Doctoral Dissertation Open Access

Search for Diboson Resonances in the All-Hadronic Final State with the CMS Detector

Schäfer, Daniela

Thesis supervisor(s)

Mozer, Matthias; Müller, Thomas

A search for new resonances decaying to WW, WZ or ZZ in the all hadronic final state using
77.3 fb −1 of data taken with the CMS experiment at the CERN LHC at a center-of-mass
energy of 13 TeV is presented. The search focuses on potential new particles with a mass
at the TeV scale resulting in a high transverse momentum of the produced vector bosons.
The subsequent decay products of the vector bosons are therefore highly collimated and
reconstructed into a single large-radius jet, which are further classified using jet substructure
methods. The analysis presented utilizes a new data-driven background modeling technique
based on a template fit in a three-dimensional hyperspace spanned by the dijet invariant mass
and the corrected jet masses of the two final state jets. This method allows the utilization of
the full available signal yield while simultaneously constraining the background processes by
including the mass sideband regions in the fit. This grants the opportunity to easily expand
this framework to include VH, HH or more exotic signals with different messenger particles
in the future.
No significant excess is observed above the estimated standard model background and limits
are set at 95% confidence level on the cross section times branching fraction of a new particle,
which are interpreted in terms of various models that predict spin-2 gravitons or spin-1 vector
bosons. In a heavy vector triplet model, spin-1 Z' and W' resonances with masses below
3.5 and 3.8 TeV, respectively, are excluded at 95% confidence level. In a narrow-width bulk
graviton model, upper limits on cross sections times branching fractions are set between 27
and 0.2 fb for resonance masses between 1.2 and 5.2 TeV, respectively. The limits presented
in this thesis are the best to date in the dijet final state.

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