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Register a new userVector mesons $rho, rho$ and $rho$ diffractively photo- and leptoproduced
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G.Kulzinger
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In the framework of non-perturbative QCD we calculate high-energy diffractive production of vector mesons $rh, rh$ and $rh$ by real and virtual photons on a nucleon. The initial photon dissociates into a $qbar{q}$-dipole and transforms into a vector meson by scattering off the nucleon which, for simplicity, is represented as quark-diquark. The relevant dipole-dipole scattering amplitude is provided by the non-perturbative model of the stochastic QCD vacuum. The wave functions result from considerations in the frame of light-front dynamics; the physical $rh$- and $rh$-mesons are assumed to be mixed states of an active 2S-excitation and some residual rest (2D- and/or hybrid state). We obtain good agreement with the experimental data and get an understanding of the markedly different $pi^+pi^-$-mass spectra for photoproduction and $e^+e^-$-annihilation.
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We calculate diffractive photo- and leptoproduction of $rho$-, $rho$- and $rho$-mesons. The incoming photon dissociates into a $qbar{q}$-dipole which scatters on the nucleon and transforms into a vector meson state. The scattering amplitude is calculated in non-perturbative QCD with the model of the stochastic vacuum. Assuming that the physical $rho$- and $rho$-mesons are mixed states of an active 2S-excitation and some residual hybrid state which cannot be produced diffractively in lowest order QCD, we obtain good agreement with the data, especially the markedly different spectrum in the $pi^+pi^-$-invariant mass for photoproduction and $e^+e^-$-annihilation.
We present a non-perturbative QCD calculation of high-energy diffractive photo- and leptoproduction of vector mesons $rho$, $rho$ and $rho$ on a nucleon. The initial photon splits up in a $qbar{q}$-dipole and transforms into a vector meson by scattering on the quark-diquark nucleon. The dipole-dipole scattering amplitude is provided by the non-perturbative model of the stochastic QCD vacuum, the wave functions result from considerations on the light-cone. We assume the physical $rho$- and $rho$-states to be mixed states of an active 2S-excitation and a rest whose coupling to the photon is suppressed. We obtain good agreement with the experimental data and get an understanding of the markedly different spectrum in the $pi^+pi^-$-invariant mass for photoproduction and $e^+e^-$-annihilation.
We compute the difference in decay widths of charged and neutral rho(770) vector mesons. The isospin breaking arising from mass differences of neutral and charged pi and rho mesons, radiative corrections to rho -> pipi, and the rho -> pipigamma decays are taken into account. It is found that the width difference Delta Gamma_rho is very sensitive ot the isospin breaking in the $rho$ meson mass Delta m_rho. This result can be useful to test the correlations observed between the values of these parameters extracted from experimental data.
Using interpolators with different SU(2)_L times SU(2)_R transformation properties we study the chiral symmetry and spin contents of the rho- and rho-mesons in lattice simulations with dynamical quarks. A ratio of couplings of the $qbargamma^i{tau}q$ and $qbarsigma^{0i}{tau}q$ interpolators to a given meson state at different resolution scales tells one about the degree of chiral symmetry breaking in the meson wave function at these scales. Using a Gaussian gauge invariant smearing of the quark fields in the interpolators, we are able to extract the chiral content of mesons up to the infrared resolution of ~1 fm. In the ground state rho meson the chiral symmetry is strongly broken with comparable contributions of both the (0,1) + (1,0) and (1/2,1/2)_b chiral representations with the former being the leading contribution. In contrast, in the rho meson the degree of chiral symmetry breaking is manifestly smaller and the leading representation is (1/2,1/2)_b. Using a unitary transformation from the chiral basis to the {2S +1}L_J basis, we are able to define and measure the angular momentum content of mesons in the rest frame. This definition is different from the traditional one which uses parton distributions in the infinite momentum frame. The rho meson is practically a 3S_1 state with no obvious trace of a spin crisis. The rho meson has a sizeable contribution of the 3D_1 wave, which implies that the rho meson cannot be considered as a pure radial excitation of the rho meson.
The DDrho form factor is evaluated in a QCD sum rule calculation for both D and rho off-shell mesons. We study the double Borel sum rule for the three point function of two pseudoscalar and one vector meson currents. We find that the momentum dependence of the form factors is very different if the D or the rho meson is off-shell, but they lead to the same coupling constant in the DDrho vertex. We discuss two different approaches to extract the DDrho coupling constant.
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