3,281 research outputs found
Lepton flavor conserving Z -> l^+ l^-$ decays in the general two Higgs doublet model
We calculate the new physics effects to the branching ratios of the lepton
flavor conserving decays Z -> l^+ l^- in the framework of the general two Higgs
Doublet model. We predict the upper limits for the couplings
|\bar{\xi}^{D}_{N,\mu\tau}| and |\bar{\xi}^{D}_{N,\tau\tau}| as 3\times 10^2
GeV and 1\times 10^2 GeV, respectively.Comment: 9 pages, 3 figure
Production, Decay, and Polarization of Excited Heavy Hadrons
We discuss the production via fragmentation of excited heavy mesons and
baryons, and their subsequent decay. In particular, we consider the question of
whether a net polarization of the initial heavy quark may be detected, either
in a polarization of the final ground state or in anisotropies in the decay
products of the excited hadron. The result hinges in part on a nonperturbative
parameter which measures the net transverse alignment of the light degrees of
freedom in the fragmentation process. We use existing data on charmed mesons to
extract this quantity for certain excited mesons. Using this result, we
estimate the polarization retention of charm and bottom baryons.Comment: 37 pages, 3 figures available upon request, uses phyzzx forma
Collider discovery limits for supersymmetric Higgs bosons
The prospects for discovery of the five Higgs bosons of the minimal
supersymmetric standard model are assessed for existing and planned future
colliders, including LEP\,I, LEP\,II, LHC and SSC. As a benchmark for
comparisons, we take a top-quark mass GeV and squark mass parameter
TeV in evaluating one-loop radiative corrections; some results
for other values are also given. Searches based on the most promising
production and decay channels are taken into account. For large regions in
parameter space, detectable signals are predicted for one or more of the Higgs
bosons, but there remains a region for which no signals would be visible at the
above colliders.Comment: 24 pages, 23 postscript figures available on request. MAD/PH/69
Bounds on Vector Leptoquarks
We derive bounds on vector leptoquarks coupling to the first generation,
using data from low energy experiments as well as from high energy
accelerators. Similarly to the case of scalar leptoquarks, we find that the
strongest indirect bounds arise from atomic parity violation and universality
in leptonic pi decays. These bounds are considerably stronger than the first
direct bounds of HERA, restricting vector leptoquarks that couple with
electromagnetic strength to right-handed quarks to lie above 430 GeV or 460
GeV, and leptoquarks that couple with electromagnetic strength to left-handed
quarks to lie above 1.3 TeV, 1.2 TeV and 1.5 TeV for the SU(2)_W singlet,
doublet and triplet respectively.Comment: 14 Pages (LaTeX), including 1 uufiled postscript figure.
WIS-93/119/Dec-P
Optimized Variables of the Study of Polarization
The value of the -baryon polarization can be extracted from inclusive data
at LEP with better than 10\% precision based on current statistics. We present
a new variable by which to measure the polarization, which is the ratio of the
average electron energy to the average neutrino energy. This variable is both
sensitive to polarization and insensitive to fragmentation uncertainties.Comment: 10 pages (LaTeX), 2 figures, MIT-CTP-2270, CERN-PPE/94-0
Leptoquark production in ultrahigh-energy neutrino interactions revisited
The prospects for producing leptoquarks (LQs) in ultrahigh-energy (UHE)
neutrino nucleon collisions are re-examined in the light of recent
interpretations of HERA data in terms of leptoquark production. We update
predictions for cross-sections for the production of first- and
second-generation leptoquarks in UHE nu-N and nubar-N collisions including
(i) recent experimental limits on masses and couplings from the LEP and
TEVATRON colliders as well as rare processes,
(ii) modern parton distributions, and
(iii) radiative corrections to single leptoquark production.
If the HERA events are due to an SU(2) doublet leptoquark which couples
mainly to (e+,q) states, we argue that there are likely other LQ states which
couple to neutrinos which are close in mass, due to constraints from precision
electroweak measurements.Comment: 12 pages, LaTeX, 3 separate postscript figures. Added 1 reference
plus discussion, updated another referenc
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
Tevatron Mass Limits for Heavy Quarks Decaying via Flavor Changing Neutral Current
The dimuon and dielectron data from the Tevatron collider are used
to probe for heavy quarks, which decay dominantly via flavour changing neutral
current. Depending on whether the decay occurs at the tree or loop
level, one gets a lower mass limit of 85 or 75 GeV. The former applies to
singlet, vector doublet and mirror type quarks while the latter applies to a
lefthanded quark doublet of the fourth generation.Comment: 13 pages, TIFR/TH/92-58, Two figures to be supplied on reques
A Comprehensive Study of Leptoquark Bounds
We make a comprehensive study of indirect bounds on scalar leptoquarks that
couple chirally and diagonally to the first generation by examining available
data from low energy experiments as well as from high energy e+ e- and p pbar
accelerators. The strongest bounds turn out to arise from low energy data: For
leptoquarks that couple to right--handed quarks, the most stringent bound comes
from atomic parity violation. For leptoquarks that couple to left--handed
quarks, there are two mass regions: At low masses the bounds arise from atomic
parity violation or from universality in leptonic pi decays. At masses above a
few hundred GeV's, the dominant bounds come from the FCNC processes that are
unavoidable in these leptoquarks: The FCNC bound of the up sector, that arises
from D-Dbar mixing, combines with the FCNC bounds from the down sector, that
arise from rare K decays and K-Kbar mixing, to a bound on the flavour
CONSERVING coupling to the first generation.
The bounds restrict leptoquarks that couple with electromagnetic strength to
lie above 600 GeV or 630 GeV for leptoquarks that couple to RH quarks, and
above 1040 GeV, 440 GeV, and 750 GeV for the SU(2)_W scalar, doublet and
triplet leptoquarks that couple to LH quarks. These bounds are considerably
stronger than the first results from the direct searches at HERA. Our bounds
also already exclude large regions in the parameter space that could be
examined by various methods proposed for indirect leptoquark searches.Comment: 23 Pages (LaTeX), including 3 uufiled postscript figures.
WIS--93/90/Sept--PH. To appear in PRD. Changes: updated numbers ---> stronger
bound
Bounds on the mass of the b' quark, revisited
Recent results from the DELPHI collaboration led us to review the present
bounds on the b' quark mass. We use all available experimental data for m_b' >
96 GeV to constrain the b' quark mass as a function of the
Cabibbo-Kobayashi-Maskawa elements in a sequential four generations model. We
find that there is still room for a b' with a mass larger than 96 GeV.Comment: 9 pages and 7 figures. REVTEX
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