Göttingen 2012 – scientific programme

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T: Fachverband Teilchenphysik

T 28: QCD mit schweren Eichbosonen 2

T 28.6: Talk

Thursday, March 1, 2012, 18:00–18:15, ZHG 009

Data driven estimate of the hadronic recoil in W events with the ATLAS detector — •Giovanni Siragusa — Julius-Maximilians-Universität, Würzburg, Deutschland

In W boson semi-leptonic decays, the reconstruction of the kinematic of the event is complicated by the presence of the neutrino that escapes the detection. On the other hand, the measurement with a high degree of accuracy of fundamental SM parameters, like the W mass, requires a proper knowledge of the event kinematic.
In order to reduce the systematic uncertainties associated to a non perfect MC simulation, a data driven technique was developed. It relies on the assumption that, for a given event topology, the level of hadronic activity is similar between W and Z events.
The hadrons recoiling against a boson (the so called hadronic recoil) have to balance the boson transverse momentum. In particular, in Z boson decays it is possible to parametrise the distribution of the hadronic recoil in terms of the boson transverse momentum (p_T) and of the total transverse momentum in the event. The resolution functions obtained in this way can be used to smear the W recoil at MC-truth level, without relying explicitly on detector simulations. The method will be illustrated together to the measurement of the W transverse momentum with the ATLAS detector. Further improvements, that are foreseen in view of the measurement of the W mass, will be also shown.