3,847 research outputs found
Pair production of the T-odd leptons at the LHC
The T-odd leptons predicted by the littlest model with T-parity can
be pair produced via the subprocesses ,
, and (= or
) at the Large Hadron Collider . We estimate the hadronic
production cross sections for all of these processes and give a simply
phenomenology analysis. We find that the cross sections for most of the above
processes are very small. However, the value of the cross section for the
process can reach .Comment: 12 pages, 2 figure
Photon-induced production of the mirror quarks from the model at the
The photon-induced processes at the provide clean experimental
conditions due to absence of the proton remnants, which might produce
complementary and interesting results for tests of the standard model and for
searching of new physics. In the context of the littlest model with
T-parity, we consider the photon-induced production of the mirror quarks at the
. The cross sections for various production channels are calculated and a
simply phenomenology analysis is performed by assuming leptonic decays.Comment: 20 pages, 10 figure
Testbeam and Laboratory Characterization of CMS 3D Pixel Sensors
The pixel detector is the innermost tracking device in CMS, reconstructing
interaction vertices and charged particle trajectories. The sensors located in
the innermost layers of the pixel detector must be upgraded for the ten-fold
increase in luminosity expected with the High- Luminosity LHC (HL-LHC) phase.
As a possible replacement for planar sensors, 3D silicon technology is under
consideration due to its good performance after high radiation fluence. In this
paper, we report on pre- and post- irradiation measurements for CMS 3D pixel
sensors with different electrode configurations. The effects of irradiation on
electrical properties, charge collection efficiency, and position resolution of
3D sensors are discussed. Measurements of various test structures for
monitoring the fabrication process and studying the bulk and surface
properties, such as MOS capacitors, planar and gate-controlled diodes are also
presented.Comment: 14 page
Constraints on new interactions from neutron scattering experiments
Constraints for the constants of hypothetical Yukawa-type corrections to the
Newtonian gravitational potential are obtained from analysis of neutron
scattering experiments. Restrictions are obtained for the interaction range
between 10^{-12} and 10^{-7} cm, where Casimir force experiments and atomic
force microscopy are not sensitive. Experimental limits are obtained also for
non-electromagnetic inverse power law neutron-nucleus potential. Some
possibilities are discussed to strengthen these constraints.Comment: 18 pages, 3 figure
UV friendly T-parity in the SU(6)/Sp(6) little Higgs model
Electroweak precision tests put stringent constraints on the parameter space
of little Higgs models. Tree-level exchange of TeV scale particles in a generic
little Higgs model produce higher dimensional operators that make contributions
to electroweak observables that are typically too large. To avoid this problem
a discrete symmetry dubbed T-parity can be introduced to forbid the dangerous
couplings. However, it was realized that in simple group models such as the
littlest Higgs model, the implementation of T-parity in a UV completion could
present some challenges. The situation is analogous to the one in QCD where the
pion can easily be defined as being odd under a new symmetry in the
chiral Lagrangian, but this is not a symmetry of the quark Lagrangian. In
this paper we examine the possibility of implementing a T-parity in the low
energy model that might be easier to realize in the UV. In our
model, the T-parity acts on the low energy non-linear sigma model field in way
which is different to what was originally proposed for the Littlest Higgs, and
lead to a different low energy theory. In particular, the Higgs sector of this
model is a inert two Higgs doublets model with an approximate custodial
symmetry. We examine the contributions of the various sectors of the model to
electroweak precision data, and to the dark matter abundance.Comment: 21 pages,4 figures. Clarifications added, typos corrected and
references added. Published in JHE
T-parity, its problems and their solution
We point out a basic difficulty in the construction of little-Higgs models
with T-parity which is overlooked by large part of the present literature.
Almost all models proposed so far fail to achieve their goal: they either
suffer from sizable electroweak corrections or from a breakdown of collective
breaking. We provide a model building recipe to bypass the above problem and
apply it to build the simplest T-invariant extension of the Littlest Higgs. Our
model predicts additional T-odd pseudo-Goldstone bosons with weak scale masses.Comment: 25 pages, 2 appendice
Dangerous Skyrmions in Little Higgs Models
Skyrmions are present in many models of electroweak symmetry breaking where
the Higgs is a pseudo-Goldstone boson of some strongly interacting sector. They
are stable, composite objects whose mass lies in the range 10-100 TeV and can
be naturally abundant in the universe due to their small annihilation
cross-section. They represent therefore good dark matter candidates. We show
however in this work that the lightest skyrmion states are electrically charged
in most of the popular little Higgs models, and hence should have been directly
or indirectly observed in nature already. The charge of the skyrmion under the
electroweak gauge group is computed in a model-independent way and is related
to the presence of anomalies in the underlying theory via the
Wess-Zumino-Witten term.Comment: 31 pages, 4 figures; v2: minor changes, one reference added, version
to appear in JHEP; v3: erratum added, conclusions unchange
On measurement of top polarization as a probe of production mechanisms at the LHC
In this note we demonstrate the use of top polarization in the study of resonances at the LHC, in the possible case where the dynamics implies
a non-zero top polarization. As a probe of top polarization we construct an
asymmetry in the decay-lepton azimuthal angle distribution (corresponding to
the sign of ) in the laboratory. The asymmetry is non-vanishing
even for a symmetric collider like the LHC, where a positive axis is not
uniquely defined. The angular distribution of the leptons has the advantage of
being a faithful top-spin analyzer, unaffected by possible anomalous
couplings, to linear order. We study, for purposes of demonstration, the case
of a as might exist in the little Higgs models. We identify kinematic cuts
which ensure that our asymmetry reflects the polarization in sign and
magnitude. We investigate possibilities at the LHC with two energy options:
TeV and TeV, as well as at the Tevatron. At the
LHC the model predicts net top quark polarization of the order of a few per
cent for GeV, being as high as for a smaller mass
of the of GeV and for the largest allowed coupling in the model, the
values being higher for the TeV option. These polarizations translate to a
deviation from the standard-model value of azimuthal asymmetry of up to about
() for () TeV LHC, whereas for the Tevatron, values as high as
are attained. For the TeV LHC with an integrated luminosity of 10
fb, these numbers translate into a sensitivity over a large
part of the range GeV.Comment: 28 page, LaTeX, requires JHEP style file, 12 figures. Typos corrected
and references adde
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