20 research outputs found
Production of Single W Bosons at LEP
We report on the observation of single W boson production in a data sample collected by the L3 detector at LEP2. The signal consists of large missing energy final states with a single energetic lepton or two hadronic jets. The cross-section is measured to be at the centre of mass energy \sqrt{s}=172 \GeV{}, consistent with the Standard Model expectation. From this measurement the following limits on the anomalous WW gauge couplings are derived at 95\% CL: and
Measurement of the Average Lifetime of b-Hadrons in Z Decays
We present a measurement of the average b-hadron lifetime at the collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of using the impact parameter of leptons with high momentum and high transverse momentum. The combined result is \begin{center} . \end{center} In addition, we measure the average charged b-decay multiplicity and the normalized average b-energy at LEP to be \begin{center} , \end{center} \begin{center} \end{center
The neutron and its role in cosmology and particle physics
Experiments with cold and ultracold neutrons have reached a level of
precision such that problems far beyond the scale of the present Standard Model
of particle physics become accessible to experimental investigation. Due to the
close links between particle physics and cosmology, these studies also permit a
deep look into the very first instances of our universe. First addressed in
this article, both in theory and experiment, is the problem of baryogenesis ...
The question how baryogenesis could have happened is open to experimental
tests, and it turns out that this problem can be curbed by the very stringent
limits on an electric dipole moment of the neutron, a quantity that also has
deep implications for particle physics. Then we discuss the recent spectacular
observation of neutron quantization in the earth's gravitational field and of
resonance transitions between such gravitational energy states. These
measurements, together with new evaluations of neutron scattering data, set new
constraints on deviations from Newton's gravitational law at the picometer
scale. Such deviations are predicted in modern theories with extra-dimensions
that propose unification of the Planck scale with the scale of the Standard
Model ... Another main topic is the weak-interaction parameters in various
fields of physics and astrophysics that must all be derived from measured
neutron decay data. Up to now, about 10 different neutron decay observables
have been measured, much more than needed in the electroweak Standard Model.
This allows various precise tests for new physics beyond the Standard Model,
competing with or surpassing similar tests at high-energy. The review ends with
a discussion of neutron and nuclear data required in the synthesis of the
elements during the "first three minutes" and later on in stellar
nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic
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Search for (B-L) Nonconservation in Neutron-Antineutron Transitions
Proton decay into (B - L) conserving modes with rates predicted by the original SU(5) grand unification scheme was not experimentally observed. An alternative possibility for baryon instability corresponding to the nonconservation of (B - L) and evolving at the intermediate energy scale needs to be explored in new experiments. One of the most spectacular manifestations of the physics of such an energy scale would be the observation of neutron antineutron transitions. Future prospects and discovery potentials of an n{yields}{anti n} search are discussed here
Single and multi-photon events with missing energy in e(+)e(-) collisions at 161 GeV <root s < 172 GeV
Contains fulltext :
26276.pdf (publisher's version ) (Open Access
Measurement of inclusive omega and eta' production in hadronic Z decays
Contains fulltext :
26257.pdf (publisher's version ) (Open Access
Evidence for Gluon Interference in Hadronic Z-Decays
Contains fulltext :
26227.pdf (publisher's version ) (Open Access
One-Prong Tau-Decays with Neutral Kaons
Contains fulltext :
26231.pdf (publisher's version ) (Open Access