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D. I. Melikhov

Publications and source records attributed to D. I. Melikhov.

3 recordsLinked to original sources
arXiv1999

Pomeron in diffractive processes $γ^*(Q^2)p\toρ^0 p$ and $γ^*(Q^2)p\toγ^*(Q^2) p$ at large Q^2: the onset of pQCD

We study the reactions $γ^*(Q^2)p\toρ^0 p$ and $γ^*(Q^2)p\toγ^*(Q^2) p$ at large Q^2 and $W^2/Q^2$ and small momentum transfer, $κ^2_\perp$, to the nucleon where the pomeron exchange dominates. At large Q^2 the virtual photon selects a hard $q\bar q$ pair, thus selecting the hard pomeron component (the BFKL pomeron). The amplitudes for both transverse and longitudinal polarizations of the initial photon and outgoing $ρ$-meson (photon) are calculated in the framework of the BFKL pomeron exchange. Our calculations show that one cannot expect the early onset of the pure perturbative regime in the discussed diffractive processes: the small interquark distances, $ρ_{q\bar q} <0.2$ fm, start to dominate not earlier than at $Q^2 \simeq 100 GeV^2, W^2/Q^2 \simeq 10^7$ in $γ^*(Q^2)p\toρ^0 p$ and $Q^2 \simeq 50 GeV^2, W^2/Q^2 \simeq 10^6$ in $γ^*(Q^2)p\toγ^*(Q^2) p$.

hep-ph↗
arXiv1997

η-η' -Glueball mixing from photon-meson transition form factors and decay ratio D_s --> ηl ν/ η' l ν

The background due to the direct diffractive dissociation of the photon into the $π^+π^-$-pair to the "elastic" diffractive $ρ^0$-meson production in electron-proton collisions is calculated. The amplitude for the background process $γp \to π^+ π^- p$ is proportional to the $π$-meson - proton cross section. Therefore, describing the HERA data, we can estimate $σ(πp)$ at energy $s_{πp}\sim (2 - 3) 10^{3} GeV^2$ that is considerably higher the existing data. At large $Q^2$ the interference between resonant and non-resonant $π^+ π^-$ production leads also to the more slow increase of the $σ^L/σ^T$ ratio with the mass of the $2π$ (i.e. $ρ^0$-meson) state.

hep-ph↗
arXiv1996

Photon--meson transition form factors $γπ^0$, $γη$ and $γη'$ at low and moderately high $Q^2$

We study photon--meson transition form factors $γ^*(Q^2)γ\to π^0,η,η'$ at low and moderately high virtualities $Q^2$ of one of the photons, the second photon being real. For the description of the form factor at low $Q^2$, a nontrivial quark--antiquark $(q\bar q)$ structure of the photon in the soft region is assumed, i.e. the photon is treated much like an ordinary vector meson. At large $Q^2$, along with a perturbative tail of the soft wave function, as it is for a hadron, the photon wave function contains also a standard QED point-like $q\bar q$ component. The latter provides the $1/Q^2$ behavior of the transition form factor at large $Q^2$ in accordance with perturbative QCD. Using the experimental results on $γπ^0$ form factor, we reconstruct the soft photon wave function which is found to have the structure similar to pion's, which has been formerly determined from a study of the elastic pion form factor. Assuming the universality of the ground--state pseudoscalar meson wave functions we calculate the transition form factors $γη$, $γη'$ and partial widths $η\toγγ$, $η'\toγγ$, in a perfect agreement with data.

hep-ph↗