Search for p(bar p) → WZ → lνlb(bar b) signal with the CDF experiment at Tevatron

The high energy physics has made huge steps forward the comprehension of the inner most nature of our universe and the matter we are composed of. The experimental discoveries, and the theories of the last 50 years that the experimental discoveries had confirmed or inspired, made possible to build a theory of the interactions. Weak interactions have been discovered and unified with the Electromagnetic ones in the Standard Model, which is the most widely experimentally tested and confirmed model of this century. The only prediction which is still unconfirmed is the existence of a particle, the Higgs boson, which provides particles with mass, interacting with them, in a spontaneous symmetry breakdown that doesn't violate the natural gauge symmetry of the Lagrangian of the system. One of the ways in which the Standard Model has been tested during the last 20 years is by accelerating e+e- (LEP) or p(bar p) (Tevatron) particles in a circular ring and colliding them inside a detector which is designed to reveal the final reaction products. We now have two operating hadron colliders in the world. The Tevatron at Fermilab laboratory of Chicago, collides protons against anti-protons since 1989 and has reached its maximum energy in the mass center of 1.96 TeV since 2001. It has collected approximately 7 fb-1 of data so far, that allowed important discoveries, as the top quark one, Bs mixing, precision measurements of some of the Standard Model free parameters, e.g. the W mass, and search for New Phenomena. The LHC at CERN in Geneva is a proton proton collider and has started the data acquisition in March 2010, at a center of mass energy of 7 TeV, thus beating the world record of the Tevatron. LHC however has not yet either the integrated luminosity nor the detailed understanding of the detectors to start investigating Higgs or di-boson production. The purpose of this work is to analyse the data of the CDF experiment at Tevatron to search for the associate production of a W± and Z gauge boson, looking for them in the lepton, neutrino plus jets final state, This process is predicted by the Standard Model but not revealed yet in this particular channel, both for its small cross section (σWW/WZ ∼ 16 pb-1) and for the huge backgrounds we have to deal with. The W+W- or W±Z in l (bar ν)l j j process has been measured for the first time in [4] and represents the starting point of this work. Our aim is to discriminate W±Z process from W+W- one requiring the decay of the Z boson in two b-quarks. The evidence of a peak on the invariant mass distribution will allow a tuning of the invariant mass resolution of b-jets. In addition, one of the main motivations for this quest is the similarity of this exactly predicted process with the W±H associate production signature, for which it represents a test of the searching tools and techniques, as long as an irreducible background that must be understood before such Higgs search is performed.