1 / 10

Precision tools for QCD: scale separation and multi-loop diagrams

Precision tools for QCD: scale separation and multi-loop diagrams. West Coast LHC Theory Network February 2006. Andrzej Czarnecki University of Alberta. Separation of scales and dimensional regularization : a simple example. Suppose we can’t compute this: expand.

Download Presentation

Precision tools for QCD: scale separation and multi-loop diagrams

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Precision tools for QCD:scale separation and multi-loop diagrams West Coast LHC Theory Network February 2006 Andrzej Czarnecki University of Alberta

  2. Separation of scalesand dimensional regularization: a simple example Suppose we can’t compute this: expand

  3. Recurrence relations: integration by parts Result: recurrence relations like

  4. How does b quark decay? Semileptonic Semileptonic branching ratio (parton model without QCD) Nonleptonic 8% shift of the NL width shiftsBSLby 0.6 percentage points

  5. Missing in the theoretical bound:NNLO corrections to non-leptonic decays. Example: c b g g u d Four loop diagrams with masses – the limit of what has been done in QFT so far (only numerical for g-2) Our approach: reduction via recurrence; analytical determination of “master diagrams”

  6. Results Example for a single diagram: (with Maciek Ślusarczyk) Total correction for the non-leptonic width: About 5-8% increase of the NL width; lowers the theoretical lower bound on BSL

  7. Outlook • Methods of scale separation, recurrence relations, large-scale symbolic computation are versatile. • Progress in several areas: • New electron mass determination • Establishment of the running of the weak angle; • Solution of the b-decay branching puzzle. • Next challenge: QCD factorization for the LHC.

  8. What do experiments get for BSL? World average: hep-ex/0505100 Theoretical lower limit: Bigi et al, 1994 Voloshin, 2000 2.6σ difference Vbc = 0.04 << 1 Standard Model suppressed: good place to look for New Physics

  9. Known two-loop corrections on the bc line first calculation (1996) latest one (2004) mb (1) (mW/mt)2 = 0.2 mW/mb e b c Zero recoil line n Leptons’ invariant mass q – quark mass mc/mb mb (1)

  10. Summary of b decays: • “Fair agreement” reached between theory and experiment; • More important: we can further improve the theoretical prediction (account for charm mass); • With new data forthcoming, we want to use the branching ratio to help discover competitors to W bosons.

More Related