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Register a new userExclusive production of vector mesons $rho, rho$ and $rho$ by real and virtual photons
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Authors
G.Kulzinger
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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.
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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.
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 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.
We calculate cross sections for the exclusive diffractive leptoproduction of $rho$-mesons, $gamma^*~p~to~rho~p$, within the framework of high-energy factorization. Cross sections for longitudinally and transversally polarized mesons are shown. We employ a wide variety of unintegrated gluon distributions available in the literature and compare to HERA data. The resulting cross sections strongly depend on the choice of unintegrated gluon distribution. We also present predictions for the proton target in the kinematics of the Brookhaven EIC.
Exclusive emissions of vector mesons in forward directions of rapidity offer us a faultless chance to probe the proton structure at small-$x$. A high-energy factorization formula is established within BFKL, given as the convolution of an impact factor depicting the forward-meson emission and of an unintegrated gluon distribution (UGD) driving the gluon evolution at small-$x$. As a nonperturbative quantity, the UGD is not well known and several models for it exist. We present recent progresses on the study of the exclusive forward $rho$-meson leptoproduction at HERA and EIC energies, showing how osbervables sensitive to different polarization states of the $rho$-particle act as discriminators for the existing UGD models.
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