Physics (Internal)

A Search for Technicolor at the Large Hadron Collider

This event is part of the PhD Final Oral Exams.

Dissertation Committee:  John Butler, Kevin Black, Robert Carey (Chairman), Kenneth Lane and William Skocpol Abstract: The Standard Model of particle physics provides an accurate description of all experimental data to date. The only unobserved piece of the Standard Model is the Higgs boson, a consequence of the spontaneous breaking of electroweak symmetry by the Higgs mechanism. An alternative to the Higgs mechanism is proposed by Technicolor theories which break electroweak symmetry dynamically through a new force. Technicolor predicts many new particles, called Technihadrons, that could be observed by experiments at hadron colliders. This thesis presents a search for two of the lightest Technihadrons, the ρT and ωT. The Low-Scale Technicolor model predicts the phenomenology of these new states. The ρT and ωT are produced through quark anti-quark annihilation and couple to Standard Model fermions through the Drell-Yan process, which can result in the dimuon final state. The ρT and ωT preferentially decay to the πT and a Standard Model gauge boson if kinematically allowed. Changing the mass of the πT relative to that of the ρT and ωT affects the cross section times branching fraction to dimuons. The ρT and ωT are expected to have masses below about 1 TeV. The Large Hadron Collider (LHC) at CERN outside of Geneva, Switzerland, produces proton-proton collisions with a center of mass energy of 7 TeV. A general purpose high energy physics detector ATLAS has been used in this analysis to search for Technihadrons decaying to two muons. We use the ATLAS detector to reconstruct the tracks of muons with high transverse momentum coming from these proton-proton collisions. The dimuon invariant mass spectrum is analyzed above 130 GeV to test the consistency of the observed data with the Standard Model prediction. We observe excellent agreement between our data and the background only hypothesis, and proceed to set limits on the cross section times branching ratio of the ρT and ωT as a function of their mass using the Low-Scale Technicolor model. We combine the dielectron and dimuon channels to exclude masses of the ρT and ωT between       130 GeV – 480 GeV at 95% Confidence Level for masses of the πT between 50 GeV – 480 GeV. In addition for the parameter choice of  m(πT) = m(ρT/ωT) – 100 GeV, 95% Confidence Level limits are set excluding masses of the ρT and ωT below      470 GeV. This analysis represents the current world's best limit on this model.