551 research outputs found
Bosonic Quartic Couplings at LEP2
We list the set of C and P conserving anomalous quartic vector bosons
self-couplings which can be tested at LEP2 through triple vector boson
production. We show how this set can be embedded in manifestly SU(2)xU(1) gauge
invariant operators exhibiting an SU(2)_c global symmetry. We derive bounds on
these various couplings and show the most relevant distributions that can
enhance their contribution. We also find that an e+e- collider running at 500
GeV can improve the LEP2 limits by as much as three orders of magnitude.Comment: 21 pages, 7 figure
Cryogenic detectors for particle physics
Ăcole thĂ©matiqu
from LEP to linear collider energies
The complete tree level cross section for the process is computed using the GRACE system, a program package for
automatic amplitude calculation. Special attention is brought to the gauge
violation problem induced by the finite width of the -boson. The {\it
preserved gauge scheme} is introduced and an event generator which includes
double-resonant, single-resonant and non-resonant diagrams with no need for a
cut on the electron polar angle is presented. Since no cut needs to be applied
to the electron, the generator can be used to estimate background for searches
involving jets and missing energy. A monojet event rate estimation based on
this process at LEP-I energy is discussed.Comment: 18 pages, uses epsfig.sty, 10 postscript figures. revised for minor
change of the text at Dec 6 199
QCD
We discuss issues of QCD at the LHC including parton distributions, Monte
Carlo event generators, the available next-to-leading order calculations,
resummation, photon production, small x physics, double parton scattering, and
backgrounds to Higgs production.Comment: 115 pages, Latex, 47 figures, to appear in the Report of the ``1999
CERN Workshop on SM Physics (and more) at the LHC'', S. Catani, M. Dittmar,
D. Soper, W.J. Stirling, S. Tapprogge (convenors
susy23 v2.0: an Event Generator for Supersymmetric Processes at Colliders
\susy23 is a Monte-Carlo package for generating supersymmetric (SUSY)
processes at colliders. Twenty-three types of SUSY processes with 2 or
3 final state particles at tree level are included in version 2.0. {\susy23}
addresses event simulation requirements at colliders such as LEP.
Matrix elements are generated by GRACE with the helicity amplitude method for
processes involving massive fermions. The phase space integration of the matrix
element gives the total and differential cross sections, then unweighted events
are generated. Sparticle widths and decay branching ratios are calculated. Each
final state particle may then decay according to these probabilities. Spin
correlations are taken into account in the decays of sparticles. Corrections of
initial state radiation (ISR) are implemented in two ways, one is based on the
electron structure function formalism and the second uses the parton shower
algorithm called QEDPS. Parton shower and hadronization of the final quarks are
performed through an interface to JETSET.Comment: 36 pages, LaTe
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
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
Direct Observation of Longitudinally Polarised W Bosons
The three different helicity states of W bosons, produced in the reaction
e+e- -> W+W- -> l nu q q~ are studied using leptonic and hadronic W decays at
sqrt{s}=183GeV and 189GeV. The W polarisation is also measured as a function of
the scattering angle between the W- and the direction of the e- beam. The
analysis demonstrates that W bosons are produced with all three helicities, the
longitudinal and the two transverse states. Combining the results from the two
center-of-mass energies and with leptonic and hadronic W decays, the fraction
of longitudinally polarised W bosons is measured to be 0.261 +/- 0.051(stat.)
+/- 0.016(syst.) in agreement with the expectation from the Standard Model
Search for Neutral Higgs Bosons of the Minimal Supersymmetric Standard Model in e+e- Interactions at \sqrt{s} = 189 GeV
A search for the lightest neutral scalar and neutral pseudoscalar Higgs
bosons in the Minimal Supersymmetric Standard Model is performed using 176.4
pb^-1 of integrated luminosity collected by L3 at a center-of-mass energy of
189 GeV. No signal is observed, and the data are consistent with the expected
Standard Model background. Lower limits on the masses of the lightest neutral
scalar and pseudoscalar Higgs bosons are given as a function of tan(beta).
Lower mass limits for tan(beta)>1 are set at the 95% confidence level to be m_h
> 77.1 GeV and m_A > 77.1 GeV
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