15 research outputs found

### Theoretical and phenomenological aspects of vector boson production

The production of three gauge bosons in high-energy collisions - in particular in view of a next-linear collider with center of mass energies in the TeV range - offers an unique opportunity to probe the Standard Model (SM) of today's particle physics. In this thesis we pay particular attention to the electroweak sector of the theory. We investigate the gauge structure {i. e. possible deviations from the SM predictions of gauge boson self-interactions manifest e. g. in anomalous quartic gauge boson couplings and Radiation zeros) as well as electroweak radiative corrections in order to improve theoretical predictions for SM processes. Quartic gauge boson couplings can be regarded as a direct window on the sector of electroweak symmetry breaking. We have studied the impact of three such anomalous couplings on the processes e+e(^-) â†’ WWÎ³, ZZÎ³ and ZÎ³Î³ at LEP2 and a future linear collider. In certain high-energy scattering processes involving charged particles and the emission of one or more photons, the scattering amplitude vanishes for particular configurations of the final state particles. The fact that gauge symmetry is a vital ingredient for the cancellation to occur means that radiation zeros can be used to probe physics beyond the standard model. For example anomalous electroweak gauge boson couplings destroy the delicate cancellation necessary for the zero to occur. We have studied the process qq â†’ WWÎ³. To match the expected experimental precision at future linear colliders, improved theoretical predictions beyond next-to-leading order are required. By choosing an appropriate gauge, we have developed a formalism to calculate such corrections for arbitrary electroweak processes. As an example we consider here the processes e(^+)e â†’ f f and e(^+)e(^-) â†’ W(^+)(_T)W(^-)(_T), W(^+)(_L)W(^-)(_L) and study the perturbative structure of the electroweak Sudakov logarithms by means of an explicit two-loop calculation. In this way we investigate how the Standard Model, with its mass gap between the photon and Z boson in the neutral sector, compares to unbroken theories like QED and QCD. We observe that the two-loop corrections are consistent with an exponentiation of the one-loop corrections. In this sense the Standard Model behaves like an unbroken theory at high energies

### Anomalous Quartic Couplings in $\nu \bar{\nu} \gamma \gamma$ Production via WW-Fusion at LEP2

The production of $\nu \bar{\nu} \gamma \gamma$ in high-energy $e^+e^-$
collisions offers a window on anomalous quartic gauge boson couplings. We
investigate the effect of two possible anomalous couplings on the cross section
for $\nu \bar{\nu} \gamma \gamma$ production via $WW$-fusion at LEP2 ($\sqrt{s}
= 200$ GeV).Comment: 7 pages, 3 figures, LaTex, clarifying definition adde

### Energy Spectrum of Leptons from $e^+e^- \to W^+W^-$ in the Presence of Strong W^+_LW^-_L Interaction

The energy spectrum of leptons, produced by the decay of one or both W's in
the reaction $e^+e^- \to W^+W^-$, is a significant probe of the helicity
structure of this process. We calculate the energy spectrum $d \sigma /d E$ of
a single decay lepton, as well as the two-dimensional energy distribution $d
\sigma/d E_+dE_-$. We then consider a possible strong final state interaction
in the longitudinally polarized state of the W^+W^- system, parametrized by a
\rho -like resonance in the region of 1.8 TeV. We show that such a resonance
produces measurable effects in the lepton spectrum at $\sqrt{s}=500$ GeV. The
results are compared with those obtained from a non-resonant interaction
approximated by a phase factor $e^{i \delta}$ in the l=1 part of the W^+_LW^-_L
amplitude.Comment: LaTeX, 12 pages including 3 eps figures, uses amssym and eps

### Radiation Zeros in W^+W^-\gamma Production at High-Energy Colliders

The vanishing of the cross section for particular points in phase space -
radiation zeros - is examined for the process $q \bar q \to W^+W^- \gamma$ at
high energy. Unlike the process $q \bar q' \to W^\pm \gamma$, actual zeros only
occur in the soft-photon limit. However, for photon energies that are not too
large, the cross section does exhibit deep dips in regions of phase space
corresponding to the position of the actual zeros. We show that in these
regions the sensitivity to possible anomalous quartic couplings is very large.Comment: 19 pages, 7 figures, LaTe