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Hadronic production of a Higgs boson in association with two jets at ...

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2.8. Recent progress: One-loop autom<strong>at</strong>is<strong>at</strong>ion 67Blackh<strong>at</strong> [126, 178–181] is a program which implements the four-dimensionalmethods described <strong>in</strong> this chapter. The Laurent expansion method [122] is applied<strong>in</strong> four dimensions to determ<strong>in</strong>e the coefficients <strong>of</strong> the cut-constructible pieces. Ther<strong>at</strong>ional pieces are then calcul<strong>at</strong>ed us<strong>in</strong>g the unitarity-bootstrap approach <strong>with</strong> multipleshifts [124,161–165]. The program also <strong>in</strong>cludes the D-dimensional applic<strong>at</strong>ion<strong>of</strong> the Laurent expansion [172] for an altern<strong>at</strong>e method <strong>of</strong> gener<strong>at</strong><strong>in</strong>g the r<strong>at</strong>ionalterms. This program has been successfully <strong>in</strong>tegr<strong>at</strong>ed <strong>with</strong> the Monte Carlo eventgener<strong>at</strong>or Sherpa [33,37,38], which provides an efficient mechanism for gener<strong>at</strong><strong>in</strong>gthe real m<strong>at</strong>rix elements and perform<strong>in</strong>g the <strong>in</strong>tegr<strong>at</strong>ion over phase space. Blackh<strong>at</strong>has been successfully applied to the calcul<strong>at</strong>ion <strong>of</strong> V +3 <strong>jets</strong> (<strong>at</strong> NLO) [126,178–181]where V is massive vector <strong>boson</strong>.The program Rocket also uses unitarity techniques to numerically gener<strong>at</strong>e oneloopamplitudes [182]. Rocket uses a numerical implement<strong>at</strong>ion <strong>of</strong> D-dimensionalunitarity [183–185], which can be applied to massive and massless particles. Thisprogram also uses the QCDLoop package [186] which calcul<strong>at</strong>es the scalar basis<strong>in</strong>tegrals. Rocket has also calcul<strong>at</strong>ed W + 3 <strong>jets</strong> [187,188] and the results betweenthe <strong>two</strong> groups are <strong>in</strong> agreement. Very recently, Rocket has been used <strong>with</strong> MCFMto compute pp → W + W + + 2j [189].In addition to the unitarity based programs described above the Helac-Phegascollabor<strong>at</strong>ion [190] have calcul<strong>at</strong>ed ttbb <strong>production</strong> and tt + 2j [191] us<strong>in</strong>g the OPPreduction technique [125,192–195]. This reduction algorithm is similar to unitaritytechniques <strong>in</strong> th<strong>at</strong> it is four-dimensional and solves for coefficients <strong>of</strong> basis <strong>in</strong>tegralsus<strong>in</strong>g on-shell constra<strong>in</strong>ts, however the OPP method can be applied equallyto products <strong>of</strong> amplitudes (as <strong>in</strong> the unitarity case) or to <strong>in</strong>dividual Feynman diagrams.The r<strong>at</strong>ional pieces are gener<strong>at</strong>ed differently however, <strong>with</strong> a separ<strong>at</strong>ion <strong>in</strong>topieces which can be gener<strong>at</strong>ed recursively and those which can be deduced from thereduction. The OPP method has also been applied to the calcul<strong>at</strong>ion <strong>of</strong> tri-<strong>boson</strong><strong>production</strong> [196,197].Efforts have also been made to autom<strong>at</strong>e 2 → 4 Feynman diagram calcul<strong>at</strong>ionsand the GOLEM collabor<strong>at</strong>ion [198, 199] has made progress <strong>in</strong> this direction, <strong>in</strong>-

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