622 research outputs found
A wide scalar neutrino resonance and b\bar{b} production at LEP
In supersymmetric models with R-parity violation, scalar neutrinos may be
produced as s-channel resonances in e^+e^- colliders. We note that within
current constraints, the scalar neutrino may have a width of several GeV into
b\bar{b} and be produced with large cross section, leading to a novel
supersymmetry discovery signal at LEP II. In addition, if the scalar neutrino
mass approximately equals m_Z, such a resonance necessarily increases R_b and
reduces A_{FB}(b), significantly improving the fit to electroweak data. Bounds
from B meson and top quark decays are leading constraints, and we stress the
importance of future measurements.Comment: 8 pages. LaTex + RevTex. Revised to include a discussion of ISR
effects. Version to appear in Phys. Rev. Let
GEANT4 : a simulation toolkit
Abstract Geant4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics. PACS: 07.05.Tp; 13; 2
Search for Branons at LEP
We search, in the context of extra-dimension scenarios, for the possible
existence of brane fluctuations, called branons. Events with a single photon or
a single Z-boson and missing energy and momentum collected with the L3 detector
in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are
analysed. No excess over the Standard Model expectations is found and a lower
limit at 95% confidence level of 103 GeV is derived for the mass of branons,
for a scenario with small brane tensions. Alternatively, under the assumption
of a light branon, brane tensions below 180 GeV are excluded
Study of Spin and Decay-Plane Correlations of W Bosons in the e+e- -> W+W- Process at LEP
Data collected at LEP at centre-of-mass energies \sqrt(s) = 189 - 209 GeV are
used to study correlations of the spin of W bosons using e+e- -> W+W- -> lnqq~
events. Spin correlations are favoured by data, and found to agree with the
Standard Model predictions. In addition, correlations between the W-boson decay
planes are studied in e+e- -> W+W- -> lnqq~ and e+e- -> W+W- -> qq~qq~ events.
Decay-plane correlations, consistent with zero and with the Standard Model
predictions, are measured
Study of Z Boson Pair Production in e+e- Collisions at LEP at \sqrt{s}=189 GeV
The pair production of Z bosons is studied using the data collected by the L3
detector at LEP in 1998 in e+e- collisions at a centre-of-mass energy of 189
GeV. All the visible final states are considered and the cross section of this
process is measured to be 0.74 +0.15 -0.14 (stat.) +/- 0.04 (syst.) pb. Final
states containing b quarks are enhanced by a dedicated selection and their
production cross section is found to be 0.18 +0.09 -0.07 (stat.) +/- 0.02
(syst.) pb. Both results are in agreement with the Standard Model predictions.
Limits on anomalous couplings between neutral gauge bosons are derived from
these measurements
Formation of the in Two-Photon Collisions at LEP
The two-photon width of the meson has been
measured with the L3 detector at LEP. The is studied in the decay
modes , KK, KK,
KK, , , and
using an integrated luminosity of 140 pb at GeV and
of 52 pb at GeV. The result is
(BR) keV. The dependence of the cross section is studied for
GeV. It is found to be better described by a Vector Meson
Dominance model form factor with a J-pole than with a -pole. In addition,
a signal of events is observed at the mass. Upper limits
for the two-photon widths of the , , and are also
given
Ultrarelativistic sources in nonlinear electrodynamics
The fields of rapidly moving sources are studied within nonlinear
electrodynamics by boosting the fields of sources at rest. As a consequence of
the ultrarelativistic limit the delta-like electromagnetic shock waves are
found. The character of the field within the shock depends on the theory of
nonlinear electrodynamics considered. In particular, we obtain the field of an
ultrarelativistic charge in the Born-Infeld theory.Comment: 10 pages, 3 figure
Search for Scalar Leptons in e+e- collisions at \sqrt{s}=189 GeV
We report the result of a search for scalar leptons in e+e- collisions at 189
GeV centre-of-mass energy at LEP. No evidence for such particles is found in a
data sample of 176 pb^{-1}. Improved upper limits are set on the production
cross sections for these new particles. New exclusion contours in the parameter
space of the Minimal Supersymmetric Standard Model are derived, as well as new
lower limits on the masses of these supersymmetric particles. Under the
assumptions of common gaugino and scalar masses at the GUT scale, we set an
absolute lower limit on the mass of the lightest scalar electron of 65.5 Ge
Measurement of the Cross Section for Open-Beauty Production in Photon-Photon Collisions at LEP
The cross section for open-beauty production in photon-photon collisions is
measured using the whole high-energy and high-luminosity data sample collected
by the L3 detector at LEP. This corresponds to 627/pb of integrated luminosity
for electron-positron centre-of-mass energies from 189GeV to 209GeV. Events
containing b quarks are identified through their semi-leptonic decay into
electrons or muons. The e+e- -> e+e-b b~X cross section is measured within our
fiducial volume and then extrapolated to the full phase space. These results
are found to be in significant excess with respect to Monte Carlo predictions
and next-to-leading order QCD calculations
Measurement of Exclusive rho^0 rho^0 Production in Two-Photon Collisions at High Q^2 at LEP
Exclusive rho rho production in two-photon collisions involving a single
highly virtual photon is studied with data collected at LEP at centre-of-mass
energies 89GeV < \sqrt{s} < 209GeV with a total integrated luminosity of
854.7pb^-1 The cross section of the process gamma gamma^* -> rho rho is
determined as a function of the photon virtuality, Q^2 and the two-photon
centre-of-mass energy, Wgg, in the kinematic region: 1.2GeV^2 < Q^2 < 30GeV^2
and 1.1GeV < Wgg < 3GeV
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