1,992 research outputs found
Measurements of the Production, Decay and Properties of the Top Quark: A Review
With the full Tevatron Run II and early LHC data samples, the opportunity for
furthering our understanding of the properties of the top quark has never been
more promising. Although the current knowledge of the top quark comes largely
from Tevatron measurements, the experiments at the LHC are poised to probe
top-quark production and decay in unprecedented regimes. Although no current
top quark measurements conclusively contradict predictions from the standard
model, the precision of most measurements remains statistically limited.
Additionally, some measurements, most notably the forward-backward asymmetry in
top quark pair production, show tantalizing hints of beyond-the-Standard-Model
dynamics. The top quark sample is growing rapidly at the LHC, with initial
results now public. This review examines the current status of top quark
measurements in the particular light of searching for evidence of new physics,
either through direct searches for beyond the standard model phenomena or
indirectly via precise measurements of standard model top quark properties
Searches for Physics Beyond the Standard Model at Colliders
All experimental measurements of particle physics today are beautifully
described by the Standard Model. However, there are good reasons to believe
that new physics may be just around the corner at the TeV energy scale. This
energy range is currently probed by the Tevatron and HERA accelerators and
selected results of searches for physics beyond the Standard Model are
presented here. No signals for new physics have been found and limits are
placed on the allowed parameter space for a variety of different particles.Comment: Proceedings for 2007 Europhysics Conference on High Energy Physics,
Manchester, July 200
Probing Top Anomalous Couplings at the Tevatron and the Large Hadron Collider
Chromomagnetic and chromoelectric dipole interactions of the top quark are
studied in a model independent framework. Limits are set on the scale of new
physics that might lead to such contributions using available Tevatron data.
Prospects at the LHC are reviewed.Comment: Version published in Praman
Phenomenology of the Heavy Flavored spin 3/2 Baryons in Light Cone QCD
Motivated by the results of the recent experimental discoveries for charm and
bottom baryons, the masses and magnetic moments of the heavy baryons with
containing a single heavy quark are studied within light cone QCD
sum rules method. Our results on the masses of heavy baryons are in good
agreement with predictions of other approaches, as well as with the existing
experimental data.Comment: 12 Pages, 18 Figures and 3 Tables. Based on: arXiv:0807.3481v2
[hep-ph](Nucl.Phys.B808:137-154,2009). To be Published in the Proceeding of
the International Conference on New Trends in High Energy Physics, 27 Sept.-4
Oct. 2008, Yalta, Crimea, Ukrain
Matching Tree-Level Matrix Elements with Interleaved Showers
We present an implementation of the so-called CKKW-L merging scheme for
combining multi-jet tree-level matrix elements with parton showers. The
implementation uses the transverse-momentum-ordered shower with interleaved
multiple interactions as implemented in PYTHIA8. We validate our procedure
using e+e--annihilation into jets and vector boson production in hadronic
collisions, with special attention to details in the algorithm which are
formally sub-leading in character, but may have visible effects in some
observables. We find substantial merging scale dependencies induced by the
enforced rapidity ordering in the default PYTHIA8 shower. If this rapidity
ordering is removed the merging scale dependence is almost negligible. We then
also find that the shower does a surprisingly good job of describing the
hardness of multi-jet events, as long as the hardest couple of jets are given
by the matrix elements. The effects of using interleaved multiple interactions
as compared to more simplistic ways of adding underlying-event effects in
vector boson production are shown to be negligible except in a few sensitive
observables. To illustrate the generality of our implementation, we also give
some example results from di-boson production and pure QCD jet production in
hadronic collisions.Comment: 44 pages, 23 figures, as published in JHEP, including all changes
recommended by the refere
Signals of CP Violation Beyond the MSSM in Higgs and Flavor Physics
We study an extension of the Higgs sector of the Minimal Supersymmetric
Standard Model (MSSM), considering the effects of new degrees of freedom at the
TeV scale, and allowing for sources of CP violation beyond the MSSM (BMSSM). We
analyze the impact of the BMSSM sources of CP violation on the Higgs collider
phenomenology and on low energy flavor and CP violating observables. We
identify distinct Higgs collider signatures that cannot be realized, either in
the case without CP violating phases or in the CP violating MSSM, and
investigate the prospects to probe them at the Tevatron and the LHC. The most
striking benchmark scenario has three neutral Higgs bosons that all decay
dominantly into W boson pairs and that are well within the reach of the 7 TeV
LHC run. On the other hand, we also present scenarios with three Higgs bosons
that have masses M_Hi > 150 GeV and decay dominantly into b bbar. Such
scenarios are much more challenging to probe and can even lie completely
outside the reach of the 7 TeV LHC run. We explore complementary scenarios with
standard MSSM Higgs signals that allow to accommodate a sizable B_s mixing
phase as indicated by D0, as well as the excess in B_s --> mu+ mu- candidates
recently reported by CDF. We find that, in contrast to the MSSM, a minimal
flavor violating soft sector is sufficient to generate significant corrections
to CP violating observables in meson mixing, compatible with EDM constraints.
In particular, a sizable B_s mixing phase, S_psiphi < 0.4, can be achieved for
specific regions of parameter space. Such a large B_s mixing phase would
unambiguously imply a sizable suppression of S_psiKs with respect to the SM
prediction and a BR(B_s --> mu+ mu-) close to the 95% C.L. upper bound reported
by CDF.Comment: 58 pages, 15 figures, 2 tables, v2 matches published versio
Model-independent extraction of matrix elements from top-quark measurements at hadron colliders
Current methods to extract the quark-mixing matrix element from
single-top production measurements assume that : top quarks decay into quarks with 100% branching fraction,
s-channel single-top production is always accompanied by a quark and
initial-state contributions from and quarks in the -channel
production of single top quarks are neglected. Triggered by a recent
measurement of the ratio
performed by the D0 collaboration, we consider a extraction method
that takes into account non zero d- and s-quark contributions both in
production and decay. We propose a strategy that allows to extract consistently
and in a model-independent way the quark mixing matrix elements ,
, and from the measurement of and from single-top
measured event yields. As an illustration, we apply our method to the Tevatron
data using a CDF analysis of the measured single-top event yield with two jets
in the final state one of which is identified as a -quark jet. We constrain
the matrix elements within a four-generation scenario by combining
the results with those obtained from direct measurements in flavor physics and
determine the preferred range for the top-quark decay width within different
scenarios.Comment: 36 pages, 17 figure
Precision measurements of the top quark mass from the Tevatron in the pre-LHC era
The top quark is the heaviest of the six quarks of the Standard Model.
Precise knowledge of its mass is important for imposing constraints on a number
of physics processes, including interactions of the as yet unobserved Higgs
boson. The Higgs boson is the only missing particle of the Standard Model,
central to the electroweak symmetry breaking mechanism and generation of
particle masses. In this Review, experimental measurements of the top quark
mass accomplished at the Tevatron, a proton-antiproton collider located at the
Fermi National Accelerator Laboratory, are described. Topologies of top quark
events and methods used to separate signal events from background sources are
discussed. Data analysis techniques used to extract information about the top
mass value are reviewed. The combination of several most precise measurements
performed with the two Tevatron particle detectors, CDF and \D0, yields a value
of \Mt = 173.2 \pm 0.9 GeV/.Comment: This version contains the most up-to-date top quark mass averag
Scalar-mediated forward-backward asymmetry
A large forward-backward asymmetry in production, for large
invariant mass of the system, has been recently observed by the CDF
collaboration. Among the scalar mediated mechanisms that can explain such a
large asymmetry, only the t-channel exchange of a color-singlet weak-doublet
scalar is consistent with both differential and integrated cross
section measurements. Constraints from flavor changing processes dictate a very
specific structure for the Yukawa couplings of such a new scalar. No sizable
deviation in the differential or integrated production cross section
is expected at the LHC.Comment: 22 pages, 1 figure and 2 tables. v2: Corrected Eqs.(50,51,74),
adapted Fig.1, Tab.1 and relevant discussions. Extended discussion of top
decay and single to
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