International Europhysics Conference on HEP PROCEEDINGS Progress in QCD next-to-leading order calculations (original) (raw)
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Subtraction method of computing QCD jet cross sections at NNLO accuracy
Nuclear Physics B - Proceedings Supplements, 2008
We present a general subtraction method for computing radiative corrections to QCD jet cross sections at next-to-next-to-leading order accuracy. The steps needed to set up this subtraction scheme are the same as those used in next-to-leading order computations. However, all steps need non-trivial modifications, which we implement such that that those can be defined at any order in perturbation theory. We give a status report of the implementation of the method to computing jet cross sections in electron-positron annihilation at the next-to-next-to-leading order accuracy.
2008
In previous articles we outlined a subtraction scheme for regularizing doubly-real emission and real-virtual emission in next-to-next-to-leading order (NNLO) calculations of jet cross sections in electron-positron annihilation. In order to find the NNLO correction these subtraction terms have to be integrated over the factorized unresolved phase space and combined with the two-loop corrections. In this paper we perform the integration of all one-parton unresolved subtraction terms.
Journal of High Energy Physics, 2011
We perform the integration of all iterated singly-unresolved subtraction terms, as defined in ref. , over the two-particle factorized phase space. We also sum over the unresolved parton flavours. The final result can be written as a convolution (in colour space) of the Born cross section and an insertion operator. We spell out the insertion operator in terms of 24 basic integrals that are defined explicitly. We compute the coefficients of the Laurent expansion of these integrals in two different ways, with the method of Mellin-Barnes representations and sector decomposition. Finally, we present the Laurent expansion of the full insertion operator for the specific examples of electron-positron annihilation into two and three jets.
Physical Review D, 1994
Jet cross sections in deeply inelastic scattering in the case of transverse photon exchange for the production of (1+1) and (2+1) jets are calculated in next-to-leading order QCD (here the `+1' stands for the target remnant jet, which is included in the jet definition for reasons that will become clear in the main text). The jet definition scheme is based on a modified JADE cluster algorithm. The calculation of the (2+1) jet cross section is described in detail. Results for the virtual corrections as well as for the real initial- and final state corrections are given explicitly. Numerical results are stated for jet cross sections as well as for the ratio sigmamboxsmall(2+1)jet/sigmamboxsmalltot\sigma_{\mbox{\small (2+1) jet}}/\sigma_{\mbox{\small tot}}sigmamboxsmall(2+1)jet/sigmamboxsmalltot that can be expected at E665 and HERA. Furthermore the scale ambiguity of the calculated jet cross sections is studied and different parton density parametrizations are compared.
NNLO QCD corrections to diphoton production with an additional jet at the LHC
Journal of High Energy Physics, 2021
We calculate the NNLO QCD corrections to diphoton production with an additional jet at the LHC. Our calculation represents the first NNLO-accurate prediction for the transverse momentum distribution of the diphoton system. The improvement in the accuracy of the theoretical prediction is significant, by a factor of up to four relative to NLO QCD as estimated through scale variations. Our calculation is exact except for the finite remainder of the two-loop amplitude which is included at leading color. The numerical impact of this approximated contribution is small. The results of this work are expected to further our understanding of the Higgs boson sector and of the behavior of higher-order corrections to LHC processes.
Hadronic top-quark pair production in association with two jets at next-to-leading order QCD
Physical Review D, 2011
We report on the calculation of the next-to-leading order QCD corrections to the production of tt pairs in association with two hard jets at the Fermilab TeVatron and CERN Large Hadron Collider. Results for the integrated and differential cross sections are given. The corrections with respect to leading order are negative and moderate. A study of the scale dependence of our NLO predictions indicates that the residual theoretical uncertainty, due to higher order corrections, is 21% for the TeVatron and 15% for the LHC. In case of the TeVatron, the forward-backward asymmetry of the top quark is calculated for the first time at next-to-leading order. With the inclusive selection of cuts, this asymmetry amounts to A t FB,LO = −10.3% at leading order and A t FB,NLO = −4.6% at next-to-leading order. All results presented in this paper have been obtained with the help of the Helac-Nlo package.
Journal of High Energy Physics, 2014
The moments of the single inclusive momentum distribution of hadrons in QCD jets, are studied in the next-to-modified-leading-log approximation (NMLLA) including next-to-leading-order (NLO) corrections to the α s strong coupling. The evolution equations are solved using a distorted Gaussian parametrisation, which successfully reproduces the spectrum of charged hadrons of jets measured in e + e − collisions. The energy dependencies of the maximum peak, multiplicity, width, kurtosis and skewness of the jet hadron distribution are computed analytically. Comparisons of all the existing jet data measured in e + e − collisions in the range √ s ≈ 2-200 GeV to the NMLLA+NLO * predictions allow one to extract a value of the QCD parameter Λ QCD , and associated two-loop coupling constant at the Z resonance α s (m 2 Z) = 0.1195 ± 0.0022, in excellent numerical agreement with the current world average obtained using other methods.
Higher-order corrections to QCD jets
Physics Letters B, 1988
Motivated by recent calculations of matrix elements for O (a3) parton-parton scattering processes, we evaluate the K-factors and the relative transverse-momentum distributions for jet production at high PT. We present results for a set of parton-parton subprocesses involving quarks of different flavours, in the framework of a general analysis of all one-loop QCD corrections.