7,234 research outputs found

### The $\tau$-W Coupling

We interpret the existing experimental knowledge on $\tau$ decays in terms of the vector and axial vector couplings to the W boson, $V_{\tau}$ and $A_{\tau}$. We deduce $V_{\tau} = 1.00 \pm 0.09$ and $A_{\tau} = 1.00 \pm 0.09$ in agreement with the Standard Model predictions of $1$

### Virtual Supersymmetric Corrections in e^+e^- Annihilation

Depending on their masses, Supersymmetric particles can affect various
measurements in Z decay. Among these are the total width (or consequent
extracted value of $\alpha_s$), enhancement or suppression of various flavors,
and left-right and forward-backward asymmetries. The latter depend on squark
mass splittings and are, therefore, a possible test of the Supergravity related
predictions. We calculate leading order corrections for these quantities
considering in particular the case of light photino and gluino where the SUSY
effects are enhanced. In this limit the effect on $\alpha_s$ is appreciable,
the effect on $R_b$ is small, and the effect on the asymmetries is extremely
small.Comment: 11 pages, LaTeX, 3 figures, revised, a reference adde

### Flux of Atmospheric Neutrinos

Atmospheric neutrinos produced by cosmic-ray interactions in the atmosphere
are of interest for several reasons. As a beam for studies of neutrino
oscillations they cover a range of parameter space hitherto unexplored by
accelerator neutrino beams. The atmospheric neutrinos also constitute an
important background and calibration beam for neutrino astronomy and for the
search for proton decay and other rare processes. Here we review the literature
on calculations of atmospheric neutrinos over the full range of energy, but
with particular attention to the aspects important for neutrino oscillations.
Our goal is to assess how well the properties of atmospheric neutrinos are
known at present.Comment: 68 pages, 26 figures. With permission from the Annual Review of
Nuclear & Particle Science. Final version of this material is scheduled to
appear in the Annual Review of Nuclear & Particle Science Vol. 52, to be
published in December 2002 by Annual Reviews (http://annualreviews.org

### A compact and light-weight refractive telescope for the observation of extensive air showers

A general purpose instrument for imaging of Cherenkov light or fluorescence
light emitted by extensive air showers is presented. Its refractive optics
allows for a compact and light-weight design with a wide field-of-view of
12{\deg}. The optical system features a 0.5 m diameter Fresnel lens and a
camera with 61 pixels composed of Winston cones and large-sized 6x6 mm photo
sensors. As photo sensors, semi conductor light sensors (SiPMs) are utilized.
The camera provides a high photon detection efficiency together with robust
operation. The enclosed optics permit operation in regions of harsh
environmental conditions. The low price of the telescope allows the production
of a large number of telescopes and the application of the instrument in
various projects, such as FAMOUS for the Pierre Auger Observatory, HAWC's Eye
for HAWC or IceAct for IceCube. In this paper the novel design of this
telescope and first measurements are presented.Comment: Submitted to JINST, second (minor) revisio

### Mass Dependent $\alpha_S$ Evolution and the Light Gluino Existence

There is an intriguing discrepancy between \alpha_s(M_Z) values measured
directly at the CERN $Z_0$-factory and low-energy (at few GeV) measurements
transformed to $Q=M_{Z_0}$ by a massless QCD \alpha_s(Q) evolution relation.
There exists an attempt to reconcile this discrepancy by introducing a light
gluino \gl in the MSSM.
We study in detail the influence of heavy thresholds on \alpha_s(Q)
evolution. First, we consruct the "exact" explicit solution to the
mass-dependent two-loop RG equation for the running \alpha_s(Q). This solution
describes heavy thresholds smoothly. Second, we use this solution to
recalculate anew \alpha_s(M_Z) values corresponding to "low-energy" input data.
Our analysis demonstrates that using {\it mass-dependent RG procedure}
generally produces corrections of two types: Asymptotic correction due to
effective shift of threshold position; Local threshold correction only for the
case when input experiment lies in the close vicinity of heavy particle
threshold: $Q_{expt} \simeq M_h$.
Both effects result in the effective shift of the \asmz values of the order
of $10^{-3}$. However, the second one could be enhanced when the gluino mass is
close to a heavy quark mass. For such a case the sum effect could be important
for the discussion of the light gluino existence as it further changes the
\gl mass.Comment: 13, Late

### Implications of LEP Results for SO(10) Grandunification with Two Intermediate Stages

We consider the breaking of the grand unification group $SO(10)$ to the
standard model gauge group through several chains containing two intermediate
stages. Using the values of the gauge coupling constants at scale $M_Z$ derived
from recent LEP data, we determine the range of their intermediate and
unification scales. In particular, we identify those chains that permit new
gauge structure at relatively low energy $(\sim 1\, {\rm TeV})$.Comment: (LATEX, 9 pages + 3 pages of figures not included) OITS-48

### Standard Model Physics at LEP

Selected topics on precision tests of the Standard Model of the Electroweak
and the Strong Interaction at the LEP $e^+e^-$ collider are presented,
including an update of the world summary of measurements of $\alpha_s$,
representing the state of knowledge of summer 1999. This write-up of lecture
notes consists of a reproduction of slides, pictures and tables, supplemented
by a short descriptive text and a list of relevant references.Comment: lecture given at Intern. Summer School at Nijmegen, August 1999, 44
pages, 36 (mostly coloured) figures, LaTeX, needs crckapb.st

### Simulation of Atmospheric Muon and Neutrino Fluxes with CORSIKA

The fluxes of atmospheric muons and neutrinos are calculated by a three
dimensional Monte Carlo simulation with the air shower code CORSIKA using the
hadronic interaction models DPMJET, VENUS, GHEISHA, and UrQMD. For the
simulation of low energy primary particles the original CORSIKA has been
extended by a parametrization of the solar modulation and a microscopic
calculation of the directional dependence of the geomagnetic cut-off functions.
An accurate description for the geography of the Earth has been included by a
digital elevation model, tables for the local magnetic field in the atmosphere,
and various atmospheric models for different geographic latitudes and annual
seasons. CORSIKA is used to calculate atmospheric muon fluxes for different
locations and the neutrino fluxes for Kamioka. The results of CORSIKA for the
muon fluxes are verified by an extensive comparison with recent measurements.
The obtained neutrino fluxes are compared with other calculations and the
influence of the hadronic interaction model, the geomagnetic cut-off and the
local magnetic field on the neutrino fluxes is investigated.Comment: revtex, 19 pages, 19 Postscript figures, submitted to Phys. Rev.

### Deep-Inelastic Final States in a Space-Time Description of Shower Development and Hadronization

We extend a quantum kinetic approach to the description of hadronic showers
in space, time and momentum space to deep-inelastic $ep$ collisions, with
particular reference to experiments at HERA. We follow the history of hard
scattering events back to the initial hadronic state and forward to the
formation of colour-singlet pre-hadronic clusters and their decays into
hadrons. The time evolution of the space-like initial-state shower and the
time-like secondary partons are treated similarly, and cluster formation is
treated using a spatial criterion motivated by confinement and a
non-perturbative model for hadronization. We calculate the time evolution of
particle distributions in rapidity, transverse and longitudinal space. We also
compare the transverse hadronic energy flow and the distribution of observed
hadronic masses with experimental data from HERA, and find encouraging results.
The techniques developed in this paper may be applied in the future to more
complicated processes such as eA, pp, pA and AA collisions.Comment: 44 pages plus 14 postscript figure

### Space, Time and Color in Hadron Production Via e+e- -> Z0 and e+e- -> W+W-

The time-evolution of jets in hadronic e+e- events at LEP is investigated in
both position- and momentum-space, with emphasis on effects due to color flow
and particle correlations. We address dynamical aspects of the four
simultanously-evolving, cross-talking parton cascades that appear in the
reaction e+e- -> gamma/Z0 -> W+W- -> q1 q~2 q3 q~4, and compare with the
familiar two-parton cascades in e+e- -> Z0 -> q1 q~2. We use a QCD statistical
transport approach, in which the multiparticle final state is treated as an
evolving mixture of partons and hadrons, whose proportions are controlled by
their local space-time geography via standard perturbative QCD parton shower
evolution and a phenomenological model for non-perturbative parton-cluster
formation followed by cluster decays into hadrons. Our numerical simulations
exhibit a characteristic `inside-outside' evolution simultanously in position
and momentum space. We compare three different model treatments of color flow,
and find large effects due to cluster formation by the combination of partons
from different W parents. In particular, we find in our preferred model a shift
of several hundred MeV in the apparent mass of the W, which is considerably
larger than in previous model calculations. This suggests that the
determination of the W mass at LEP2 may turn out to be a sensitive probe of
spatial correlations and hadronization dynamics.Comment: 52 pages, latex, 18 figures as uu-encoded postscript fil

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