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Z. Merebashvili

Publications and source records attributed to Z. Merebashvili.

16 recordsLinked to original sources
arXiv2008

Heavy quark pair production in gluon fusion at next-to-next-to-leading ${\cal O}(α_s^4)$ order: One-loop squared contributions

We calculate the next-to-next-to-leading order ${\cal O}(α_s^4)$ one-loop squared corrections to the production of heavy-quark pairs in the gluon-gluon fusion process. Together with the previously derived results on the $q \bar{q}$ production channel the results of this paper complete the calculation of the one-loop squared contributions of the next-to-next-to-leading order ${\cal O}(α_s^4)$ radiative QCD corrections to the hadroproduction of heavy flavors. Our results, with the full mass dependence retained, are presented in a closed and very compact form, in dimensional regularization.

hep-ph↗
arXiv2008

Next-to-next-to-leading order ${\cal O}(α_s^4)$ results for heavy quark pair production in quark--antiquark collisions: The one-loop squared contributions

We calculate the next-to-next-to-leading order ${\cal O}(α_s^4)$ one-loop squared corrections to the production of heavy quark pairs in quark-antiquark annihilations. These are part of the next-to-next-to-leading order ${\cal O}(α_s^4)$ radiative QCD corrections to this process. Our results, with the full mass dependence retained, are presented in a closed and very compact form, in the dimensional regularization scheme. We have found very intriguing factorization properties for the finite part of the amplitudes.

hep-ph↗
arXiv2006

Next-to-next-to-leading order ${\cal O}(α^2α_s^2)$ results for top quark pair production in photon--photon collisions: The one-loop squared contributions

We calculate the one-loop squared contributions to the next-to-next-to-leading order ${\cal O}(α^2α_s^2)$ radiative QCD corrections for the production of heavy quark pairs in the collisions of unpolarized on--shell photons. In particular, we present analytical results for the squared matrix elements that correspond to the product of the one--loop amplitudes. All results of the perturbative calculation are given in the dimensional regularization scheme. These results represent the Abelian part of the corresponding gluon--induced next-to-next-to-leading order cross section for heavy quark pair hadroproduction.

hep-ph↗
arXiv2006

Laurent series expansion of a class of massive scalar one-loop integrals up to ${\cal O}(\ep^2)$ in terms of multiple polylogarithms

In a recent paper we have presented results for a set of massive scalar one-loop master integrals needed in the NNLO parton model description of the hadroproduction of heavy flavors. The one--loop integrals were evaluated in $n=4-2\ep$ dimension and the results were presented in terms of a Laurent series expansion up to ${\cal O}(\ep^2)$. We found that some of the $\ep^2$ coefficients contain a new class of functions which we termed the $L$ functions. The $L$ functions are defined in terms of one--dimensional integrals involving products of logarithm and dilogarithm functions. In this paper we derive a complete set of algebraic relations that allow one to convert the $L$ functions of our previous approach to a sum of classical and multiple polylogarithms. Using these results we are now able to present the $\ep^2$ coefficients of the one-loop master integrals in terms of classical and multiple polylogarithms.

hep-ph↗
arXiv2006

One-loop amplitudes for four-point functions with two external massive quarks and two external massless partons up to O(epsilon^2)

We present complete analytical ${\mathcal O}(ε^2)$ results on the one-loop amplitudes relevant for the NNLO quark-parton model description of the hadroproduction of heavy quarks as given by the so-called loop-by-loop contributions. All results of the perturbative calculation are given in the dimensional regularization scheme. These one-loop amplitudes can also be used as input in the determination of the corresponding NNLO cross sections for heavy flavor photoproduction, and in photon-photon reactions.

hep-ph↗
arXiv2005

Laurent series expansion of a class of massive scalar one-loop integrals to ${\cal O}(\ep^2)

We use dimensional regularization to calculate the ${\cal O}(\ep^2)$ expansion of all scalar one-loop one-, two-, three- and four-point integrals that are needed in the calculation of hadronic heavy quark production. The Laurent series up to ${\cal O}(\ep^2)$ is needed as input to that part of the NNLO corrections to heavy flavor production at hadron colliders where the one-loop integrals appear in the loop-by-loop contributions. The four-point integrals are the most complicated. The ${\cal O}(\ep^2)$ expansion of the three- and four-point integrals contains in general polylogarithms up to ${\rm Li}_4$ and functions related to multiple polylogarithms of maximal weight and depth four.

hep-ph↗
arXiv2002

One-loop corrections to four-point functions with two external massive fermions and two external massless partons

We present a complete set of one-loop matrix elements relevant for the hadroproduction of heavy quarks in next-to-leading order employing dimensional regularization to isolate ultraviolet and soft divergences. All results of the perturbative calculation are given in detail. These one-loop matrix elements can also be used as input in the determination of the corresponding next-to-leading order cross sections for heavy flavor photoproduction and in photon-photon reactions, as well as for any of the relevant crossed processes. Our results are tested against the results of other related studies in which unpolarized and longitudinally polarized processes were considered.

hep-ph↗
arXiv2002

Approximate Next-to-Leading Order and Next-to-Next-to-Leading Order Corrections

For processes involving structure functions and/or fragmentation functions, arguments that, over a range of a proper kinematic variable, there is a part that dominates the next-to-leading order (NLO) corrections are briefly reviewed. The arguments are tested against more recent NLO and in particular complete next-to-next-to-leading order (NNLO) calculations. A critical examination of when these arguments may not be useful is also presented.

hep-ph↗
arXiv2000

Analyticity, crossing and the absorptive parts of the one-loop contributions to the quark-quark-gluon gauge boson four-point function

Starting from the known one-loop result for the $e^{+}e^{-}$-annihilation process $e^{+}e^{-}\stackrel{γ,Z} {\longrightarrow} q\bar{q}g$ with massless quarks we employ analyticity and crossing to determine the absorptive parts of the corresponding one-loop contributions in Deep Inelastic Scattering (DIS) and in the Drell-Yan process (DY). Whereas the ${\cal O}(α_s^2)$ absorptive parts generate a non-measurable phase factor in the $e^{+}e^{-}$-annihilation channel one obtains measurable phase effects from the one-loop contributions in the deep inelastic and in the Drell-Yan case. We compare our results with the results of previous calculations where the absorptive parts in DIS and in the DY process were calculated directly in the respective channels. We also present some new results on the dispersive and absorptive contributions of the triangle anomaly graph to the DIS process.

hep-ph↗
arXiv2000

Next-to-Leading Order Corrections to Heavy Flavour Production in Longitudinally Polarized Photon-Nucleon Collisions

A complete next-to-leading order calculation of longitudinally polarized heavy quark photoproduction is presented. All results of the purturbative calculation are given in detail. For reactions and energies of interest cross sections differential in the transverse momentum and rapidity of the heavy quark, total cross sections and the corresponding asymmetries are given. Errors in the asymmetries are estimated and the possibility to distinguish between various scerarios of the polarized gluon distribution is discussed. Our results are compared with other related publications.

hep-ph↗
arXiv2000

Polarized Photoproduction of Heavy Quarks in Next-to-Leading Order

The results of a next-to-leading order calculation of heavy quark production in longitudinally polarized photon-nucleon collisions are presented. At c.m. energy $\sqrt{S}=10$ GeV, for $\vec γ+\vec p \to c+X$, cross sections differential in the transverse momentum and rapidity of the charmed quark $c$ and the corresponding asymmetries are presented; also, as functions of $\sqrt{S}$, integrated cross sections, $K$-factors and the corresponding asymmetries are given. Errors in the asymmetries are estimated and the possibility to distinguish between three scerarios differing essentially in the polarized gluon distribution is discussed.

hep-ph↗
arXiv1998

Analytically integrated results for heavy fermion production in two-photon collisions and a high precision $α_s$ determination

The cross section for massive fermion production in two-photon collisions was examined at next-to-leading order in QCD/QED for general photon helicity. The delta function (virtual+soft) part of the differential cross section was analytically integrated over the final state phase space. Series expansions for the complete differential and total cross sections were given up to tenth order in the parameter $β$. These were shown to be of practical use and revealed much structure. Accurate parametrizations of the total cross sections were given, valid up to higher energies. The above results were applied to top quark production in the region not too far above threshold. The cross section was shown to be quite sensitive to $α_s$ in the appropriate energy region.

hep-ph↗
arXiv1998

Analytically expanded and integrated results for massive fermion production in two-photon collisions and a high precision alpha_s determination

The cross section for massive fermion production in two-photon collisions was examined at next-to-leading order in QCD/QED for general photon helicity. The delta function (virtual+soft) part of the differential cross section was analytically integrated over the final state phase space. Series expansions for the complete differential and total cross sections were given up to tenth order in the parameter beta. These were shown to be of practical use and revealed much structure. Accurate parametrizations of the total cross sections were given, valid up to higher energies. The above results were applied to top quark production in the region not too far above threshold. The cross section was shown to be quite sensitive to alpha_s in the appropriate energy region.

hep-ph↗
arXiv1996

Direct photon production in polarized hadron collisions at collider and fixed target energies

Recently determined next-to-leading order sets of polarized parton distributions are used to study large-p_T $\vec{p}\vec{p}\rightarrow γ+X$ at $\sqrt{s}=38, 100 and 500 GeV$. Certain conversion terms, necessary to use the above sets, are determined. It is concluded that, to distinguish between the above sets, planned RHIC experiments should be successful, in particular at c.m. photon pseudorapidity $\simeq 1$, and that a proposed HERA-$\vec{N}$ fixed target experiment should have rather large accuracy at relatively large $x_T (=2p_T/\sqrt{s})$.

hep-ph↗
arXiv1996

Heavy-Quark Production by Polarized and Unpolarized Photons in Next-to-Leading Order

Complete analytical results for the production of heavy-quark pairs by polarized and unpolarized photons in next-to-leading order are presented. Two-, three- and two plus three-jet cross sections for total photon spin $J_z=0,\pm 2$ are presented for $b\bar{b}(g)$ production. The 2-jet cross sections are considered as a background to $γγ\rightarrow H^* \rightarrow b\bar{b}$ (standard model). Top production, not too far above threshold, is also considered for $J_z=0,\pm 2$. For both $b$- and $t$-quark production, the higher order QCD corrections are found to be significant.

hep-ph↗