1,013 research outputs found
Top-quark physics at the first CLIC stage
The Compact Linear Collider (CLIC) is a mature option for a future
electron-positron collider operating at centre-of-mass energies of up to 3 TeV.
CLIC will be built and operated in a staged approach with three centre-of-mass
energies currently assumed to be 380 GeV, 1.5 TeV and 3 TeV. This contribution
discusses the prospects for precision measurements of top-quark properties at
the first stage of CLIC, based on detailed simulation studies, taking into
account luminosity spectra and beam induced backgrounds, full detector
simulation based on Geant4, final state reconstruction based on particle flow
approach with PandoraPFA, jet clustering with the VLC algorithm as implemented
in the FastJet package, and flavour tagging with LcfiPlus.
Based on a dedicated centre-of-mass energy scan around the top-quark pair
production threshold, the top-quark mass can be determined with a precision of
about 50 MeV in a theoretically well-defined manner. This scan is also
sensitive to the top-quark width and Yukawa coupling. Other approaches to
extract the top-quark mass at the first stage of CLIC make use of ISR photons
or the direct reconstruction of the top quarks. Precise measurements of the
differential top-quark pair production cross sections at 380 GeV, for different
electron beam polarisations, allow the study of top-quark couplings to
electroweak gauge bosons sensitive to new physics mass scales beyond 10 TeV.
The large number of top-quark pairs produced also allows competitive searches
for Flavour Changing Neutral Current (FCNC) top-quark decays with charm quarks
in the final state. Exclusion limits expected for 500 fb collected at
the first stage of CLIC are presented for , and channels, reaching down to for BR().Comment: 4 pages, 3 figures, to be submitted to proceedings of ICHEP'2018,
presented on behalf of the CLICdp Collaboratio
Leptoquark signal from global analysis
Data from HERA, LEP and the Tevatron, as well as from low energy experiments
are used to constrain the Yukawa couplings for scalar and vector leptoquarks in
the Buchmuller-Ruckl-Wyler effective model. In the limit of very high
leptoquark masses constraints on the coupling to the mass ratio l/M are derived
using the contact-interaction approximation. For finite masses the coupling
limits are studied as a function of the leptoquark mass. Some leptoquark models
are found to describe the existing experimental data much better than the
Standard Model. Increase in the global probability observed for models
including S_1 or ~V_o leptoquark production/exchange corresponds to more than a
3 sigma effect. Assuming that a real leptoquark signal is observed, calculated
is an allowed region in the l-M plane. The leptoquark signal is mostly
resulting from the new data on the atomic parity violation in cesium, but is
also supported by recent LEP2 measurements, unitarity violation in the CKM
matrix and HERA high-Q^2 results.Comment: Updated for DIS'2000, Liverpool, April 25-30,2000; 33 pages, 8
figures, 4 table
Measurement of the leptoquark Yukawa couplings in e+e- collisions at TESLA
Measurement of the Yukawa couplings of the first-generation leptoquarks has
been studied for e+e- collisions at TESLA, at sqrt(s)=800 GeV. By combining
measurements from different production and decay channels, determination of
Yukawa couplings with precision on the few per-cent level is possible. TESLA
will be sensitive to very small leptoquark Yukawa couplings not accessible at
LHC, down to lambda ~ 0.05 [e]. Distinction between left-handed and
right-handed Yukawa couplings is feasible even for leptoquark masses very close
to the pair-production kinematic limit.Comment: 20 pages, 15 figure
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Martian and terrestrial dust devils
When dust devils or convective vortices form they can be identified by specific meteorological parameters, a ‘signature’. If martian and terrestrial dust devil signatures are compared similarities can be identified
Study of the Higgs-boson decays into WW and ZZ at the Photon Collider
Production of the Standard Model Higgs-boson at the Photon Collider at TESLA
is studied for the Higgs-boson masses above 150 GeV. Simulation of signal and
background processes takes into account realistic luminosity spectra and
detector effects. In the considered mass range, large interference effects are
expected in the W+W- decay channel. By reconstructing W+W- and ZZ final states,
not only the h->gamma gamma partial width can be measured, but also the
relative phase of the scattering amplitude. This opens a new window for the
precise determination of the Higgs-boson couplings. Models with heavy,
fourth-generation fermions and with enlarged Higgs sector (2HDM (II)) are
considered.Comment: 19 pages, 18 figures; updated version with improved precision of
estimate
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Diurnal Dust Devil Behaviour for the Viking 1 Landing Site: Sols 1 to 30
Previous martian studies have provided an understanding of diurnal dust devil behaviour for Viking 2 and the Mars Pathfinder landing sites. It is the purpose of this work to complete this analysis by analysing the meteorological data from the Viking 1 landing site
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