Electroweak corrections for W/Z+ n jet production

by Sasha Turczyk (LBL Berkeley)

Friday 20 Jul 2012, 14:00 → 15:00 Europe/Berlin

3344 (Physikdepartment)

In the era of the LHC experiments the analysis of vector boson together with n-jet production becomes very important. On the one hand these processes serve as a testing environment for perturbative QCD calculations as well as detector understanding. On the other hand, W/Z + n jet production is used for new physics searches and thus one has to deal with a huge amount of irreducible Standard Model back ground. Therefore we need to understand these processes thoroughly. With the increasing center of mass energy S, electroweak corrections become more important. Especially Sudakov type logarithms of the form αew ln2 [MW/Z /p2 W/Z ] can appear and potentially T become large in the differential cross section. These logarithms stem from infrared and collinear divergences for M → 0, as e.g. in QCD and QED processes involving a real gluon or photon emission, regularized by the finite gauge boson mass. I will review the general methods presented in [1–3] and extend them to re-sum the electroweak and QCD logarithms of W/Z + 1 jet production explicitly as well as discuss the necessary input to generalize the computation to n jets. The starting point for this analysis is the unbroken full Standard Model, which is matched onto a SCET like theory SCETEW to describe all particles as collinear fields. At M ∼ 100 GeV the electroweak symmetry is broken and SCETEW is consequently matched onto SCETγ , in which the heavy gauge bosons as well as the top quark are integrated out and remain as static “boosted HQET” fields. This approach allows to compute the anomalous dimension for the running between the high and low scale as well as low scale matching, including the effects of symmetry breaking, systematically for each process. The soft degrees of freedom can interact between different particles and depend on the gauge quantum numbers, only. The collinear degrees of freedom instead do not interact with each other which actually depends on the regulator choice - and thus depend only on the type of the particle. Therefore we obtain both soft and collinear corrections. In turn we are able to re-sum the logarithms between the high scale at the center of mass energy and the low scale at which the symmetry is broken using the anomalous dimension and additionally obtain the low scale matching corrections at the same time. This correction can be computed analytically as the Wilson coefficient matrix for the operator basis at the low scale up to NLL precision. I outline the automizable (numerical) calculation as well as necessary input for a general process. Then I will discuss the specific W/Z + 1 jet production and changes to several observables due to this corrections, especially I will mention the importance for distinguished analysis. The analysis includes the effects of parton distribution functions of the initial state protons. The possible generalization to more final state vector bosons and jets is discussed in the end. These results will be important to match the theoretical prediction to an experimental analysis. Some ideas to treat these issues are briefly examined. [1] J. -y. Chiu, F. Golf, R. Kelley and A. V. Manohar, Phys. Rev. Lett. 100 (2008) 021802 [arXiv:0709.2377 [hep-ph]]. [2] J. -y. Chiu, F. Golf, R. Kelley and A. V. Manohar, Phys. Rev. D 77 (2008) 053004 [arXiv:0712.0396 [hep-ph]]. [3] J. -y. Chiu, A. Fuhrer, R. Kelley and A. V. Manohar, Phys. Rev. D 81 (2010) 014023 [arXiv:0909.0947 [hep-ph]].