21,419 research outputs found
Experimental Results on Two-Photon Physics from LEP
This review covers selected results from the LEP experiments on the structure
of quasi-real and virtual photons.
The topics discussed are the total hadronic cross-section for photon-photon
scattering, hadron production, jet cross-sections, heavy quark production for
photon-photon scattering, photon structure functions, and cross-sections for
the exchange of two virtual photons.Comment: 13 pages, 11 figures, to appear in Proceedings of the Ringberg
Workshop 'New Trends in HERA Physics' 1999, May 30 - June 4, 199
Precision Physics at LEP
1 - Introduction
2 - Small-Angle Bhabha Scattering and the Luminosity Measurement
3 - Z^0 Physics
4 - Fits to Precision Data
5 - Physics at LEP2
6 - ConclusionsComment: Review paper to appear in the RIVISTA DEL NUOVO CIMENTO; 160 pages,
LateX, 70 eps figures include
QED challenges at FCC-ee precision measurements
The expected experimental precision of the rates and asymmetries in the
Future Circular Collider with electron positron beams (FCC-ee) in the centre of
the mass energy range 88-365GeV considered for construction in CERN, will be
better by a factor 5-200. This will be thanks to very high luminosity, factor
up to higher than in the past LEP experiments. This poses the
extraordinary challenge of improving the precision of the Standard Model
predictions by a comparable factor. In particular the perturbative calculations
of the trivial QED effects, which have to be removed from the experimental
data, are considered to be a major challenge for almost all quantities to be
measured at FCC-ee. The task of this paper is to summarize on the "state of the
art" in this class of the calculations left from the LEP era and to examine
what is to be done to match the precision of the FCC-ee experiments -- what
kind of technical advancements are necessary. The above analysis will be done
for most important observables of the FCC-ee like the total cross sections near
and threshold, charge asymmetries, the invisible width of boson,
the spin asymmetry from lepton decay and the luminosity measurement.Comment: Corrected author's name in ref. [106
ANOMALOUS GAUGE BOSON INTERACTIONS
We discuss the direct measurement of the trilinear vector boson couplings in
present and future collider experiments. The major goals of such experiments
will be the confirmation of the Standard Model (SM) predictions and the search
for signals of new physics. We review our current theoretical understanding of
anomalous trilinear gauge boson self-interactions. If the energy scale of the
new physics is TeV, these low energy anomalous couplings are expected
to be no larger than . Constraints from high precision
measurements at LEP and low energy charged and neutral current processes are
critically reviewed.Comment: 53 pages with 17 embedded figures, LaTeX, uses axodraw.sty, figures
available on request. The complete paper, is available at
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-871.ps.Z or
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-871.ps.Z Summary
of the DPF Working Subgroup on Anomalous Gauge Boson Interactions of the DPF
Long Range Planning Stud
Isolated Lepton Production at Colliders
The production of isolated leptons with high transverse momentum in high
energy e-e, p-p or e-p collisions is reviewed. The leptons are produced either
through boson splitting or by boson-boson collision and yield experimentally
simple and spectacular topologies which can be exploited to validate the
Standard Model or to search for new phenomena.Comment: 50 page
The Higgs puzzle: experiment and theory
The present experimental and theoretical knowledge of the physics of
electroweak symmetry breaking is reviewed. Data still favor a light Higgs
boson, of a kind that can be comfortably accommodated in the Standard Model or
in its Minimal Supersymmetric extension, but exhibit a non-trivial structure
that leaves some open questions. The available experimental information may
still be reconciled with the absence of a light Higgs boson, but the price to
pay looks excessive. Recent theoretical ideas, linking the weak scale with the
size of possible extra spatial dimensions, are briefly mentioned. It is
stressed once more that experiments at high-energy colliders, such as the
Tevatron and the LHC, are the crucial tool for eventually solving the Higgs
puzzle.Comment: 18 pages, 13 figures, invited talk at the 20th International
Symposium on Lepton and Photon Interactions at High Energies (Lepton Photon
01), Rome, Italy, 23-28 July 200
Invisible Z-Boson Decays at e+e- Colliders
The measurement of the invisible Z-boson decay width at e+e- colliders can be
done "indirectly", by subtracting the Z-boson visible partial widths from the
Z-boson total width, or "directly", from the process e+e- -> \gamma \nu
\bar{\nu}. Both procedures are sensitive to different types of new physics and
provide information about the couplings of the neutrinos to the Z-boson. At
present, measurements at LEP and CHARM II are capable of constraining the
left-handed Z\nu\nu-coupling, 0.45 <~ g_L <~ 0.5, while the right-handed one is
only mildly bounded, |g_R| <= 0.2. We show that measurements at a future e+e-
linear collider at different center-of-mass energies, \sqrt{s} = MZ and
\sqrt{s}s ~ 170 GeV, would translate into a markedly more precise measurement
of the Z\nu\nu-couplings. A statistically significant deviation from Standard
Model predictions will point toward different new physics mechanisms, depending
on whether the discrepancy appears in the direct or the indirect measurement of
the invisible Z-width. We discuss some scenarios which illustrate the ability
of different invisible Z-boson decay measurements to constrain new physics
beyond the Standard Model
Eleven Years of QCD at LEP
Studies of hadronic final states of annihilations, observed at the
Large Electron Positron Collider LEP at CERN, are reviewed. The topics included
cover measurements of , hadronic event shapes and hadronisation
studies, tests of asymptotic freedom and of the non-Abelian gauge structure of
QCD, differences between quark and gluon jets, tests of power corrections and
selected results of two-photon scattering processes. The improvements obtained
at LEP are demonstrated by comparing to results from the pre-LEP era. This
article consists of a reproduction of slides presented at the LEPFest in
October 2000, supplemented by a short descriptive text and a list of relevant
references.Comment: 10 pages of text plus reproduction of 27 transparencies presented at
the LEPFest at CERN, October 2000. To be published in Eur. Phys. Jour
(direct) C; a higher resolution version of the viewgraphs can be obtained
from: http://www.mppmu.mpg.de/~bethke/LEPQCDtalk-higres.pd
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