47 research outputs found
Renormalizability and model independent description of Z' signals at low energies
Model independent search for signals of heavy Z' gauge bosons in low-energy
four-fermion processes is analyzed. It is shown that the renormalizability of
the underlying theory containing Z', formulated as a scattering in the field of
heavy virtual states, can be implemented in specific relations between
different processes. Considering the two-Higgs-doublet model as the low-energy
basis theory, the two types of Z' interactions with light particles are found
to be compatible with the renormalizability. They are called the Abelian and
the "chiral" couplings. Observables giving possibility to uniquely detect Z' in
both cases are introduced.Comment: 11 pages, 5 figures, RevTeX. The text of the paper is rewritten to be
more clear and precis
Signals of Z' boson in the Bhabha process within the LEP2 data set
The LEP2 data set on the Bhabha process is analyzed with the aim to detect
the signals of the heavy virtual Z' gauge bosons. The state interacting with
the left-handed standard-model doublets and called the Chiral Z' is
investigated. This particle was introduced already as the low-energy state
allowed by the renormalizability of the model. The contribution of the Chiral
Z' state to the Bhabha process is described by two parameters: the coupling to
electrons and the Z-Z' mixing angle. The sign-definite one-parameter observable
is proposed to measure the Z' coupling to the electron current. The
one-parameter fit of the data shows no signals of the particle. The alternative
two-parameter fit of the differential cross-sections is also performed. It also
shows no Chiral Z' signals. The comparisons with other fits are discussed.Comment: 15 pages, 4 figures. The paper was completely rewritten on the base
of new dat
Model-independent search for the Abelian Z' boson in the Bhabha process
Model-independent observables to pick out the Abelian Z' signal in the Bhabha
process are introduced at energies >= 200 GeV. They measure separately the
Z'-induced vector and axial-vector four-fermion contact couplings. The analysis
of the LEP2 data constrains the value of the Z'-induced vector four-fermion
coupling at the 2-sigma confidence level that corresponds to the Abelian Z'
boson with the mass of order 1 TeV.Comment: 7 pages, 5 figures, uses RevTeX4. The text of the paper is completely
rewritte
Z' signal from the LEP2 data
The many-parametric fit of the LEP2 data on e^+e^-\to e^+e^-, \mu^+\mu^-,
\tau^+\tau^- processes is performed to estimate signals of the Abelian Z'-boson
beyond the standard model. The model-independent relations between the Z'
couplings to the standard model particles allow to describe the Z' effects in
lepton processes by 4 independent parameters. No signal is found by the
complete LEP2 data set, and the 1.3\sigma signal is detected by the fit of the
backward bins. The Z' couplings to the vector and axial-vector lepton currents
are constrained. The comparisons with the one-parameter fits and with the LEP1
experiments are performed.Comment: 6 pages, 2 figures, RevTeX. The paper was completely rewritten. The
errors in the first version were eliminated. The comparison with the LEP1
data is adde