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Observation of {chi}{sub c1} Decays into Vector Meson Pairs {phi}{phi}, {omega}{omega}, and {omega}{phi}
Using (106{+-}4)x10{sup 6} {psi}(3686) events accumulated with the BESIII detector at the BEPCII e{sup +}e{sup -} collider, we present the first measurement of decays of {chi}{sub c1} to vector meson pairs {phi}{phi}, {omega}{omega}, and {omega}{phi}. The branching fractions are measured to be (4.4{+-}0.3{+-}0.5)x10{sup -4}, (6.0{+-}0.3{+-}0.7)x10{sup -4}, and (2.2{+-}0.6{+-}0.2)x10{sup -5}, for {chi}{sub c1}{yields}{phi}{phi}, {omega}{omega}, and {omega}{phi}, respectively, which indicates that the hadron helicity selection rule is significantly violated in {chi}{sub cJ} decays. In addition, the measurement of {chi}{sub cJ}{yields}{omega}{phi} provides the first indication of the rate of doubly OZI-suppressed {chi}{sub cJ} decay. Finally, we present improved measurements for the branching fractions of {chi}{sub c0} and {chi}{sub c2} to vector meson pairs.
Scalar mesons in a linear sigma model with (axial-)vector mesons
The structure of the scalar mesons has been a subject of debate for many decades. In this work we look for qq states among the physical resonances using an extended Linear Sigma Model that contains scalar, pseudoscalar, vector, and axial-vector mesons both in the non-strange and strange sectors. We perform global fits of meson masses, decay widths and amplitudes in order to ascertain whether the scalar qq states are below or above 1 GeV. We find the scalar states above 1 GeV to be preferred as qq states.
Mass spectrum of vector mesons and their leptonic-decay constants in the bilocal relativistic potential model
A phenomenological model is developed in terms of bilocal meson fields in order to describe a vector meson and its leptonic decays. A new Salpeter equation for this particle and the Schwinger-Dyson equation allowing for the presence of an arbitrary potential and for a modification associated with the renormalization of the quark (antiquark ) wave function within the meson are given. An expression for the constant of the leptonic decay of the charged rho meson is obtained from an analysis of the decay process τ → ρν via parametrizing in it the hadronization of intermediate charged weak W bosons into a bilocal vector meson. The potential is chosen in the form of the sum of harmonic-oscillator and Coulomb potentials, and the respective boundary-value problem is formulated. It is shown that the solutions to this problem describe both the mass spectrum of vector mesons and their leptonic-decay constants.
Relativistic spin dynamics for vector mesons
We propose a relativistic theory for spin density matrices of vector mesons based on Kadanoff-Baym equations in the closed-time-path formalism. The theory puts the calculation of spin observables such as the spin density matrix element ρ 00 for vector mesons on a solid ground. Within the theory we formulate ρ 00 for ϕ mesons into a factorization form in separation of momentum and spacetime variables. We argue that the main contribution to ρ 00 at lower energies should be from the ϕ fields that can polarize the strange quark and antiquark in the same way as electromagnetic fields. The key observation is that there is correlation inside the ϕ meson wave function between the ϕ field that polarizes the strange quark and that polarizes the strange antiquark. This is reflected by the fact that the contributions to ρ 00 are all in squares of fields that are nonvanishing even if the fields may strongly fluctuate in spacetime. The fluctuation of strong force fields can be extracted from ρ 00 of unflavored vector mesons as links to fundamental properties of quantum chromodynamics. Published by the American Physical Society 2024
Measurement of polarization observables in vector meson photoproduction using a transversely-polarized frozen-spin target and polarized photons at CLAS, Jefferson Lab
The study of baryon resonances provides a deeper understanding of the strong interaction because the dynamics and relevant degrees of freedom hidden within them are re ected by the properties of the excited states of baryons. Higher-lying excited states at and above 1.7 GeV/c 2 are generally predicted to have strong couplings to final states involving a heavier meson, e. g. one of the vector mesons, ρ, ω φ, as compared to a lighter pseudoscalar meson, e. g. π and η. Decays to the ππΝ final states via πΔ also become more important through the population of intermediate resonances. We observe that nature invests in mass rather than momentum. The excited states of the nucleon are usually found as broadly overlapping resonances which may decay into a multitude of final states involving mesons and baryons. Polarization observables make it possible to isolate single resonance contributions from other interference terms. The CLAS g9 (FROST) experiment, as part of the N* spectroscopy program at Jefferson Laboratory, accumulated photoproduction data using circularly- & linearly-polarized photons incident on a transversely-polarized butanol target (g9b experiment) in the photon energy range 0:3-2:4 GeV & 0:7-2:1 GeV, respectively. In this work, the analysis of reactions and polarization observables which involve two charged pions, either in the fully exclusive reaction γρ -> ρπ+π- or in the semi-exclusive reaction with a missing neutral pion, γρ -> ρπ + π - (π 0 ) will be presented. For the reaction ρπ + π - , eight polarization observables (I s , I c , P x , P y , $P^s_{x;y}$, $P^c_{x; y}$) have been extracted. The high statistics data rendered it possible to extract these observables in three dimensions. All of them are first-time measurements. The fairly good agreement of Is, Ic obtained from this analysis with the experimental results from a previous CLAS experiment provides support for the first-time measurements. For the reaction γρ -> ρω -> ρπ + π(π 0 , five polarization observables (T, Σ, F, H, P) have been extracted, four of which are first-time measurements at all energies. This analysis thus represents a comprehensive program on vector-meson photoproduction: The ω is observed and studied directly from the data and the polarization observables for the (broad) ω can be extracted from the double-pion reaction in a partial-wave analysis. The 13 polarization observables extracted in this analysis substantially augment the world database of polarization observables for these reactions and are expected to play a crucial role in identifying the contributing baryon resonances.
Measurement of Low Mass Vector Mesons Production and Possible Modification in Heavy Ion Collisions at Forward Rapidity
The data collected over the past decade have demonstrated that the Relativistic Heavy Collider (RHIC) at BNL has created the Quark Gluon Plasma (QGP). A major objective of heavy ion physics nowadays is to study and quantify the fundamental properties of the QGP. One of the crucial probes of this matter is di-lepton measurement in the low mass region. Di-leptons are not affected by the strong interaction once produced; therefore, they can probe the whole evolution of the collision. The planned study will focus on the low mass vector mesons (p, ω, and Φ) through their di-lepton decay channel. The low mass vector mesons are especially good probes to study the properties of this matter created in heavy-ion collisions. Due to their short lifetimes, considerable fraction of them decays inside the hot and dense media. Knowledge of their production rates and spectral properties provides insights into the medium properties; they provide information about in-medium modifications of their spectral shape. The low mass vector mesons also allow understanding the nature of the chiral symmetry restoration in hot and/or dense matter. Generally, there are array of effects due to QGP which can contribute to the modification of the spectra and the true relative contribution is difficult to disentangle. Therefore, studying different colliding systems and wide range of observables at different kinematics will allow disentangling the modification effects and better understand the properties of QGP and the low mass vector mesons will provide very valuable information. In addition, this measurement offers a unique and critical look at QGP where we focus on the low mass vector mesons at forward rapidities which has not been done at RHIC.
Hadronic structure on the light front. VIII. Light scalar and vector mesons
We use the QCD instanton vacuum model to discuss the emergence of the light scalar and vector mesons on the light front. We take into account both the instanton and anti-instanton single and molecular interactions on the light quarks, in the form of nonlocal effective interactions. Although the molecular induced interactions are suppressed by a power of the packing fraction, they are still sufficient to bind the vector mesons, while keeping most of the scalar spectrum relatively unchanged. We explicitly derive the light front distribution amplitudes and partonic functions for the scalar and vector mesons, and compare them after pertinent QCD evolution, to the available empirical and lattice measured counterparts. The Dirac electric form factors for both the pion and ρ meson are derived, and shown to compare well with current data. Published by the American Physical Society 2024
Spin alignment of vector mesons by glasma fields
We explain how spin alignment of vector mesons can be induced by background fields, such as electromagnetic fields or soft gluon fields. Our study is based on the quantum kinetic theory of spinning quarks and antiquarks and incorporates the relaxation of the dynamically generated spin polarization. The spin density matrix of vector mesons is obtained by quark coalescence via the Wigner function and kinetic equation. Our approach predicts a local spin correlation that is distinct from the nonlocal expressions previously obtained in phenomenological derivations. We estimate the magnitude of such local correlations in the glasma model of the preequilibrium phase of relativistic heavy ion collisions. It is found that the resulting spin alignment could be greatly enhanced and may be comparable to the experimental measurement in order of magnitude. We further propose new phenomenological scenarios to qualitatively explain the transverse-momentum and centrality dependence of spin alignment in a self-consistent framework.
Practical considerations for measuring global spin alignment of vector mesons in relativistic heavy ion collisions
Global spin alignment of vector mesons is a sensitive probe of system vorticity and particle production mechanism in relativistic heavy ion collisions. The measurement of global spin alignment is gaining increasing interest and deserves careful considerations. In this paper, we lay out a few practical issues that need to be taken care of when measuring global spin alignment of vector mesons. They are, the correction for event plane resolution, reconciling measurements made with different event planes, the correction for the effect of finite acceptance in pseudorapidity, and the consideration for measuring the azimuthal angle dependence. Furthermore insights and methodologies offered in this paper will help experiments to measure the global spin alignment properly and accurately.
Effects of nuclear structure and quantum interference on diffractive vector meson production in ultra-peripheral nuclear collisions
Here we study diffractive vector meson production in ultra-peripheral collisions (UPCs) of heavy nuclei, utilizing a theoretical framework based on the Color Glass Condensate (CGC) formalism. We focus on Au + Au, U + U, Ru + Ru, Zr + Zr, and Pb + Pb collisions, examining the transverse momentum dependence of vector meson production cross-sections and co s(2ΔΦ)asymmetries in the decay product distributions to explore the role of nuclear geometry. The angular modulation is due to the linear polarization of the incoming photons and quantum interference effects. We extract nuclear radii and find them to be consistent with experimental data from the STAR collaboration. The amplitudes of the cos(2ΔΦ)modulation in the cross-section and the extracted radii depend on the nuclear geometry. This dependence is dominated by the geometry-dependent variation of the minimum impact parameter required for ultra-peripheral collisions.
Low-mass vector-meson production at forward rapidity in 𝑝 + 𝑝 and Au + Au collisions at $\sqrt{𝑠_{𝑁𝑁}}$ = 200 GeV
The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson (𝜔+𝜌 and 𝜙) production through the dimuon decay channel at forward rapidity (1.2 < |y| < 2.2) in 𝑝 + 𝑝 and Au + Au collisions at $\sqrt{𝑠_{𝑁𝑁}}$ = 200 GeV. The low-mass vector-meson yield and nuclear-modification factor were measured as a function of the average number of participating nucleons, ⟨𝑁 part ⟩, and the transverse momentum 𝑝 𝑇 . These results were compared with those obtained via the kaon decay channel in a similar 𝑝 𝑇 range at midrapidity. The nuclear-modification factors in both rapidity regions are consistent within the uncertainties. A comparison of the 𝜔 + 𝜌 and 𝐽/𝜓 mesons reveals that the light and heavy flavors are consistently suppressed across both 𝑝 𝑇 and ⟨𝑁 part ⟩. Finally, in contrast, the 𝜙 meson displays a nuclear-modification factor consistent with unity, suggesting strangeness enhancement in the medium formed.
Current-algebra determination of coupling parameters in vector-meson field theory.
Coupling parameter in vector-meson field theory determined using current algebra, discussing pion and kaon four momenta values for correction factors