arXiv subjects
Publications and source records attributed to Yu. M. Shabelski.
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. At large $Q^2$ the interference between resonant and non-resonant $π^+ π^-$ production changes the $σ^L/σ^T$ ratio with the mass of the $2π$ (i.e. $ρ^0$-meson) state.
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 $s_{πp}\sim (2 - 3) \times 10^{3}$ 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.
We discuss the experimental indications on the behaviour of F_2(x,Q^2) at small x both in proton and nuclear targets. By comparing the parametrizations of the data we conclude that shadowing correction effects in a proton target can appear at a noticeable level for x=(2 - 4)\times10^{-4} and Q^2\sim 10^1 GeV^2, namely inside the HERA regime.
We calculate the A-dependence of open charm and beauty as well as Drell-Yan pair production cross sections on nuclear targets taking into account the difference of quark and gluon distributions in free and bound nucleons. The results are presented for both proton-nucleus and nucleus-nucleus collisions. For the case of heavy flavour production at comparatively low energies, if $σ\sim A^α$, the values of $α$ are slightly higher than unity. With increasing energy $α$ decreases in all cases and becomes smaller than unity. We also show $α$ as a function of Feynman-$x$ of the produced $Q\overline{Q}$ or $l^+l^-$ pair and obtain that it decreases significantly in the beam fragmentation region. The sensitivity of our results to the used set of parton distributions is also discussed.
It is shown that the fusion of strings is a source of particle production in nucleus--nucleus collisions outside the kinematical limits of nucleon--nucleon collisions. The spectrum of different particles is compared with the high energy data on p--A collisions obtaining a reasonable agreement. Results for A--B collisions at $\sqrt{s}=19.4$ AGeV and $\sqrt{s}=200$ AGeV are given. It is shown that the fusion of strings can accelerate particles up to the highest energy detected in cosmic rays without help of any additional cosmic accelerator. Also the rise of the average shower depth of maximun for cosmic rays in the energy range between $10^{16}$ eV and $10^{19}$ eV can be explained by the same mechanism without requiring any change in the chemical composition.
A resently developed generalization of the Quark--Gluon String Model to the case of bosonic resonances production in hadron--hadron collisions is used for the calculation of inclusive production of charmed mesons $D$, $D^*(2010)$ and $D^{*}_{2}(2460)$. A simple relation which determines the dependence of the charmed meson production cross sections on their spin J is obtained. It is shown that the theoretical predictions for the inclusive spectra and production cross sections of these charmed mesons are confirmed experimentally with a reasonable accuracy.
It is shown that the fusion of strings is a source of particle production in nucleus--nucleus collisions outside the kinematical limits of nucleon--nucleon collisions. This fact, together with another effect of string fusion, the reduction of multiplicities, sheds some light on two of the main problems of ultrahigh energy cosmic rays, the chemical composition and the energy of the most energetic detected cosmic rays.
The inclusion of string fusion in Dual Parton Model results in the appearance of diquark-antidiquark pairs in the sea with comparatively large Feynman-$x$. Such antidiquarks can fragment into fast antibaryons, thus increasing several times the corresponding yields in high energy $pp$ collisions for $x_F \sim 0.8 ÷0.9$. String fusion also results in an unusual dependence of inclusive spectra on the multiplicity of secondaries. Some numerical estimations are presented.
We consider the light quark electroproduction cross section and show that the contribution coming from the infrared ($q_T<300\, MeV$) region is not negligible. It changes the $F_2(x,Q^2)/xG(x,Q^2)$ ratio by 20-30\% (or even more) for small $x$ and $Q^2\sim 4\, GeV^2$.
We calculate the A-dependence of charm and beauty production cross sections on nuclear targets taking into account the difference of quark and gluon distributions in free nucleons and in nucleus. At comparatively low energies, if $σ\sim A^α$, the value of $α$ is slightly higher than unity. With the growth of the initial energy the value of $α$ decreases and becomes smaller than unity. We also calculate the values of $α$ for different Feynman-$x$ of the produced $Q\overline{Q}$ pair and obtain that they decrease significantly in the beam fragmentation region.
The cross sections of heavy quark production in $pp$ collision and for their photo- and electroproduction are calculated in the framework of QCD. The virtual nature of the interacting gluons as well as their transverse motion and different polarizations are taken into account. The obtained cross sections exhibit more rapid growth with the initial energy than the parton model predictions and the $p_T$ distributions of produced heavy quarks are more smooth.
Production of charmed and beauty mesons and baryons in hadron-nucleon collisions at not very high energy is considered in the framework of the Quark-Gluon String Model. We take into account the possible corrections to the model which disappear at asymptotically high energies but could be important at comparatively low energies, essentially in the case of heavy flavour production. The case of nuclear targets is also considered and the $A$-dependence of charmed and beauty hadron yields is calculated. Predictions for the case of beauty hadron production at $\sqrt{s}$ = 39 GeV are presented.