAs) of the mesons in symmetric nuclear matter. We find that the weak decay constants decrease as nuclear density increases for $\ensuremath{\pi}$, $K$, $D$, and $B$ pseudoscalar as well as $\ensuremath{\rho}$, ${K}^{*}$, ${D}^{*}$, and ${B}^{*}$ vector mesons, where their properties in free space have good agreement with the available experimental and lattice QCD data. A larger reduction is found for the light-light quark pseudoscalar mesons, while a smaller reduction is found for the heavy-light quark vector mesons, in particular, with the bottom quark. We discuss the effect of the vector potential on the weak decay constants, and present our predictions for the in-medium modifications of DAs. Also, a comparison with the free space lattice QCD data is made.

QCD phase diagram with a background magnetic field in an improved soft-wall AdS/QCD model

We studied the magnetic effects on the chiral transition and the melting properties of vector and axial-vector mesons in the improved soft-wall AdS/QCD model under a charged magnetic background, which is solved perturbatively from an Einstein–Maxwell system with a negative cosmological constant. The phase diagrams for both chiral transition and meson melting have been obtained. We show that the inverse magnetic catalysis emerged naturally in the improved soft-wall model. We also find that the magnetic field can induce meson melting, at least for the vector and axial-vector mesons, in our holographic setup.

Elastic electromagnetic form factors of vector mesons

A symmetry-preserving approach to the two valence-body continuum bound-state problem is used to calculate the elastic electromagnetic form factors of the $\rho$-meson and subsequently to study the evolution of vector-meson form factors with current-quark mass. To facilitate a range of additional comparisons, $K^\ast$ form factors are also computed. The analysis reveals that: vector mesons are larger than pseudoscalar mesons; composite vector mesons are non-spherical, with magnetic and quadrupole moments that deviate $\sim 30$\% from point-particle values; in many ways, vector-meson properties are as much influenced by emergent mass as those of pseudoscalars; and vector meson electric form factors possess a zero at spacelike momentum transfer. Qualitative similarities between the electric form factors of the $\rho$ and the proton, $G_E^p$, are used to argue that the character of emergent mass in the Standard Model can force a zero in $G_E^p$. Morover, the existence of a zero in vector meson electric form factors entails that a single-pole vector meson dominance model can only be of limited use in estimating properties of off-shell vector mesons, providing poor guidance for systems in which the Higgs-mechanism of mass generation is dominant.

Properties of vector and axial-vector mesons in a nonlocal SU(2) PNJL model

We study the features of a SU(2) Polyakov-Nambu-Jona-Lasinio model that includes wave function renormalization and nonlocal vector interactions. Within this framework we analyze, among other properties, the masses, width and decay constants of light vector and axial-vector mesons at finite temperature. Then we obtain the corresponding phase diagram in a finite density scenario, after characterizing the deconfinement and chiral restoration transitions.

Determination of the properties of vector mesons in external magnetic field by quenched SU(3) lattice QCD

We investigate the ground state energies of vector ρ± and K±∗ mesons depending on the magnetic field value in the SU(3) lattice gauge theory. It has been shown that the energy of a vector particle depends on its spin projection on the field axis. The magnetic dipole polarizability and hyperpolarizabilities give significant contributions to the energy value which prevents the formation of the charged vector meson condensate at high magnetic fields. We calculate the g-factor of ρ± and K±∗ mesons and the dipole magnetic polarizability of ρ± mesons.

Hadrons in Nuclear Matter

We review the achievements of the project B.5 , that deals with the calculation of in-medium properties of vector mesons and an analysis of their experimental signals, with a particular emphasis on the ω photoproduction data from CBELSA/TAPS. Other topics addressed include color transparency, pion electroproduction on nucleons, the Primakoff effect for nuclear targets and studies of hadronization at the EIC.

Properties of vector mesons in four pseudoscalars electroproduction

Vector mesons and the W gauge boson share some common features, such as the spin and a very short lifetime. The electromagnetic properties of the W are linked to its gauge nature and thus a big effort has been devoted to measure them, while accounting for its instability. In this work, we elaborate on how these ideas can be translated to study vector mesons. We focus in the unstable property of such states and the restrictions from electromagnetic gauge invariance, describing the differences and similarities. Then, we describe the four pseudoscalars electroproduction as an analog to the e+e-→4fermions process, used to study the electromagnetic properties of the W boson. We point out that the current experimental capabilities are reaching the possibility to measure the magnetic dipole moment of light vector mesons.

Heavy vector and axial-vector mesons in hot and dense asymmetric strange hadronic matter

We calculate the effects of finite density and temperature of isospin asymmetric strange hadronic matter, for different strangeness fractions, on the in-medium properties of vector $\left( D^{\ast}, D_{s}^{\ast}, B^{\ast}, B_{s}^{\ast}\right)$ and axial-vector $\left( D_{1}, D_{1s}, B_{1}, B_{1s}\right)$ mesons, using chiral hadronic SU(3) model and QCD sum rules. We focus on the evaluation of in-medium mass-shift and shift in decay constant of above vector and axial-vector mesons. In QCD sum rule approach, the properties, e.g., the masses and decay constants of vector and axial-vector mesons are written in terms of quark and gluon condensates. These quark and gluon condensates are evaluated in the present work within chiral SU(3) model, through the medium modification of, scalar-isoscalar fields $\sigma$ and $\zeta$, the scalar-isovector field $\delta$ and scalar dilaton field $\chi$, in the strange hadronic medium which includes both nucleons as well as hyperons. As we shall see in detail, the masses and decay constants of heavy vector and axial-vector mesons are affected significantly due to isospin asymmetry and strangeness fraction of the medium and these modifications may influence the experimental observables produced in heavy ion collision experiments. The results of present investigations of in-medium properties of vector and axial-vector mesons at finite density and temperature of strange hadronic medium may be helpful for understanding the experimental data from heavy-ion collision experiments in-particular for the Compressed Baryonic Matter (CBM) experiment of FAIR facility at GSI, Germany.

S= −1 meson-baryon interaction in hot and dense nuclear matter: chiral symmetry, many-body and unitarization for a road to GSI/FAIR

The dynamics of strange pseudoscalar and vector mesons in hot and dense nuclear matter is studied within a chiral unitary framework in coupled channels. Our results set up the starting point for implementations in microscopic transport approaches of heavy-ion collisions, particularly at the conditions of the forthcoming experiments at GSI/FAIR and NICA-Dubna. In the K̄ N sector we focus on the calculation of (off-shell) transition rates for the most relevant binary reactions involved in strangeness production close to threshold energies, with special attention to the excitation of sub-threshold hyperon resonances and isospin effects (e.g. K̄ p vs K̄ n). We also give an overview of recent theoretical developments regarding the dynamics of strange vector mesons (K*, K̄* and ϕ) in the nuclear medium, in connection with experimental activity from heavy-ion collisions and nuclear production reactions. We emphasize the role of hadronic decay modes and the excitation of hyperon resonances as the driving mechanisms modifying the properties of vector mesons.

Dielectron production in 200 GeV p+p and Au+Au collisions at STAR

Leptons do not interact strongly with the hot dense medium created in relativistic heavy ion collisions. They can escape the interaction region undistorted and thus carry direct information about the space-time evolution of the expanding system. In the low mass region (LMR, 0.3 < Mee < 1.1 GeV/c2), dielectron mass spectra can provide the in-medium vector meson properties, while in the intermediate mass region (IMR, 1.1 < Mee < 3 GeV/c2), the slope of dielectron transverse mass spectra is expected to have connection with the QGP temperature.In this paper, we present the centrality and pT dependence of the dielectron mass spectra measured in STAR experiment at RHIC. The data sets used in the analysis include large statistics samples collected during years 2010 for 200 GeV Au+Au collisions and 2012 for 200 GeV p+p collisions. In order to extract underlying physics, we will compare our results with model calculations.

Properties of strange vector mesons in dense and hot matter

We investigate the in-medium properties of strange vector mesons ($K^*$ and $\bar K^*$) in dense and hot nuclear matter based on chirally motivated models of the meson selfenergies. We parameterise medium effects as density or temperature dependent effective masses and widths, obtain the vector meson spectral functions within a Breit-Wigner prescription (as often used in transport simulations) and study whether such an approach can retain the essential features of full microscopic calculations. For $\mu_B\ne 0$ the medium corrections arise from $\bar K^* (K^*) N$ scattering and the $\bar K^* (K^*) \to \bar K (K) \pi$ decay mode (accounting for in-medium $\bar K (K)$ dynamics). We calculate the scattering contribution to the $K^*$ selfenergy based on the hidden local symmetry formalism for vector meson nucleon interactions, whereas for the $\bar K^*$ selfenergy we implement recent results from a selfconsistent coupled-channel determination within the same approach. For $\mu_B\simeq 0$ and finite temperature we rely on a phenomenological approach for the kaon selfenergy in a hot pionic medium consistent with chiral symmetry, and evaluate the $\bar K^* (K^*) \to \bar K (K) \pi$ decay width. The emergence of a mass shift at finite temperature is studied with a dispersion relation over the imaginary part of the vector meson selfenergy.

Improved sum rules for light mesons and thermal hadronic threshold

The thermal properties of light vector and scalar mesons are investigated in the framework of QCD sum rules. The phenomenological side of the correlation function can be calculated using either the quark-hadron duality approach or in terms of two-pion continuum contributions. In the quark-hadron duality approach, a free parameter (hadronic threshold) arises in the phenomenological part and it is necessary to know the temperature dependence of the hadronic threshold. A comparison of above mentioned approaches gives us additional information about the temperature dependence of the hadronic threshold. Taking into account the thermal spectral density and additional operators appearing at finite temperature the thermal QCD sum rules are improved. The decay constants of ρ and σ mesons are calculated and our investigations show that the above mentioned methods give us the same results.

πandρmesons, and their diquark partners, from a contact interaction

We present a unified Dyson-Schwinger equation treatment of static and electromagnetic properties of pseudoscalar and vector mesons, and scalar and axial-vector diquark correlations, based upon a vector-vector contact-interaction. A basic motivation for this study is the need to document a comparison between the electromagnetic form factors of mesons and those diquarks which play a material role in nucleon structure. This is an important step toward a unified description of meson and baryon form factors based on a single interaction. A notable result, therefore, is the large degree of similarity between related meson and diquark form factors. The simplicity of the interaction enables computation of the form factors at arbitrarily-large spacelike-Q^2, which enables us to expose a zero in the rho-meson electric form factor at z_Q^\rho ~ Sqrt[6] m_\rho. Notably, r_\rho*z_Q^\rho ~ r_D*z_Q^D, where r_\rho, r_D are, respectively, the electric radii of the rho-meson and deuteron.

Hadrons in Medium

We review the current status of theories and experiments aiming at an understanding and a determination of the properties of light vector and scalar mesons inside strongly interacting hadronic matter, with an emphasis on linking calculated properties of hadrons in medium to actual observables.

Hadron Properties in Nuclear Matter and the Phase Structure of a Skyrmionic System

Hadron properties and their interactions in a nuclear environment are considered in the framework of the in-medium modified Skyrme model. Furthermore, the influence of the medium modifications of the single hadron properties and their interactions to the stability of the whole system is considered by using the variational method of the Hartree-Fock type. In addition to previous studies, we discuss the possible in-medium modifications of the stabilizing Skyrme term which can be related to the modifications of vector meson properties in a nuclear environment.

HADRONS IN STRONGLY INTERACTING MATTER

We review the current status of theories and experiments aiming at an understanding and a determination of the properties of light vector and scalar mesons inside strongly interacting hadronic matter. Starting from a discussion of the relevant symmetries of QCD and their connection with the hadronic description through QCD sum rules we then discuss hadronic models used to calculate the in-medium self-energies of hadrons and their spectral functions. The difficulties to link these calculated properties to actual observables are emphasized. Finally, we review in detail all the running experiments searching for in-medium changes of vector and scalar mesons, both with relativistic heavy-ion reactions as well as with elementary reactions on (cold) nuclei. Inconsistencies among experimental results are discussed. While almost all experiments observe a considerable broadening of vector mesons inside the nuclear medium, no evidence for mass changes is observed in the majority of the experiments.

Medium Modifications of Light Vector Mesons in Nuclei

There is tremendous interest both experimentally and theoretically in possible modification of the properties of vector mesons, such as a shift in their masses and/or broadening of their widths in dense nuclear matter. These effects can be related to partial restoration of chiral symmetry at high density or temperature. The light vector mesons ( ρ, ω, and ϕ) were photo-produced on 2H, C, Ti, Fe, and Pb targets at the Thomas Jefferson National Laboratory using the CEBAF Large Acceptance Spectrometer (CLAS). The properties of the ρ vector meson at normal nuclear densities and zero temperature were investigated via their rare leptonic decay to e + e − . The rho meson mass distributions were extracted for each of the targets. With respect to the ρ-meson mass, we obtain a small shift compatible with zero. Also, we measure widths consistent with standard nuclear many-body effects such as collisional broadening and Fermi motion.

PHENIX experiment: Recent results

An overview of the latest physics results obtained in the PHENIX experiment by studying pp, dAu, and AuAu interactions at √sNN = 200 GeV is given. Results of measurements of nuclear-modification factors, direct-photon production, and properties of light vector mesons and particles containing heavy c and b quarks are presented. These results are used to deduce information about the properties of dense parton matter produced in collisions of relativistic heavy nuclei at the Relativistic Heavy Ion Collider (RHIC).

MEDIUM MODIFICATIONS OF LIGHT VECTOR MESONS IN PHOTOPRODUCTION REACTIONS AT JLAB

Theoretical calculations predict the modification of properties of vector mesons, such as a shift in their masses and/or broadening of their widths in dense nuclear matter. These effects can be related to partial restoration of chiral symmetry at high density or temperature. The light vector mesons (ρ, ω, and ϕ) were photo-produced on 2 H , C , Ti , Fe , and Pb targets at the Thomas Jefferson National Laboratory using the CEBAF Large Acceptance Spectrometer (CLAS). The data were taken with a beam of tagged photons with energies up to 4 GeV. The properties of the ρ vector meson at normal nuclear densities and zero temperature,were investigated via their rare leptonic decay to e+e-. This decay channel is preferred over hadronic modes in order to eliminate final state interactions in the nuclear matter. A combinatorial background was subtracted from the invariant mass spectra using a well-established event-mixing technique. The ρ meson mass spectrum was extracted after the ω and ϕ signals were removed in a nearly model-independent way. The rho meson mass distributions were extracted for each of the targets. Comparisons were made between the ρ mass spectra from the heavy targets ( A &gt; 2) with the mass spectrum extracted from the deuterium target. With respect to the ρ-meson mass, we obtain a small shift compatible with zero. Also, we measure widths consistent with standard nuclear many-body effects such as collisional broadening and Fermi motion. In this experiment, due to the long lifetimes and momenta greater than 0.8 GeV, the ω and ϕ mesons have a high probability of decaying outside the nucleus in their vacuum state. However, their in-medium widths can be accessed through their absorption inside the nucleus. Preliminary results on the ratios of the nuclear transparencies of the ω and ϕ mesons as a function of the number of target nucleons A, have been obtained and indicate a substantial widening in the medium.

Medium modifications of light vector mesons in photoproduction reactions at JLab

Theoretical calculations predict the modification of properties of vector mesons, such as a shift in their masses and/or broadening of their widths in dense nuclear matter. These effects can be related to partial restoration of chiral symmetry at high density or temperature. Photoproduction of vector mesons off nuclei were performed at Jefferson Lab using the CEBAF Large Acceptance Spectrometer. The data were taken with a beam of tagged photons with energies up to 4 GeV on various nuclear targets. The properties of the ρ vector mesons were investigated via their rare leptonic decay to e+e−. This decay channel is preferred over hadronic modes in order to eliminate final state interactions in the nuclear matter. The combinatorial background in the mass spectrum was removed by a self-normalizing mixed-event technique. The ρ meson mass distributions were extracted for each of the targets. Statistically significant results regarding medium modification of the ρ meson in the nuclear medium rule out large medium effects. Transparency studies of the ω and ϕ vector mesons allow a determination of their widths in the medium.