arXiv subjects
Publications and source records attributed to A. I. Ahmadov.
The process $e^+e^- \to π^0ρ$ is described in the framework of the expanded NJL model in the energy region from 0.9 GeV to 1.5 GeV. The contribution of intermediate state with vector mesons $ω(782), \,\,ϕ(1020)$, and $ω'(1420)$, where $ω'$ is the first radial excitation of $ω$ - meson was taken into account. Results obtained are in satisfactory agreement with experimental data.
The high energy amplitudes of the large angles Moller scattering are calculated in frame of chiral basis in Born and 1-loop QED level. Taking into account as well the contribution from emission of soft real photons the compact relations free from infrared divergences are obtained. The expressions for separate chiral amplitudes contribution to the cross section are in agreement with renormalization group predictions.
In this article, we investigate the next-to-leading order contribution of the higher-twist Feynman diagrams to the large-$p_T$ inclusive pion production cross section in proton-proton collisions and present the general formulae for the higher-twist differential cross sections in the case of the running coupling and frozen coupling approaches. We compared the resummed next-to-leading order higher-twist cross sections with the ones obtained in the framework of the frozen coupling approach and leading-twist cross section. The structure of infrared renormalon singularities of the higher twist subprocess cross section and it's resummed expression (the Borel sum) are found. It is shown that the resummed result depends on the choice of the meson wave functions used in the calculations. We discuss the phenomenological consequences of possible higher-twist contributions to the meson production in proton-proton collisions in next-to-leading order at RHIC.
Differential distributions in the $π_0π_0γ$ system created in the annihilation channel of an electron-positron collision are considered. The energy fractions of the pions (Dalitz-plot) distribution are presented in a general form and in approximation of intermediate vector mesons (excited and ordinary ones).It is pointed out that in relevant experiments the generalized polarizability of the neutral pion can be measured. Numerical illustrations are presented.
Differential cross section of processes with high energy $p(\bar p)p$ collisions in frames of QED: creation of scalar, pseudoscalar and lepton pair - are considered in Weizsäcker - Williams approximation. In frames of QCD processes with conversion of initial proton (antiproton) to fermionic jets accompanied with one gluon jet as well as the state of two gluons and quark-antiquark pair (with out rapidity gap) are considered in frames of effective Reggion action of theory of Lipatov. Process of creation of a Higgs boson accompanied with two fermionic jets is considered. The azimuthal correlation in process of two gluon jet separated by rapidity gap is investigated. Effects of gluon reggeization are taken into account. Some distributions are illustrated by numerical calculations.
The annihilation of proton and antiproton to electron-positron pair, including radiative corrections due to the emission of virtual and real photons is considered. The results are generalized to leading and next-to leading approximations. The relevant distributions are derived and numerical applications are given in the kinematical range accessible to the PANDA experiment at the FAIR facility.
In this article, we investigate the contribution of the higher-twist Feynman diagrams to the large-$p_T$ inclusive single meson production cross section in photon-photon collisions and present the general formulas for the higher-twist differential cross sections in case of the running coupling and frozen coupling approaches. The structure of infrared renormalon singularities of the higher-twist subprocess cross section and the resummed expression (the Borel sum) for it are found. We compared the resummed higher-twist cross sections with the ones obtained in the framework of the frozen coupling approach and leading-twist cross section. We obtain, that ratio $R=(Σ_{M^{+}}^{HT})^{res}$ / $(Σ_{M^{+}}^{HT})^{0}$, for all values of the transverse momentum $p_{T}$ of the meson identically equivalent to ratio $r$=($Δ_{M}^{HT})^{res}$ / $(Δ_{M}^{HT})^{0}$. It is shown that the resummed result depends on the choice of the meson wave functions used in calculation. Phenomenological effects of the obtained results are discussed.
We calculate the contribution of semi-hadronic states with pseudoscalar $P=π^0, η$ and scalar ($σ$(550))meson accompanied with real photon as an intermediate state of a heavy photon to the anomalous magnetic moment of muon. We consider the intermediate states with $π_0$ and $σ$ as a hadrons in frames of Nambu-Jona-Lasinio model. The contribution of $π_0γ$ state is in agreement with results obtained in previous theoretical considerations as well as with experimental data $a_μ^{π_0γ}\approx 4.5 \times 10^{-10}$, besides we estimate $a_μ^{ηγ}=0.7 \times 10^{-10}, a_μ^{σγ} \sim 1.5 \times 10^{-11}, a_μ^{π^+π^-γ} \sim 3.2 \times 10^{-10}.$ We discass as well the LbL mechanism with $a_μ^{lbl}=10.5 \cdot 10^{-10}.$
Charge-odd correlation of the charged pair components produced at electron-proton scattering can measure three current correlation averaged by proton state. In general these type correlation can be described by 14 structure functions. We restrict here by consideration of inclusive distributions of a pair components, which is the light-cone projection of the relevant hadronic tensor. Besides we consider the point-like approximation for proton and pion. Numerical estimations show that charge-odd effects can be measured in exclusive ep -> 2 pi X experiments.
Taking into account the exchange forces between protons of scalar, pseudoscalar, vector and axial vector type the cross sections of neutral and charged scalar mesons $a_0(980)$, $a_+(980)$, $f_0(980)$, $σ(600)$ production are calculated. The estimation for the facilities of moderately high energies such as PANDA and NICA are presented. Similar analysis is given for processes of charged and neutral Higgs boson production at high energy proton-proton colliders such as Tevatron, RHIC and LHC. The possible signal of neutral Higgs boson decay into two oppositely charged leptons of different kinds is discussed. Numerical estimations for parameters of modern colliders are given.
In this work, the analytical solution of the radial Schrödinger equation for the Woods-Saxon potential is presented. In our calculations, we have applied the Nikiforov-Uvarov method by using the Pekeris approximation to the centrifugal potential for arbitrary $l$ states. The bound state energy eigenvalues and corresponding eigenfunctions are obtained for various values of $n$ and $l$ quantum numbers.
The cross section for different processes induced by $e^+e^-$ annihilation, in the kinematical limit $β_μ\approxβ_π=(1-m_π^2/ε^2)^{1/2}\sim 1$, is calculated taking into account first order corrections to the amplitudes and the corrections due to soft emitted photons, with energy $ω\leΔE\le ε$ in the center of mass of the $e^+e^-$ colliding beams. The results are given separately for charge--odd and charge--even terms in the final channels $π^+π^-(γ)$ and $μ^+μ^-(γ)$. In case of pions, form factors are taken into account. The differential cross sections for the processes: $e^++e^-\to e^++e^-(+γ)$, $\to π^++π^-(γ)$, $\to μ^++μ^-(γ),\to γγ(γ)$ have been calculated and the corresponding formula are given in the ultrarelativistic limit $\sqrt{s}/2= ε\gg m_μ\sim m_π$ . For a quantitative evaluation of the contribution of higher order of the perturbation theory, the production of $π^+π^-$, including radiative corrections, is calculated in the approach of the lepton structure functions. This allows to estimate the precision of the obtained results as better than 0.5% outside the energy region corresponding to narrow resonances. A method to integrate the cross section, avoiding the difficulties which arise from singularities is also described.
Cross section of the processes of neutral pion production as well as pairs of charged fermions and bosons in peripherical interaction of leptons, photons are calculated in main logarithmical approximation. We investigate the phase volumes and differential cross sections. The differential cross section of few neutral pions and a few pairs production are written down explicitly. Considering the academic problem of summation on the number of pairs for the case of massless particles we reproduce the known results obtained in seventies of last century. The possibility to construct the generator for Monte-Carlo modeling of this processes basing of this results are discussed.
In this article, we investigate the contribution of the high twist Feynman diagrams to the large $p_{T}$ single pseudoscalar and vector mesons inclusive production cross section in two-photon collisions and we present the general formulae for the high and leading twist differential cross sections. The pion wave function where two non-trivial Gegenbauer coefficients $a_2$ and $a_4$ have been extracted from the CLEO data, Braun-Filyanov pion wave function, the asymptotic and the Chernyak-Zhitnitsky wave functions are used in the calculations. For $ρ$-meson we used Ball-Braun wave function. The results of all the calculations reveal that the high twist cross sections, the ratio R, the dependence transverse momentum $p_{T}$ and the rapidity $y$ of meson in $Φ_{CLEO}(x,Q^2)$ wave function case is very close to the $Φ_{asy}(x)$ asymptotic wave function case. It is shown that the high twist contribution to the cross section depends on the choice of the meson wave functions.
In this article, we investigate the Drell-Yan process of the light neutralino pair $\widetildeχ_{i}^{0}\widetildeχ_{j}^{0}$ ($i,j=1,2$) productions at proton-proton collisions and we present the general formulate for the differential cross sections. We conduct an extensive examination of the dependence of the total cross section of the subprocesses $q \bar q \to \widetilde χ_{i}^{0}\widetildeχ_{j}^{0}$ on the beam energy, on the mass of the squarks and also on the $M_2$ gaugino for the three extremely different scenarios. For all three cases, the outcomes are as follows. The dependence of the total cross section of the subprocesses $q \bar q \to \widetilde χ_{i}^{0} \widetilde χ_{j}^{0}$ on the beam energy is dominated by one of the subprocesses, $q \bar q \to \widetilde χ_{1}^{0} \widetilde χ_{2}^{0}$. On the other hand, the dependence of the total cross section of the subprocesses $q \bar q \to \widetilde χ_{i}^{0} \widetilde χ_{j}^{0}$ on the mass of the squarks is dominated by one of the subprocesses, $q \bar q \to \widetilde χ_{1}^{0} \widetilde χ_{2}^{0}$. We derive there from that our findings may lead to new insights relating to experimental investigations and these dependencies may be used as bases of an experimental research for the neutralino pair at LHC.
We consider the charge-odd correlations (COC) in cross sections of processes of production of charged particles. The cases of a muonic pair and pion systems $π^{+}π^{-},π^{+}π^{-}π^{0}$ are considered in detail for electron-proton or photon-proton collisions in the proton fragmentation region kinematics. COC arise from interference of amplitudes which describe the different mechanisms of charged leptons (pions) creation. One of them corresponds to production of particles in the charge-odd state (one virtual photon or vector meson annihilation to this system of particles) and the other corresponds to the charge-even state of produced particles (creation by two photons). COC for muon-antimuon pair creation have a pure QED nature and can be considered as a normalization process. The processes with pion production are sensitive to some characteristics of proton wave functions and, besides, can be used for checking the anomalous and normal parts of the effective pionic lagrangian. Three electromagnetic currents operator matrix element can be measured in photon-proton interactions with lepton pair production. For this aim a charge-odd combination of cross sections can be constructed as a conversion of leptonic 3-rank tensor with hadronic ones. These experiments can be considered as an alternative to deep virtual Compton scattering.
In this article, we investigate the contribution of the high twist Feynman diagrams to the large-$p_T$ pion production cross section in proton-proton collisions and we present the general formulae for the high and leading twist differential cross sections. The pion wave function where two non-trivial Gegenbauer coefficients $a_2$ and $a_4$ have been extracted from the CLEO data, two other pion model wave functions, $P_2$, $P_3$, the asymptotic and the Chernyak-Zhitnitsky wave functions are used in the calculations. The results of all the calculations reveal that the high twist cross sections, the ratios $R$, $r$, the dependence transverse momentum $p_T$ and the rapidity $y$ of pion in the $Φ_{CLEO}(x,Q^2)$ wave function case is very close to the $Φ_{asy}(x)$ asymptotic wave function case. It is shown that the high twist contribution to the cross section depends on the choice of the meson wave functions.
In this work we investigate the single- and the double- spin asymmetries at the collisions of polarized protons $pp \to (γ*, Z^0,Z')+X within the scope of QCD, electroweak interaction and superstring E_6 theory. The helicity amplitude method is used. Analytical expressions for the single- and the double- spin asymmetries are obtained and their dependence from the transverse momentum of lepton pair is investigated at the three different values of invariant masses of lepton pair. Has been extracted pure contribution coming from superstring Z' boson on the single- and double- spin asymmetries. The obtained results allow to investigate the spin structure of the proton.