NLO QCD corrections to five-jet production at LEP and the extraction of α s (M Z )

Abstract

Abstract:The highest exclusive jet multiplicity studied at LEP experiments is five. In this paper we compute the next-to-leading order QCD corrections to e + e − annihilation to five jets, essentially closing the (pure) perturbative QCD studies of exclusive jetty final states at LEP. We compare fixed-order perturbative results with ALEPH data. We estimate hadronization corrections to five-jet observables using the event generator SHERPA, which employs the CKKW procedure to combine a reliable perturbative treatment of highmultiplicity jet final states with parton showers. We show that a competitive value of the strong coupling constant α s (M Z ) = 0.1156 +0.0041 −0.0034 can be extracted from the distribution of the five-jet resolution parameter and the five-jet rate at LEP1 and LEP2.

One-loop calculations in quantum field theory: From Feynman diagrams to unitarity cuts

“…[123,124] it is possible to interface the one-loop calculation with a tool that provides the real emission corrections, the subtraction terms, and can carry out the phase space integration. Such an approach has been used recently to compute the NLO QCD corrections to five jet production in e + e − annihilation where one-loop amplitudes, calculated with generalized unitarity, were interfaced with Madevent/MadFKS [10].…”

“…In order to keep this discussion in line with the main theme of this review, we will assume that the OPP method is employed for the reduction of tensor integrals to the scalar basis, but a Passarino-Veltman reduction could also be used. We note that various implementations of diagrammatic calculations [125,126,10,124] can differ in the details -for example, in how the diagrams are grouped together before the numerical evaluation or in how the rational parts are computed, but are otherwise very similar in spirit.…”

“…In the past three years, a large number of one-loop computations with four (massive and massless) particles in the final state were completed [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] and even the first 2 → 5 resultsthe NLO QCD corrections to pp → W (Z) + 4j [17,18] -was obtained. 1 Some of this progress is to be attributed to spectacular improvements of the existing Feynman-diagrammatic algorithms for one-loop calculations, whose efficiency and stability was boosted beyond expectations.…”

“…(7.17), we need to explicitly construct Dirac matrices in higher dimensions. 10 To this end, we consider even space-time dimensionalities and follow the recursive definition given in Ref. [101].…”

Radiative Corrections in the LHC and ILC Era

“…Examples: pp, pp → W + 3, 4 jets [5,6,7,8], pp, pp → ttbb [9,10], pp → 4b [11], e + e − → 5 jets [12] at NLO QCD; pp, pp → H (with decays) [13,14], Drell-Yan (DY) production of single W or Z bosons (with decays) [15,16], e + e − → 3 jets [17,18] at NNLO QCD; e + e − → 4f [19,20] at NLO EW, • multi-scales: Logarithmic enhanced corrections of the form α k ln n (Q 2 1 /Q 2 2 ), Q 2 1 ≫ Q 2 2 are resummed up to NNLL accuracy. Examples: q T distributions in pp, pp → H [21] and in DY [22]; threshold corrections in top-pair production (for a review see, e. g., [23]); EW Sudakov logarithms in 4-fermion processes (for a review see, e. g., Ref.…”