Search for techniparticles at D0 Run II

Abstract

Technicolor theory (TC) accomplishes the necessary electroweak symmetry breaking responsible for the mass of the elementary particles. TC postulates the existence of a new SU(N{sub TC}) gauge theory. Like QCD the exchange of gauge bosons causes the existence of a non-vanishing chiral condensate which dynamically breaks the SU(N{sub TC}){sub L} x SU(N{sub TC}){sub R} symmetry. This gives rise to N{sub TC}{sup 2}-1 Nambu-Goldstone Bosons. Three of these Goldstone Bosons become the longitudinal components of the W{sup {+-}} and Z which therefore acquire mass; the remaining ones are new particles (technihadrons) that can be produced at the high energy colliders and detected. The Technicolor Straw Man Model (TCSM) is a version of the dynamical symmetry breaking with a large number of technifermions and a relative low value of their masses. One of the processes predicted by the TCSM is q{bar q} {yields} V{sub T} {yields} W{pi}{sub T}, where V{sub T} is the Technicolor equivalent of the QCD vector meson and {pi}{sub T} is the equivalent of the pion. W is the electroweak gauge boson of the Standard Model. This dissertation describes the search for W{pi}{sub T} with the D0 detector, a multi-purpose particle detector located at one of the collision pointsmore » of the Tevatron accelerator situated in Batavia, IL. The final state considered for this thesis is a W boson that decays to electron and neutrino plus a {pi}{sub T} that decays into b{bar c} or b{bar b}, depending on the charge of the initial technivector meson produced. In the D0 detector this process will appear as a narrow cluster of energy deposits in the electromagnetic calorimeter with an associated track reconstructed in the tracking detector. The undetected neutrino from the decay of the W boson will be seen as missing momentum. The fragmentation of the quarks from the decay of the {pi}{sub T} will produce two jets of collimated particles. Events where a b-quark is produced are selected by requesting at least one jet to be associated with a secondary vertex of interaction produced by the decay of B-meson (b-tagging). In the absence of an excess over the Standard Model prediction for the final state considered in this analysis, we compute a 95% Confidence Level upper limit on the techniparticle production cross section for the V{sub T} mass range: 190 GeV/c{sup 2} {le} m(V{sub T} ) {le} 220 GeV/c{sup 2}.« less