4,768 research outputs found
Search for Higgs and New Phenomena at Colliders
The present status of searches for the Higgs boson(s) and new phenomena is
reviewed. The focus is on analyses and results from the current runs of the
HERA and Tevatron experiments. The LEP experiments have released their final
combined MSSM Higgs results for this conference. Also included are results from
sensitivity studies of the LHC experiments and lepton flavour violating
searches from the B factories, KEKB and PEP-II.Comment: XXII International Symposium on Lepton-Photon Interactions at High
Energy (11 pages, 16 figures, 2 tables
Strong Coupling Constant from the Photon Structure Function
We extract the value of the strong coupling constant alpha_s from a
single-parameter pointlike fit to the photon structure function F_2^gamma at
large x and Q^2 and from a first five-parameter full (pointlike and hadronic)
fit to the complete F_2^gamma data set taken at PETRA, TRISTAN, and LEP. In
next-to-leading order and the MSbar renormalization and factorization schemes,
we obtain alpha_s(m_Z)=0.1183 +/- 0.0050(exp.)^+0.0029_-0.0028(theor.)
[pointlike] and alpha_s(m_Z)=0.1198 +/- 0.0028(exp.)^+0.0034_-0.0046(theor.)
[pointlike and hadronic]. We demonstrate that the data taken at LEP have
reduced the experimental error by about a factor of two, so that a competitive
determination of alpha_s from F_2^gamma is now possible.Comment: 11 pages, 2 tables, 2 figures. Version accepted for publication by
Phys. Rev. Let
Possible improvements on the mass of the tau neutrino using leptonic decays
We show how a very accurate measurement of the branching ratios of the
leptonic decay modes of the mesons can lead to a significant
improvement in the mass limit for the tau neutrino.Comment: 1 typo in Eq.2 correcte
The Character of Z-pole Data Constraints on Standard Model Parameters
Despite the impressive precision of the Z-pole measurements made at LEP and
SLC, the allowed region for the principle Standard Model parameters responsible
for radiative corrections (the mass of the Higgs, the mass of the top and
alpha(Mz)) is still large enough to encompass significant non-linearities. The
nature of the experimental constraints therefore depends in an interesting way
on the "accidental" relationships among the various measurements. In
particular, the fact that the Z-pole measurements favor values of the Higgs
mass excluded by direct searches leads us to examine the effects of external
Higgsstrahlung, a process ignored by the usual precision electroweak
calculations.Comment: 9 pages, 6 figures, REVTeX format; added reference in section IV;
added paragraph on widths and a few cosmetic changes to correspond to
published versio
Hadron multiplicities in e+e- annihilation with heavy primary quarks
The multiple hadron production in the events induced by the heavy primary
quarks in annihilation is reconsidered with account of corrected
experimental data. New value for the multiplicity in events is
presented on the basis of pQCD estimates.Comment: 16 pages, 6 figures. Version accepted for publication in EPJ
Colour reconnections in Herwig++
We describe the implementation details of the colour reconnection model in
the event generator Herwig++. We study the impact on final-state observables in
detail and confirm the model idea from colour preconfinement on the basis of
studies within the cluster hadronization model. Moreover, we show that the
description of minimum bias and underlying event data at the LHC is improved
with this model and present results of a tune to available data.Comment: 19 pages, 21 figures, 2 tables. Matches with published versio
Finite energy chiral sum rules in QCD
The saturation of QCD chiral sum rules of the Weinberg-type is analyzed using
ALEPH and OPAL experimental data on the difference between vector and
axial-vector correlators (V-A). The sum rules exhibit poor saturation up to
current energies below the tau-lepton mass. A remarkable improvement is
achieved by introducing integral kernels that vanish at the upper limit of
integration. The method is used to determine the value of the finite remainder
of the (V-A) correlator, and its first derivative, at zero momentum:
and
. The dimension and
vacuum condensates in the Operator Product Expansion are also determined:
and Comment: Additional references added. No changes in results/conslusion
Exploring Flavor Structure of Supersymmetry Breaking at B factories
We investigate quark flavor signals in three different supersymmetric models,
the minimal supergravity, the SU(5) SUSY GUT with right handed neutrinos, and
the minimal supersymmetric standard model with U(2) flavor symmetry, in order
to study physics potential of the present and future factories. We evaluate
CP asymmetries in various B decay modes, , ,
and . The allowed regions of the CP asymmetry in
and are different for the three models so that
precise determinations of these observables in near future experiments are
useful to distinguish the three models. We also investigate possible deviations
from the standard model predictions of CP asymmetries in other B decay modes.
In particular, a large deviation is possible for the U(2) model. The
consistency check of the unitarity triangle including , and so on, at future high
luminosity factories and hadronic experiments is therefore
important to distinguish flavor structures of different supersymmetric models.Comment: revtex4, 31 pages, 7 figure
Anomalous behavior of pion production in high energy particle collisions
A shape of invariant differential cross section for charged hadron production
as function of transverse momentum measured in various collider experiments is
analyzed. Contrary to the behavior of produced charged kaons, protons and
antiprotons, the pion spectra require an anomalously high contribution of an
exponential term to describe the shape.Comment: 4 pages, 6 figure
The QCD Coupling Constant
This paper presents a summary of the current status of determinations of the
strong coupling constant alpha_s. A detailed description of the definition,
scale dependence and inherent theoretical ambiguities is given. The various
physical processes that can be used to determine alpha_s are reviewed and
attention is given to the uncertainties, both theoretical and experimental.Comment: 56 page
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