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Register a new userNext-to-next-to-leading order ${cal O}(alpha^2alpha_s^2)$ results for top quark pair production in photon--photon collisions: The one-loop squared contributions
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We calculate the one-loop squared contributions to the next-to-next-to-leading order ${cal O}(alpha^2alpha_s^2)$ 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.
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We calculate the next-to-next-to-leading order ${cal O}(alpha_s^4)$ 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 ${cal O}(alpha_s^4)$ 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.
We calculate the next-to-next-to-leading order ${cal O}(alpha_s^4)$ 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 ${cal O}(alpha_s^4)$ 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.
We present the first calculation of the next-to-next-to-leading order threshold soft function for top quark pair production at hadron colliders, with full velocity dependence of the massive top quarks. Our results are fully analytic, and can be entirely written in terms of generalized polylogarithms. The scale-dependence of our result coincides with the well-known two-loop anomalous dimension matrix including the three-parton correlations, which at the two-loop order only appear when more than one massive partons are involved in the scattering process. In the boosted limit, our result exhibits the expected factorization property of mass logarithms, which leads to a consistent extraction of the soft fragmentation function. The next-to-next-to-leading order soft function obtained in this paper is an important ingredient for threshold resummation at the next-to-next-to-next-to-leading logarithmic accuracy.
We present predictions for the total ttbar production cross section sigma_ttbar at the Tevatron and LHC, which include the resummation of soft logarithms and Coulomb singularities through next-to-next-to-leading logarithmic order, and ttbar bound-state contributions. Resummation effects amount to about 8 % of the next-to-leading order result at Tevatron and about 3 % at LHC with 7 TeV centre-of-mass energy. They lead to a significant reduction of the theoretical uncertainty. With m_t=173.3 GeV, we find sigma_ttbar=7.22^{+0.31+0.71}_{-0.47-0.55} pb at Tevatron and sigma_ttbar=162.6^{+7.4+15.4}_{-7.5-14.7} at the LHC, in good agreement with the latest experimental measurements.
We study inclusive charged-hadron production in collisions of quasireal photons at NLO in perturbative QCD, using fragmentation functions recently extracted from PEP and LEP1 data. We superimpose the direct (DD), single-resolved (DR), and double-resolved (RR) gamma-gamma channels. First, we confront existing data taken by TASSO at PETRA and by MARK II at PEP with our NLO calculations. We also make comparisons with the neutral-kaon to charged-hadron ratio measured by MARK II. Then, we present NLO predictions for LEP2, a next-generation e+e- linear collider (NLC) in the TESLA design, and a Compton collider obtained by converting a NLC. We analyze transverse-momentum and rapidity spectra with regard to the scale dependence, the interplay of the DD, DR, and RR components, the sensitivity to the gluon density in the resolved photon, and the influence of gluon fragmentation. It turns out that the inclusive measurement of small-p_T hadrons at a Compton collider would greatly constrain the gluon density of the photon and the gluon fragmentation function.
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