Sebastian Klein

Hadronic top-quark pair production with NNLL threshold resummation

Abstract We compute the total top-quark pair production cross section at the Tevatron and LHC based on approximate NNLO results, and on the summation of threshold logarithms and Coulomb enhancements to all orders with next-to-next-to-leading logarithmic (NNLL) accuracy, including bound-state effects. We find σ t t ¯ ( Tevatron ) = ( 7.22 − 0.47 + 0.31 − 0.55 + 0.71 ) pb , σ t t ¯ ( LHC , s = 7 TeV ) = ( 162.6 − 7.6 + 7.4 − 14.7 + 15.4 ) pb for m t = 173.3 GeV . The implementation of joint soft and Coulomb resummation, its ambiguities, and the present theoretical uncertainty are discussed in detail. We further obtain new approximate results at N3LO.

Mellin moments of the O(αs3) heavy flavor contributions to unpolarized deep-inelastic scattering at Q2≫m2 and anomalous dimensions

Abstract We calculate the O ( α s 3 ) heavy flavor contributions to the Wilson coefficients of the structure function F 2 ( x , Q 2 ) and the massive operator matrix elements (OMEs) for the twist-2 operators of unpolarized deeply inelastic scattering in the region Q 2 ≫ m 2 . The massive Wilson coefficients are obtained as convolutions of massive OMEs and the known light flavor Wilson coefficients. We also compute the massive OMEs which are needed to evaluate heavy flavor parton distributions in the variable flavor number scheme (VFNS) to 3-loop order. All contributions to the Wilson coefficients and operator matrix elements but the genuine constant terms at O ( α s 3 ) of the OMEs are derived in terms of quantities, which are known for general values in the Mellin variable N. For the operator matrix elements A Q g ( 3 ) , A q g , Q ( 3 ) and A g g , Q ( 3 ) the moments N = 2 – 10 , for A Q q ( 3 ) , PS to N = 12 , and for A q q , Q ( 3 ) , NS , A q q , Q ( 3 ) , PS , A g q , Q ( 3 ) to N = 14 are computed. These terms contribute to the light flavor +-combinations. For the flavor non-singlet terms, we calculate as well the odd moments N = 1 – 13 , corresponding to the light flavor −-combinations. We also obtain the moments of the 3-loop anomalous dimensions, their color projections for the present processes respectively, in an independent calculation, which agree with the results given in the literature.

Two-Loop Massive Operator Matrix Elements and Unpolarized Heavy Flavor Production at Asymptotic Values Q 2 ≫ m 2 ∗

Abstract We calculate the O ( α s 2 ) massive operator matrix elements for the twist-2 operators, which contribute to the heavy flavor Wilson coefficients in unpolarized deeply inelastic scattering in the region Q 2 ≫ m 2 . The calculation has been performed using light-cone expansion techniques. We confirm an earlier result obtained in [M. Buza, Y. Matiounine, J. Smith, R. Migneron, W.L. van Neerven, Nucl. Phys. B 472 (1996) 611, hep-ph/9601302 ]. The calculation is carried out without using the integration-by-parts method and in Mellin space using harmonic sums, which lead to a significant compactification of the analytic results derived previously. The results allow to determine the heavy flavor Wilson coefficients for F 2 ( x , Q 2 ) to O ( α s 2 ) and for F L ( x , Q 2 ) to O ( α s 3 ) for all but the power suppressed terms ∝ ( m 2 / Q 2 ) k , k ⩾ 1 .

The O(\alpha_s^3) Massive Operator Matrix Elements of O(n_f) for the Structure Function F_2(x,Q^2) and Transversity

The contributions ∝nf to the O(αs3) massive operator matrix elements describing the heavy flavor Wilson coefficients in the limit Q2≫m2 are computed for the structure function F2(x,Q2) and transversity for general values of the Mellin variable N. Here, for two matrix elements, Aqq,QPS(N) and Aqg,Q(N), the complete result is obtained. A first independent computation of the contributions to the 3-loop anomalous dimensions γqg(N), γqqPS(N), and γqqNS,(TR)(N) is given. In the computation advanced summation technologies for nested sums over products of hypergeometric terms with harmonic sums have been used. For intermediary results generalized harmonic sums occur, while the final results can be expressed by nested harmonic sums only.

Massive 3-loop Ladder Diagrams for Quarkonic Local Operator Matrix Elements

Abstract 3-loop diagrams of the ladder-type, which emerge for local quarkonic twist-2 operator matrix elements, are computed directly for general values of the Mellin variable N using Appell-function representations and applying modern summation technologies provided by the package Sigma and the method of hyperlogarithms. In some of the diagrams generalized harmonic sums with ξ ∈ { 1 , 1 / 2 , 2 } emerge beyond the usual nested harmonic sums. As the asymptotic representation of the corresponding integrals shows, the generalized sums conspire giving well behaved expressions for large values of N . These diagrams contribute to the 3-loop heavy flavor Wilson coefficients of the structure functions in deep-inelastic scattering in the region Q 2 ≫ m 2 .

Modern Summation Methods and the Computation of 2- and 3-loop Feynman Diagrams

By symbolic summation methods based on difference fields we present a general strategy that transforms definite multi-sums, e.g., in terms of hypergeometric terms and harmonic sums, to indefinite nested sums and products. We succeeded in this task with all our concrete calculations of 2--loop and 3--loop massive single scale Feynman diagrams with local operator insertion.

Inclusive top-pair production phenomenology with TOPIXS

A bstractWe discuss various aspects of inclusive top-quark pair production based on Topixs, a new, flexible program that computes the production cross section at the Tevatron and LHC at next-to-next-to-leading logarithmic accuracy in soft and Coulomb resummation, including bound-state effects and the complete next-to-next-to-leading order result in the

Longitudinal heavy quark structure function FLQQ¯ in the region Q2≫m2 at O(αs3)

q\overline q

The

channel, which has recently become available. We present the calculation of the top-pair cross section in pp collisions at 8 TeV centre-of-mass energy, as well as the cross sections for hypothetical heavy quarks in extensions of the standard model. The dependence on the parton distribution input is studied. Further we investigate the impact of LHC top cross section measurements at

O(\alpha_s^3 n_f T_F^2 C_{A,F})

\sqrt {s} = {7}