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Orientation ME corrections MC@NLO CKKW New Showers Underlying Event Monte Carlo Tools Frank Krauss Institute for Particle Physics Phenomenology Durham University GGI, 24.&26.9.2007 F. Krauss IPPP Monte Carlo Tools Orientation ME


  1. Orientation ME corrections MC@NLO CKKW New Showers Underlying Event Monte Carlo Tools Frank Krauss Institute for Particle Physics Phenomenology Durham University GGI, 24.&26.9.2007 F. Krauss IPPP Monte Carlo Tools

  2. Orientation ME corrections MC@NLO CKKW New Showers Underlying Event Topics of the lectures Lecture 1: Tour through Event Generators 1 Hard physics simulation: Parton Level event generation Dressing the partons: Parton Showers Soft physics simulation: Hadronization Beyond factorization: Underlying Event Lecture 2: Higher Orders in Monte Carlos 2 Some nomenclature: Anatomy of HO calculations Merging vs. Matching Thanks to the other Sherpas: T.Gleisberg, S.H¨ oche, S.Schumann, F.Siegert, M.Sch¨ onherr, J.Winter; other MC authors: S.Gieseke, K.Hamilton, L.Lonnblad, F.Maltoni, M.Mangano, P.Richardson, M.Seymour, T.Sjostrand, B.Webber, . . . . F. Krauss IPPP Monte Carlo Tools

  3. Orientation ME corrections MC@NLO CKKW New Showers Underlying Event Simulation’s paradigm Basic strategy Sketch of an event Divide event into stages, separated by different scales. ������ ������ ����� ����� ������ ������ ������ ������ ����� ����� ����� ����� ������ ������ ����� ����� ����� ����� ������ ������ ����� ����� ������ ������ ����� ����� ����� ����� ������ ������ ����� ����� ����� ����� ������ ������ ����� ����� ����� ����� ��� ��� Signal/background: ������ ������ ������ ������ ����� ����� ������ ������ ��� ��� ������ ������ ����� ����� ������ ������ ������ ������ ��� ��� ������ ������ ������ ������ ��� ��� ������ ������ ����� ����� ������ ������ ��� ��� ����� ����� ��� ��� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ���� ��� ���� ���� ��� ���� ���� ���� ���� ��� ��� ���� ���� �� �� �� �� Exact matrix elements. ��� ��� �� �� �� �� ��� ��� �� �� ��� ��� �� �� ��� ��� �� �� �� �� �� �� �� �� ��� ��� ��� ��� ��� ��� ��� ��� �� �� ��� ��� ��� ��� ��� ��� �� �� ��� ��� ��� ��� �� �� ��� ��� ��� ��� �� �� QCD-Bremsstrahlung: ��� ��� ��� ��� �� �� ��� ��� �� �� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ����� ����� ����� ����� ��� ��� ����� ����� ����� ����� ��� ��� ��� ��� ����� ����� ��� ��� ����� ����� ����� ����� ��� ��� ��� ��� ��� ��� ����� ����� ����� ����� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� Parton showers (also in initial state). ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� �� �� ��� ��� ��� ��� ��� ��� ��� ��� �� �� ��� ��� ��� ��� �� �� ��� ��� ��� ��� ��� ��� �� �� ��� ��� ��� ��� �� �� ��� ��� ��� ��� �� �� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� Multiple interactions: ��� ��� ��� ��� ��� ��� �� �� �� �� �� �� ��� ��� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� ��� ��� ��� ��� �� �� Beyond factorization: Modeling. ��� ��� �� �� ��� ��� ��� ��� ��� ��� ���� ���� ��� ��� ���� ���� ��� ��� ���� ���� ���� ���� ��� ��� ��� ��� ���� ���� ��� ��� ���� ���� ����� ����� ����� ����� ������ ������ ����� ����� ����� ����� ����� ����� ������ ������ ����� ����� Hadronization: ����� ����� ����� ����� ������ ������ ����� ����� ����� ����� ����� ����� ����� ����� ����� ����� Non-perturbative QCD: Modeling. F. Krauss IPPP Monte Carlo Tools

  4. Orientation ME corrections MC@NLO CKKW New Showers Underlying Event Today’s lecture: Higher Orders in Monte Carlos Which higher orders? Some anatomy First attempts: ME corrections Higher orders in rate: MC@NLO Higher orders through extra emission: Merging A new shower formulation F. Krauss IPPP Monte Carlo Tools

  5. Orientation ME corrections MC@NLO CKKW New Showers Underlying Event Higher Orders Nomenclature Specifying higher-order corrections: γ ∗ → hadrons In general: N n LO ↔ O ( α n s ) But: only for inclusive quantities (e.g.: total xsecs like γ ∗ → hadrons) . Counter-example: thrust distribution In general, distributions are HO. Distinguish real & virtual emissions: Real emissions → mainly distributions, virtual emissions → mainly normalization. F. Krauss IPPP Monte Carlo Tools

  6. Orientation ME corrections MC@NLO CKKW New Showers Underlying Event Higher Orders Nomenclature Anatomy of HO calculations: Virtual and real corrections NLO corrections: O ( α s ) Virtual corrections = extra loops Real corrections = extra legs UV-divergences in virtual graphs → renormalization But also: IR-divergences in real & virtual contributions Must cancel each other, non-trivial to see: N vs. N + 1 particle FS, divergence in PS vs. loop F. Krauss IPPP Monte Carlo Tools

  7. Orientation ME corrections MC@NLO CKKW New Showers Underlying Event Higher Orders Nomenclature Cancelling the IR divergences: Subtraction method Total NLO xsec: � d D k |M| 2 � d 4 k |M| 2 σ NLO = σ Born + V + R IR div. in real piece → regularize: d 4 k |M| 2 d D k |M| 2 � � R → R Construct subtraction term with same IR structure: d D k ( |M| 2 R − |M| 2 d 4 k |M| 2 � � S ) = RS = finite. d D k | ˜ S| 2 , universal | ˜ � d D k |M| 2 � S| 2 . Possible: S = σ Born S| 2 = finite (analytical) d D k | ˜ � d D k |M| 2 � V + σ Born F. Krauss IPPP Monte Carlo Tools

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