168 research outputs found
A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
This note presents a combination of published and preliminary electroweak
results from the four LEP collaborations ALEPH, DELPHI, L3 and OPAL based on
electron-positron collision data taken at centre-of-mass energies above the
Z-pole, 130 \GeV to 209 \GeV (\LEPII), as prepared for the 2006 summer
conferences. Averages are derived for di-fermion cross sections and
forward-backward asymmetries, photon-pair, W-pair, Z-pair, single-W and
single-Z cross sections, electroweak gauge boson couplings, W mass and width
and W decay branching ratios. An investigation of the interference of photon
and Z-boson exchange is presented, and colour reconnection and Bose-Einstein
correlation analyses in W-pair production are combined. The main changes with
respect to the experimental results presented in 2005 are new preliminary
combinations of final {\LEPII} results on the mass and width of the W boson.
Including the precision electroweak measurements performed at the Z pole
published recently, the results are compared with precise electroweak
measurements from other experiments, notably CDF and D{\O}at the Tevatron.
Constraints on the input parameters of the Standard Model are derived from the
results obtained in high- interactions, and used to predict results in
low- experiments, such as atomic parity violation, M{\"o}ller scattering,
and neutrino-nucleon scattering.Comment: 173 pages; v2: Update of titlepage and addition of two reference
A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
This note presents a combination of published and preliminary electroweak
results from the four LEP collaborations and the SLD collaboration which were
prepared for the 2004 summer conferences. [...] The main changes with respect
to the experimental results presented in summer 2003 are updates to the W
branching fractions and four-fermion cross sections measured at LEP-2, and the
SLD/LEP heavy-flavour results measured at the Z pole. The results are compared
with precise electroweak measurements from other experiments, notably the final
result on the electroweak mixing angle determined in neutrino-nucleon
scattering by the NuTeV collaboration, the latest result in atomic parity
violation in Caesium, and the measurement of the electroweak mixing angle in
Moller scattering. The parameters of the Standard Model are evaluated, first
using the combined LEP electroweak measurements, and then using the full set of
high- electroweak results.Comment: 223 pages (v2: updated titlepage and correction to reference
A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
This note presents a combination of published and preliminary electroweak
results from the four LEP collaborations and the SLD collaboration which were
prepared for the 2002 summer conferences. Averages from Z resonance results are
derived for hadronic and leptonic cross sections, the leptonic forward-backward
asymmetries, the tau polarisation asymmetries, the b-bbar and c-cbar partial
widths and forward-backward asymmetries and the q-qbar charge asymmetry. Above
the Z resonance, averages are derived for di-fermion cross sections and
forward-backward asymmetries, photon-pair, W-pair, Z-pair, single-W and
single-Z cross sections, electroweak gauge boson couplings, W mass and width
and W decay branching ratios. The main changes with respect to the experimental
results presented in summer 2001 are updates to the Z-pole heavy flavour
results from SLD and LEP, and new combinations of results above the Z pole. A
new investigation of the interference of photon and Z-boson exchange is
presented. For the first time, colour reconnection and Bose-Einstein
correlation analyses in W-pair production are combined.
The results are compared with precise electroweak measurements from other
experiments, notably the recent final result on the electroweak mixing angle
determined in neutrino-nucleon scattering by the NuTeV collaboration. The
parameters of the Standard Model are evaluated, first using the combined LEP
electroweak measurements, and then using the full set of electroweak results.Comment: 216 pages; v2: add CERN EP preprint number to title page; v3: small
corrections to author list, text and reference
A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
This note presents a combination of published and preliminary electroweak
results from the four LEP collaborations and the SLD collaboration which were
prepared for the 2001 summer conferences. Averages from Z resonance results are
derived for hadronic and leptonic cross sections, the leptonic forward-backward
asymmetries, the tau polarisation asymmetries, the b-bbar and c-cbar partial
widths and forward-backward asymmetries and the q-qbar charge asymmetry. Above
the Z resonance, averages are derived for di-fermion cross sections and
forward-backward asymmetries, W-pair, Z-pair and single-W production cross
section, electroweak gauge boson couplings, W mass and width and W decay
branching ratios. For the first time, total and differential cross sections for
di-photon production are combined. The main changes with respect to the
experimental results presented in summer 2000 are updates to the Z-pole heavy
flavour results from SLD and LEP and to the W mass from LEP. The results are
compared with precise electroweak measurements from other experiments. Using a
new evaluation of the hadronic vacuum polarisation, the parameters of the
Standard Model are evaluated, first using the combined LEP electroweak
measurements, and then using the full set of electroweak results.Comment: 152 pages, minor changes to the title page onl
Combination procedure for the precise determination of Z boson parameters from results of the LEP experiments
The precise determination of the Z boson parameters from the measurements at
the Z resonance by the four collaborations ALEPH,
DELPHI, L3 and OPAL in e+e- collisions at the large electron positron
collider LEP at CERN is a landmark for precision tests of the electroweak
theory. The four experiments measured quantities which were used to extract the
mass and width of the Z boson, the hadronic cross-section at the pole of the
resonance, the ratio of hadronic and leptonic decay widths, and the leptonic
forward-backward asymmetries at the pole. The combination procedure based on
these parameters is presented in this paper.Comment: 41 pages, 4 figure
Comparison of Deep Inelastic Electron-Photon Scattering Data with the Herwig and Phojet Monte Carlo Models
Deep inelastic electron-photon scattering is studied in the Q**2 range from
1.2 to 30 GeV**2 using the LEP1 data taken with the ALEPH, L3 and OPAL
detectors at centre-of-mass energies close to the mass of the Z boson.
Distributions of the measured hadronic final state are corrected to the hadron
level and compared to the predictions of the HERWIG and PHOJET Monte Carlo
models. For large regions in most of the distributions studied the results of
the different experiments agree with one another. However, significant
differences are found between the data and the models. Therefore the combined
LEP data serve as an important input to improve on the Monte Carlo models.Comment: 38 pages, 25 figures, Submitted to Eur. Phys. J.
A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model
This note presents a combination of published and preliminary electroweak
results from the four LEP collaborations and the SLD collaboration which were
prepared for the 2000 summer conferences. Averages from Z0 resonance results
are derived for hadronic and leptonic cross sections, the leptonic
forward-backward asymmetries, the tau polarisation asymmetries, the bbbar and
ccbar partial widths and forward-backward asymmetries and the qqbar charge
asymmetry. Above the Z0 resonance, averages are derived for di-fermion cross
sections and asymmetries, W-pair, Z-pair and single-W production cross section,
electroweak gauge boson couplings and W mass and decay branching ratios. The
major changes with respect to results presented in summer 1999 are final Z0
lineshape results from LEP, updates to the W mass and gauge-boson couplings
from LEP, and ALR from SLD. The results are compared with precise electroweak
measurements from other experiments. The parameters of the Standard Model are
evaluated, first using the combined LEP electroweak measurements, and then
using the full set of electroweak results.Comment: 112 pages, 26 figure
Flavour Independent Search for Hadronically Decaying Neutral Higgs Bosons at LEP
Hadronic decays of Higgs bosons, not necessarily into b-quarks, have been
searched for using data collected at LEP-2. Such searches are complementary to
the usual Standard Model Higgs searches and lead to more model-independence.
Preliminary results obtained by the four LEP collaborations are presented for
the hZ production mechanism (using the q-qbarq-qbar, q-qbarnu-nubar and
q-qbarl+l- channels) and combined for the first time.Comment: 7 pages, 2 figures. Figures are supplied as .eps files. Sumbitted to
the EPS '01 conference in Budapest, and the Lepton-Photon '01 conference in
Rom
Searches for Invisible Higgs bosons: Preliminary combined results using LEP data collected at energies up to 209 GeV
In the year 2000 the four LEP experiments have collected data at energies
between 200 and 209 GeV, for approximately 868 pb-1 integrated luminosity. The
LEP working group for Higgs boson searches has combined these data with earlier
data sets collected at lower centre-of-mass energies to search for a neutral
CP-even Higgs boson, produced at the Standard Model rate, decaying into
"invisible" particles. No statistically significant excess has been observed
when compared to the Standard Model background prediction, and assuming that
the Higgs boson decays only into such states a lower bound has been set on its
mass at 95% confidence level of 114.4 GeV.Comment: 7 pages, 5 figures, figures supplied as .eps files. Submitted to the
EPS '01 conference in Budapest and the Lepton-Photon '01 conference in Rome.
Version 2 adds theoretical citation
Searches for the Neutral Higgs Bosons of the MSSM: Preliminary Combined Results Using LEP Data Collected at Energies up to 209 GeV
In the year 2000 the four LEP experiments collected data at centre-of-mass
energies between 200 and 209 GeV, integrating approximately 870 pb-1 of
luminosity, with about 510 pb-1 above 206 GeV. The LEP working group for Higgs
boson searches has combined these data with data sets collected previously at
lower energies. In representative scans of the parameters of the Minimal
Supersymmetric Standard Model (MSSM), the mass limits mh>91.0 GeV and mA>91.9
GeV are obtained for the light CP-even and the CP-odd neutral Higgs boson,
respectively. For a top quark mass less than or equal to 174.3 GeV, assuming
that the stop quark mixing is maximal, and choosing conservative values for
other SUSY parameters affecting the Higgs sector, the range 0.5<tanbeta<2.4 is
excluded. Additionally, the results of flavour-independent searches for
hadronically decaying Higgs bosons are included, allowing exclusion of MSSM
models with suppressed decays of the Higgs bosons to pairs of b quarks.Comment: 20 Pages, 8 figures. Submitted to EPS'01 in Budapest and
Lepton-Photon '01 in Rome. Figures supplied as .eps files, including separate
color version
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