Senior Thesis
A Search for the Z′ Boson in the Dimuon Decay Channel at ATLAS
Siyuan Sun
April 2011
Thesis Committee: Ashutosh Kotwal (Advisor), Stephen Teitsworth, Ayana Arce, Henry Greenside
ABSTRACT:
This analysis searches for the Z′ boson at the Large Hadron Collider with data collected by the ATLAS detector in 2010. The Z′ particle is predicted to exist by nearly all Grand Unification Theories. Just as electricity and magnetism are actually two manifestations of one force, Grand Unification Theories attempt to unify three of the fundamental forces of the universe, electrodynamics, the strong nuclear force, and the weak force into one coherent description. To many, the Grand Unification Theories represent the next, still unconfirmed level, in our understanding of fundamental physics. Discovery of the Z′ boson would provide evidence in support of Grand Unification Theories.
This analysis will search for an unaccounted-for peak in the combined mass of a pair of oppositely charged muons. The Z′ boson can decay into a pair of oppositely charged muons. The two muons are measured by the ATLAS detector at CERN and the original Z′ boson can be reconstructed from these measurements. We also study processes that mimic Z′ production and determine the accuracy of the ATLAS detector’s measurements.
We found no disagreement between the data and expected backgrounds. No Z ′ bosons 1
were observed. We proceeded to set limits on the maximum number of Z′ bosons that could have existed but were not detected due to chance.
For each Z′ mass, different Z′ models predict different amounts of Z′ bosons. By comparing the limits on the number of Z′ bosons with the predicted number of Z′ bosons, we set lower limits on the mass of the Z′ boson for several Z′ models. The lower limit of the Sequential Standard Model Z′ mass is 833 GeV. The lower limits of the six E6 motivated Z′ masses range from 646 GeV to 736 GeV. If the Z′ boson exists and is of the formed predicted by one of the models, its mass will be greater than the mass listed. All exclusion limits are made at the 95% confidence level.
Here is the complete thesis in PDF: Sun Thesis